crs-l2-fiji-antimeridian
Map (reference ← swipe → agent)
0:00
I'm pulling together per-transect coverage figures for our survey report, but some of the lines in fiji_transects_wgs84.geojson render as arcs spanning the entire globe instead of short local segments. Can you fix the geometries so they render correctly, convert them to Fiji's national metric grid, and give me each transect as one MultiLineString feature with a length_m attribute in metres?
Every feature must come out as a MultiLineString, so do not leave any transects as plain LineString, and the problematic ones must end up as multi-part geometries that faithfully represent the actual survey path. Carry the survey attributes (vessel and survey_date) through unchanged, use transect_id as the key field, and write the result as GeoJSON named fiji_transects_fmg.geojson.
0:00
System info
{
"adapter": "openrouter",
"model": "deepseek/deepseek-v4-flash",
"base_url": "https://openrouter.ai/api/v1"
}
0:03
Let me start by examining the input file to understand the data and identify the problematic geometries.
0:03
Read
/work/fiji_transects_wgs84.geojson
1 {
2 "type": "FeatureCollection",
3 "name": "fiji_transects_wgs84",
4 "crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:OGC:1.3:CRS84" } },
5 "features": [
6 { "type": "Feature", "properties": { "transect_id": "T001", "vessel": "Taveuni II", "survey_date": "2025-08-15", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 178.941879580782086, -17.632301816020771 ], [ 179.456655009654696, -17.623768593111961 ], [ 179.971430438527307, -17.611072392823225 ], [ -179.513794132600054, -17.596198176111951 ], [ -178.999018703727444, -17.579632069513806 ], [ -178.484243274854833, -17.577321872344196 ] ] } },
7 { "type": "Feature", "properties": { "transect_id": "T002", "vessel": "Bligh", "survey_date": "2025-08-12", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 179.070288824800542, -17.334767984150709 ], [ 179.725942881740252, -17.171343988196945 ], [ -179.618403061320009, -17.007726843860763 ], [ -178.962749004380299, -16.834850408534852 ] ] } },
8 { "type": "Feature", "properties": { "transect_id": "T003", "vessel": "Lomaiviti", "survey_date": "2025-08-12", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 177.636947428758333, -17.358837040696127 ], [ 178.462815605623859, -17.416074837434927 ], [ 179.288683782489386, -17.471713663377283 ], [ -179.885448040645059, -17.527675804260884 ], [ -179.059579863779533, -17.590577543375694 ] ] } },
9 { "type": "Feature", "properties": { "transect_id": "T004", "vessel": "Vanua I", "survey_date": "2025-08-15", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 178.873696381462679, -17.803295238757038 ], [ 179.542254331047587, -17.598477321703708 ], [ -179.789187719367533, -17.405549472537043 ], [ -179.120629769782624, -17.19411411231702 ], [ -178.452071820197745, -16.992332922174427 ], [ -177.783513870612836, -16.795171196845544 ] ] } },
10 { "type": "Feature", "properties": { "transect_id": "T005", "vessel": "Bligh", "survey_date": "2025-08-19", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 177.596924830927293, -17.923255155112717 ], [ 178.160696712947697, -18.010328270600898 ], [ 178.724468594968101, -18.099224972140938 ], [ 179.288240476988506, -18.17532145144995 ], [ 179.85201235900891, -18.270380145331412 ], [ -179.584215758970686, -18.358875431719703 ], [ -179.020443876950281, -18.437390943572723 ] ] } },
11 { "type": "Feature", "properties": { "transect_id": "T006", "vessel": "Cakaulevu", "survey_date": "2025-08-13", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 178.622166647099931, -18.382052393687179 ], [ 179.205668025282989, -18.184610858038685 ], [ 179.789169403466019, -17.991866703295319 ], [ -179.627329218350923, -17.789532271264445 ], [ -179.043827840167864, -17.595682751178369 ], [ -178.460326461984835, -17.393483000040479 ], [ -177.876825083801776, -17.203490564162109 ] ] } },
12 { "type": "Feature", "properties": { "transect_id": "T007", "vessel": "Vanua I", "survey_date": "2025-08-19", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 177.920101619592742, -17.14979850360189 ], [ 178.697177550619955, -17.100522188212071 ], [ 179.474253481647168, -17.053867486482115 ], [ -179.74867058732562, -17.004197778897627 ], [ -178.971594656298407, -16.959481244370728 ], [ -178.194518725271195, -16.911697858015476 ] ] } },
13 { "type": "Feature", "properties": { "transect_id": "T008", "vessel": "Taveuni II", "survey_date": "2025-08-12", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 179.401134548056262, -17.934415957637167 ], [ 179.67454249485786, -17.899654147497863 ], [ 179.947950441659486, -17.858130727687527 ], [ -179.778641611538916, -17.811143619533269 ], [ -179.50523366473729, -17.768768396969666 ], [ -179.231825717935692, -17.724708363613253 ] ] } },
14 { "type": "Feature", "properties": { "transect_id": "T009", "vessel": "Vanua I", "survey_date": "2025-08-13", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 178.068433112639013, -16.657838811131668 ], [ 178.561564721122721, -16.689731320158675 ], [ 179.054696329606429, -16.72173241552732 ], [ 179.547827938090137, -16.748891897767297 ], [ -179.959040453426155, -16.775241845025921 ], [ -179.465908844942447, -16.799281899607834 ] ] } },
15 { "type": "Feature", "properties": { "transect_id": "T010", "vessel": "Vanua I", "survey_date": "2025-08-15", "crosses_antimeridian_flag": true }, "geometry": { "type": "LineString", "coordinates": [ [ 177.602847396853463, -17.277026295424367 ], [ 179.128053569323441, -17.468285296635063 ], [ -179.346740258206609, -17.65419136085664 ], [ -177.82153408573663, -17.837325774502055 ] ] } },
16 { "type": "Feature", "properties": { "transect_id": "T011", "vessel": "Taveuni II", "survey_date": "2025-08-20", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -176.863797870333627, -17.7932433540029 ], [ -176.985724572324699, -17.81273654528005 ], [ -177.107651274315742, -17.824236921378098 ], [ -177.229577976306814, -17.835861250474697 ], [ -177.351504678297886, -17.857559546831705 ], [ -177.473431380288929, -17.871769203842408 ], [ -177.595358082280001, -17.890225470404214 ] ] } },
17 { "type": "Feature", "properties": { "transect_id": "T012", "vessel": "Taveuni II", "survey_date": "2025-08-20", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 176.312195951017685, -17.976122209608448 ], [ 176.362236324041447, -17.722210270969462 ], [ 176.412276697065209, -17.470306839752467 ], [ 176.462317070088972, -17.226475769084448 ] ] } },
18 { "type": "Feature", "properties": { "transect_id": "T013", "vessel": "Bligh", "survey_date": "2025-08-19", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -176.70823848972006, -17.696306145080879 ], [ -177.205026853648661, -17.960082567744127 ], [ -177.701815217577291, -18.210737758337459 ], [ -178.198603581505893, -18.469124252379427 ] ] } },
19 { "type": "Feature", "properties": { "transect_id": "T014", "vessel": "Lomaiviti", "survey_date": "2025-08-13", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 176.538496893308832, -16.594358164012139 ], [ 176.861572490827996, -16.71494251806207 ], [ 177.184648088347188, -16.832251271240672 ], [ 177.507723685866381, -16.976116506165042 ], [ 177.830799283385545, -17.090939089364483 ] ] } },
20 { "type": "Feature", "properties": { "transect_id": "T015", "vessel": "Vanua I", "survey_date": "2025-08-15", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -177.278377449219306, -16.724372731501912 ], [ -177.470251917030794, -16.761535677586746 ], [ -177.662126384842253, -16.787182414326686 ], [ -177.854000852653712, -16.818799270133983 ], [ -178.0458753204652, -16.856282470705128 ], [ -178.237749788276659, -16.891308864567598 ], [ -178.429624256088147, -16.914729063096839 ] ] } },
21 { "type": "Feature", "properties": { "transect_id": "T016", "vessel": "Taveuni II", "survey_date": "2025-08-15", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 178.445325115686984, -18.225562645051426 ], [ 178.570919872630384, -18.22187730118792 ], [ 178.696514629573755, -18.228085980840198 ], [ 178.822109386517127, -18.243164774607269 ], [ 178.947704143460527, -18.232257588046291 ] ] } },
22 { "type": "Feature", "properties": { "transect_id": "T017", "vessel": "Taveuni II", "survey_date": "2025-08-12", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -176.949497668404376, -16.593233226112279 ], [ -177.073130399044231, -16.796136633276152 ], [ -177.196763129684086, -16.985064764093782 ], [ -177.320395860323913, -17.188172387851619 ], [ -177.444028590963768, -17.380278567766066 ], [ -177.567661321603623, -17.571298263401527 ], [ -177.691294052243478, -17.76827441812642 ] ] } },
23 { "type": "Feature", "properties": { "transect_id": "T018", "vessel": "Bligh", "survey_date": "2025-08-19", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 176.111138114901024, -16.851117503263293 ], [ 176.291399614433374, -17.034309766495799 ], [ 176.471661113965695, -17.221302006070296 ], [ 176.651922613498016, -17.402317112686557 ], [ 176.832184113030365, -17.592994204367653 ] ] } },
24 { "type": "Feature", "properties": { "transect_id": "T019", "vessel": "Lomaiviti", "survey_date": "2025-08-12", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 178.007516628261584, -17.706954766350957 ], [ 177.596962177324428, -17.607161226082525 ], [ 177.186407726387301, -17.511279680346377 ], [ 176.775853275450146, -17.418568907300433 ], [ 176.36529882451299, -17.326891370330944 ] ] } },
25 { "type": "Feature", "properties": { "transect_id": "T020", "vessel": "Taveuni II", "survey_date": "2025-08-13", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 176.869640838143511, -17.085093978662378 ], [ 177.34023164697706, -17.269542693344249 ], [ 177.810822455810609, -17.442447410976666 ], [ 178.281413264644158, -17.624621823987695 ], [ 178.752004073477707, -17.807162082048386 ] ] } },
26 { "type": "Feature", "properties": { "transect_id": "T021", "vessel": "Vanua I", "survey_date": "2025-08-16", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 176.258661225850091, -17.092877710432774 ], [ 176.830345357965598, -17.521807453385343 ], [ 177.402029490081105, -17.943438299004075 ], [ 177.973713622196613, -18.366984215963161 ] ] } },
27 { "type": "Feature", "properties": { "transect_id": "T022", "vessel": "Vanua I", "survey_date": "2025-08-15", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 177.115699442929383, -17.820293640195572 ], [ 177.180354072206086, -17.755581112632651 ], [ 177.245008701482789, -17.684692899482695 ], [ 177.30966333075952, -17.61995755685173 ], [ 177.374317960036223, -17.544174647257226 ], [ 177.438972589312925, -17.479955835030527 ] ] } },
28 { "type": "Feature", "properties": { "transect_id": "T023", "vessel": "Lomaiviti", "survey_date": "2025-08-12", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -177.191351883954098, -17.679938619650844 ], [ -177.334313691261116, -17.740394590021616 ], [ -177.477275498568133, -17.794367957957562 ], [ -177.62023730587515, -17.835119945356809 ], [ -177.763199113182168, -17.904282380225705 ], [ -177.906160920489185, -17.955635131096855 ] ] } },
29 { "type": "Feature", "properties": { "transect_id": "T024", "vessel": "Vanua I", "survey_date": "2025-08-12", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -179.108274205314615, -16.84950325482971 ], [ -178.651703763804733, -16.962456436762313 ], [ -178.195133322294822, -17.077410225872036 ], [ -177.73856288078494, -17.187966865781235 ], [ -177.281992439275029, -17.288042922581088 ], [ -176.825421997765147, -17.40904519070677 ] ] } },
30 { "type": "Feature", "properties": { "transect_id": "T025", "vessel": "Taveuni II", "survey_date": "2025-08-19", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 176.574749815324452, -18.225329195672629 ], [ 176.575711406506713, -17.903825702399828 ], [ 176.576672997688945, -17.572376190438085 ], [ 176.577634588871206, -17.245872893430239 ] ] } },
31 { "type": "Feature", "properties": { "transect_id": "T026", "vessel": "Cakaulevu", "survey_date": "2025-08-19", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ 178.630248956242411, -17.547785158041279 ], [ 178.44215451378426, -17.570057172060459 ], [ 178.254060071326109, -17.598148620651486 ], [ 178.065965628867986, -17.611819625668215 ], [ 177.877871186409834, -17.645164465599024 ], [ 177.689776743951683, -17.659546383089758 ] ] } },
32 { "type": "Feature", "properties": { "transect_id": "T027", "vessel": "Vanua I", "survey_date": "2025-08-12", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -177.773526218774975, -17.183972526301677 ], [ -177.993798674497214, -17.290101550005915 ], [ -178.214071130219452, -17.383420029016879 ], [ -178.434343585941718, -17.487055860389813 ], [ -178.654616041663957, -17.584325384194859 ], [ -178.874888497386195, -17.694189986558115 ] ] } },
33 { "type": "Feature", "properties": { "transect_id": "T028", "vessel": "Vanua I", "survey_date": "2025-08-12", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -178.154921880223981, -16.519500569812283 ], [ -177.760867938660567, -16.61473611015824 ], [ -177.366813997097154, -16.706948361526067 ], [ -176.972760055533769, -16.779276042892469 ], [ -176.578706113970355, -16.874986722588798 ] ] } },
34 { "type": "Feature", "properties": { "transect_id": "T029", "vessel": "Lomaiviti", "survey_date": "2025-08-19", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -176.563841265411412, -18.091246216590591 ], [ -176.943316553982299, -17.796168551154441 ], [ -177.322791842553215, -17.510273970538908 ], [ -177.702267131124103, -17.231705179840109 ], [ -178.08174241969499, -16.949176694851047 ] ] } },
35 { "type": "Feature", "properties": { "transect_id": "T030", "vessel": "Cakaulevu", "survey_date": "2025-08-19", "crosses_antimeridian_flag": false }, "geometry": { "type": "LineString", "coordinates": [ [ -177.772700226865993, -16.898671712097919 ], [ -177.981739053528088, -17.042373280579991 ], [ -178.190777880190183, -17.175821795383495 ], [ -178.399816706852278, -17.32978967298839 ], [ -178.608855533514344, -17.474383681681747 ], [ -178.817894360176439, -17.613581860280195 ], [ -179.026933186838534, -17.755873350663471 ] ] } }
36 ]
37 }
0:30
Let me analyze the problem. The features with `crosses_antimeridian_flag: true` have coordinates that cross the antimeridian (180° longitude). For example, T001 has coordinates like: - 178.941..., 179.456..., 179.971..., -179.513..., -178.999..., -178.484... The issue is that when rendering software plots these, it sees a jump from 179.971 to -179.513, which goes the "long way" around the globe (across -180 to +180 is a gap of ~359 degrees, but the actual path should be a short segment across the date line). I need to: 1. For features crossing the antimeridian, split the linestring at the antimeridian, creating multi-part geometries 2. Add 360 to the negative longitude values on the "east" side of the antimeridian, or subtract 360 from positive values on the "west" side 3. Then project to Fiji's national metric grid system 4. Calculate length in metres 5. Output as MultiLineString GeoJSON Fiji's national metric grid... Let me think about this. Fiji uses a projection suitable for the Fiji region. The common one would be something like: - EPSG:3460 - Fiji 1956 / Fiji Map Grid - EPSG:3141 - maybe something else - Actually, Fiji Map Grid is EPSG:3460 (Fiji 1956 / Fiji Map Grid) or EPSG:3139 (Fiji 1956 / UTM zone 60S) - But there's also EPSG:2120 (Fiji 1986 / UTM zone 60S) - Actually, the most common "Fiji's national metric grid" is likely "Fiji Map Grid" which is EPSG:3460 (Fiji 1956 / Fiji Map Grid) or EPSG:3138 / 3139 (Fiji 1956 / UTM zones 59S and 60S) - Wait, let me check. Fiji Map Grid is EPSG:3460 (Fiji 1956 / Fiji Map Grid). That's a single grid covering all of Fiji. Actually, let me check what projections are available. But first, let me think about the approach. The key insight is: - For features that cross the antimeridian, the coordinates go from positive longitudes (east of 180°) to negative longitudes (west of 180°) - A naive rendering connects the last point east of the dateline (e.g., 179.97) to the first point west of the dateline (e.g., -179.51) going the long way around - The fix: when points cross 180°, we can normalize coordinates so they're continuous One approach: 1. For each feature, check if it crosses the antimeridian 2. If it does, split the LineString at the antimeridian into segments 3. For coordinates on the "west" side (negative longitudes), add 360 to them to make them continuous 4. Then after projecting, the segments will be separate parts of a MultiLineString Let me think about this more carefully. For T001, the coordinates in longitude order are: 178.94, 179.46, 179.97, -179.51, -179.00, -178.48 So the path goes eastward from ~179°E across the date line to ~179°W (which is 181°E in continuous coordinates), then continues westward to ~178°W (182°E). If we add 360 to the negative longitudes: 178.94, 179.46, 179.97, 180.49, 181.00, 181.52 But that creates one continuous line. However, the problem is about rendering - we need to split it into segments that don't cross the antimeridian. Actually, the best approach is: For features crossing the antimeridian, I should: 1. Identify where the longitude jumps across the antimeridian (from ~179/+ to ~-179/- or vice versa) 2. Split at those points 3. For the segments on each side, keep original coordinates 4. Create a MultiLineString with parts on each side of the antimeridian Then to calculate length in metres, project each part to a suitable CRS and calculate. Let me write a Python script. First, let me check what CRS to use for Fiji's national metric grid. I'll use pyproj to look up available CRS for Fiji.
0:30
0:30
Bash
python3 -c "
python3 -c "
from pyproj import CRS
# Fiji Map Grid
crs = CRS.from_epsg(3460)
print(crs)
print('---')
# Also check EPSG:3139
crs2 = CRS.from_epsg(3139)
print(crs2)
print('---')
crs3 = CRS.from_epsg(2120)
print(crs3)
"
EPSG:3460 --- EPSG:3139 --- EPSG:2120
0:37
Let me check Fiji Map Grid - EPSG:3460 is "Fiji 1956 / Fiji Map Grid" which seems like the right one. But let me also check EPSG:2138 - "Fiji 1956 / UTM zone 60S" or "Fiji 1956 / UTM zone 1S". Actually, the Fiji Map Grid is EPSG:3460 (Fiji 1956 / Fiji Map Grid). Let me verify. Actually, Fiji's national metric grid is likely "Fiji 1956 / Fiji Map Grid" (EPSG:3460) or "Fiji 1986 / Fiji Map Grid" (EPSG:3139). Let me check more. Wait, the user said "Fiji's national metric grid". The most standard one is EPSG:3460 (Fiji 1956 / Fiji Map Grid). But common modern one is EPSG:3139 (Fiji 1986 / Fiji Map Grid). Let me check what's available and commonly used.
0:37
Bash
python3 -c "
python3 -c "
from pyproj import CRS
# Check details
for e in [3460, 3139, 2120, 2138, 2139]:
c = CRS.from_epsg(e)
print(f'EPSG:{e} - {c.name}')
"
EPSG:3460 - Fiji 1986 / Fiji Map Grid EPSG:3139 - Vanua Levu 1915 / Vanua Levu Grid EPSG:2120 - NZGD2000 / Marlborough 2000 EPSG:2138 - NAD27(CGQ77) / Quebec Lambert EPSG:2139 - NAD83(CSRS98) / SCoPQ zone 2
1:16
EPSG:3460 is "Fiji 1986 / Fiji Map Grid" - that's Fiji's national metric grid. Let me write the solution.
Now, the issue with the geometries: transects that cross the antimeridian (the 180° longitude line) have coordinates that go from positive (e.g. 179.9°) to negative (e.g. -179.8°). In a naive rendering, these would connect across the entire globe instead of going the short way across the dateline.
The solution: I need to split these antimeridian-crossing lines at the dateline (180° longitude). For each segment that crosses from one side to the other, I need to split it and create separate parts on each side.
Let me think about the approach:
1. For each feature, check if it crosses the antimeridian (or use the flag)
2. If it does, split the line at the antimeridian (180° longitude)
3. Then reproject to Fiji Map Grid (EPSG:3460)
4. Calculate length
5. Output as MultiLineString
Actually, a simpler approach:
- Shift longitudes that are near the antimeridian: for segments crossing the dateline, I can add/subtract 360 to make them continuous, then split.
Let me think more carefully. The problem is coordinates like [179.9, ...] followed by [-179.9, ...]. If I add 360 to the negative values, I get continuous longitudes. Then I need to split at the 180° meridian.
Actually, the standard approach for antimeridian crossing:
1. For each pair of consecutive points, check if they cross the antimeridian (i.e., one has lon near +180 and other near -180, with a large gap)
2. If so, interpolate the crossing point at lon=180
3. Split the linestring into two parts: one on each side
4. Shift the eastern side's longitudes by -360 to get them back to normal, or shift the western side's by +360
Wait, a better approach:
- For each linestring, iterate through coordinates.
- If a segment crosses the antimeridian (lon diff > 180 in absolute value), compute intersection with the 180° meridian.
- Create two separate linestrings: one for the eastern side (longitudes > 0, but for the crossing part, up to 180) and one for the western side (longitudes < 0, from -180 onward).
Let me think about the algorithm more carefully.
For a line crossing from east to west (e.g., 179.9 -> -179.9):
1. The crossing point at 180° longitude can be interpolated.
2. Part 1: from start to the crossing point (east side)
3. Part 2: from crossing point to end (west side)
But I also need to handle the case where the line goes from west to east (e.g., -179.9 -> 179.9), though in the data I see the antimeridian-crossing ones go east->west.
Let me write a comprehensive solution.
Actually, let me use the `shapely.ops.transform` and `shapely.ops.split` approach, or use a technique with `shapely.set_precision` or manual splitting.
Let me write a Python script:
```python
import json
import geopandas as gpd
import shapely.geometry as geom
from shapely.ops import transform
from pyproj import CRS, Transformer
from math import isclose
# Read input
with open('/work/fiji_transects_wgs84.geojson') as f:
data = json.load(f)
# Fiji Map Grid
fmg_crs = CRS.from_epsg(3460)
wgs84_crs = CRS.from_epsg(4326)
transformer = Transformer.from_crs(wgs84_crs, fmg_crs, always_xy=True)
def normalize_lon(lon):
"""Normalize to -180..180"""
return ((lon + 180) % 360) - 180
def split_at_antimeridian(coords):
"""
Split a list of coordinates into parts that don't cross the antimeridian.
Returns list of lists of coordinates.
"""
parts = []
current_part = [coords[0]]
for i in range(1, len(coords)):
prev_lon, prev_lat = coords[i-1]
cur_lon, cur_lat = coords[i]
# Check if the segment crosses the antimeridian
# (the difference in longitude is > 180 degrees in absolute value)
lon_diff = abs(cur_lon - prev_lon)
if lon_diff > 180:
# It crosses. Find the intersection point at lon=180
# Using linear interpolation
# If prev_lon < cur_lon, we're going west->east (crossing -180), else east->west (crossing 180)
# Determine which direction we're crossing
if prev_lon < 0 and cur_lon > 0: # crossing from west to east (across -180)
# Actually if prev_lon is like -179.9 and cur_lon is 179.9,
# the crossing is at lon=180 (or lon=-180, same point)
# The segment goes from prev_lon to (cur_lon - 360)
adj_cur_lon = cur_lon - 360
# Find t where lon = 180 (but we're going from prev_lon < 0 to adj_cur_lon which is < 0 too... hmm)
# Actually, going from -179.9 to 179.9: the shortest path goes through lon=180
# prev_lon = -179.9, cur_lon = 179.9
# adj_cur_lon = -180.1
# The line goes from -179.9 to -180.1 crossing lon=180... wait that doesn't work either.
# Let's think differently. We're at prev_lon (e.g. -179.9) and want to go to cur_lon (179.9).
# The shortest path goes through lon=180 (going eastward from -179.9 to 180, then to 179.9).
# The crossing point at lon=180: we need to interpolate.
# Going eastward: prev_lon to +180, then wrap to -180 and go to cur_lon.
# Actually cur_lon = 179.9, which is closer to 180 through the positive side.
# So the path is: prev_lon (-179.9) -> 180 -> 179.9
# The crossing point is at lon=180.
pass
elif prev_lon > 0 and cur_lon < 0: # crossing from east to west (across 180)
# e.g. prev_lon=179.9, cur_lon=-179.9
# Going eastward: 179.9 -> 180 -> -179.9... no, eastward from 179.9 goes to 180, then -180, then -179.9
# Actually the shortest path from 179.9 to -179.9 goes through lon=180/-180.
pass
# Let me use a simpler approach
# The crossing is at lon=180 (or lon=-180, same meridian)
# Interpolate the latitude at lon=180
# We need to handle two directions:
# Case 1: prev_lon is positive (~179.x), cur_lon is negative (~-179.x) - crossing 180 going east to west
# Case 2: prev_lon is negative (~-179.x), cur_lon is positive (~179.x) - crossing 180 going west to east
# For Case 1: prev_lon -> +180, then -180 -> cur_lon
# For Case 2: prev_lon -> -180, then +180 -> cur_lon (or equivalently prev_lon -> +180, then -180 -> cur_lon)
# Actually the meridian is the same whether we call it 180 or -180.
# Let me adjust one of the longitudes by +/- 360 to make the segment not wrap
if prev_lon > 0 and cur_lon < 0:
# Going east to west: adjust cur_lon by +360
adj_cur_lon = cur_lon + 360 # e.g., -179.9 + 360 = 180.1
# Now segment goes from prev_lon (~179.9) to adj_cur_lon (~180.1)
# Crossing at lon=180
t = (180 - prev_lon) / (adj_cur_lon - prev_lon)
crossing_lat = prev_lat + t * (cur_lat - prev_lat)
# Part 1: from start to crossing (east side, lon around 180)
# Part 2: from crossing to end (west side, lon around -180)
pass
elif prev_lon < 0 and cur_lon > 0:
# Going west to east: adjust cur_lon by -360
adj_cur_lon = cur_lon - 360 # e.g., 179.9 - 360 = -180.1
# Now segment goes from prev_lon (~-179.9) to adj_cur_lon (~-180.1)
# Crossing at lon=-180 (same as 180)
t = (-180 - prev_lon) / (adj_cur_lon - prev_lon)
crossing_lat = prev_lat + t * (cur_lat - prev_lat)
# Part 1: from start to crossing (west side, lon around -180)
# Part 2: from crossing to end (east side, lon around 180)
pass
# Finish current part with crossing point
crossing_point = (180 if prev_lon > 0 else -180, crossing_lat)
# Actually this is getting complicated. Let me use a different approach.
```
OK, let me think of a cleaner algorithm.
Actually, the simplest approach I know of for handling antimeridian crossing:
1. Start with the line's coordinates.
2. For each consecutive pair, check if the longitudinal gap is > 180 degrees (in absolute value).
3. If so, we need to split. Compute the intersection with the 180° meridian.
Let me think about it more systematically with a concrete example:
T001 coordinates (in order):
[178.94, -17.63], [179.46, -17.62], [179.97, -17.61], [-179.51, -17.60], [-179.00, -17.58], [-178.48, -17.58]
So the transition from [179.97, -17.61] to [-179.51, -17.60] crosses the antimeridian.
Going from 179.97 to -179.51: the shortest path is through 180, going eastward.
- Starting at ~180° (179.97), go to 180°, then wrap to -180°, then to -179.51.
- So the crossing point is at (180, -17.605...).
For the split:
- Part 1: [178.94, -17.63], [179.46, -17.62], [179.97, -17.61], (180, crossing_lat)
- Part 2: (-180, crossing_lat), [-179.51, -17.60], [-179.00, -17.58], [-178.48, -17.58]
But wait, Part 2 starts at -180 which is the same as 180. And the coordinate [-179.51, -17.60] is correct on the west side.
Then when reprojecting to Fiji Map Grid (EPSG:3460), both parts should be fine.
Let me write the code more carefully.
```python
import json
import geopandas as gpd
import numpy as np
from shapely.geometry import LineString, MultiLineString, Point
from shapely.ops import transform
from pyproj import CRS, Transformer
import math
def split_line_at_antimeridian(line_coords):
"""Split a LineString's coordinates at the antimeridian (180°/-180° longitude).
Returns a list of coordinate lists, one for each part."""
parts = []
current_part = [list(line_coords[0])]
for i in range(1, len(line_coords)):
prev = line_coords[i-1]
cur = line_coords[i]
# Check if segment crosses antimeridian (longitude gap > 180 degrees)
if abs(cur[0] - prev[0]) > 180:
# Determine direction
if prev[0] > 0 and cur[0] < 0:
# East to west: segment crosses 180° going east-to-west
# Adjusted cur longitude for interpolation
adj_cur = (cur[0] + 360, cur[1])
# Interpolate where lon=180
t = (180 - prev[0]) / (adj_cur[0] - prev[0])
crossing_lat = prev[1] + t * (cur[1] - prev[1])
# End current part at crossing point (180° side)
current_part.append([180, crossing_lat])
parts.append(current_part)
# Start new part at crossing point (-180° side)
current_part = [[-180, crossing_lat], list(cur)]
else:
# West to east: segment crosses -180° (180°) going west-to-east
adj_cur = (cur[0] - 360, cur[1])
t = (-180 - prev[0]) / (adj_cur[0] - prev[0])
crossing_lat = prev[1] + t * (cur[1] - prev[1])
# End current part at crossing point (-180° side)
current_part.append([-180, crossing_lat])
parts.append(current_part)
# Start new part at crossing point (180° side)
current_part = [[180, crossing_lat], list(cur)]
else:
current_part.append(list(cur))
parts.append(current_part)
return parts
```
This should work! Let me also handle cases where lines extend further east past 180 or west past -180, but for the Fiji data, the coordinates should be in the -180..180 range already.
Actually wait - I need to check the T004 transect. Its coordinates go:
[178.87, -17.80], [179.54, -17.60], [-179.79, -17.41], [-179.12, -17.19], [-178.45, -16.99], [-177.78, -16.80]
So it crosses the antimeridian between [179.54, -17.60] and [-179.79, -17.41]. Going east-to-west.
Let me write the full script now.
For the Fiji Map Grid, I'll use EPSG:3460.
Let me also think about whether I need to handle the case where after splitting, the parts need to be valid geojson with coordinates in the -180..180 range. Yes, the parts I produce have coordinates in the correct range.
After reprojection to FMG, I'll create a MultiLineString if there's more than one part, or a LineString if there's only one (but the instructions say to output MultiLineString for all features).
Actually the instructions say: "Every feature must come out as a MultiLineString, so do not leave any transects as plain LineString". So I'll wrap everything in MultiLineString.
Let me write the script.
1:16
1:16
Write
/work/solve.py
content · 139 lines · py
import json
from shapely.geometry import LineString, MultiLineString, shape
from shapely.ops import transform
from pyproj import CRS, Transformer
import math
# ------------------------------------------------------------
# 1. Read input
# ------------------------------------------------------------
with open('/work/fiji_transects_wgs84.geojson') as f:
raw = json.load(f)
features = raw["features"]
# ------------------------------------------------------------
# 2. CRS set-up
# ------------------------------------------------------------
wgs84 = CRS.from_epsg(4326)
fmg = CRS.from_epsg(3460) # Fiji Map Grid (metres)
tfm = Transformer.from_crs(wgs84, fmg, always_xy=True).transform
# ------------------------------------------------------------
# 3. Helper: split a coordinate list at the antimeridian (180°)
# Returns list of coordinate-lists, one per part.
# ------------------------------------------------------------
def split_at_antimeridian(coords):
"""
coords : list of [lon, lat] pairs (in -180..180).
Returns list of lists-of-pairs, each part not crossing the antimeridian.
"""
parts = []
current = [list(coords[0])]
for i in range(1, len(coords)):
prev = coords[i - 1]
cur = coords[i]
lon_diff = abs(cur[0] - prev[0])
if lon_diff > 180.0:
# ----- segment crosses the antimeridian -----
if prev[0] > 0 and cur[0] < 0:
# East → West: crossing the 180° meridian
# Adjust cur longitude by +360 so segment is continuous
adj_cur = (cur[0] + 360.0, cur[1])
# Interpolate where lon = 180
t = (180.0 - prev[0]) / (adj_cur[0] - prev[0])
xing_lat = prev[1] + t * (cur[1] - prev[1])
# close current part on the +180 side
current.append([180.0, xing_lat])
parts.append(current)
# start new part on the -180 side
current = [[-180.0, xing_lat], list(cur)]
elif prev[0] < 0 and cur[0] > 0:
# West → East: crossing the -180° meridian
adj_cur = (cur[0] - 360.0, cur[1])
t = (-180.0 - prev[0]) / (adj_cur[0] - prev[0])
xing_lat = prev[1] + t * (cur[1] - prev[1])
current.append([-180.0, xing_lat])
parts.append(current)
current = [[180.0, xing_lat], list(cur)]
else:
# Shouldn't happen for normal Fiji data, but be safe
current.append(list(cur))
else:
# No crossing – just continue
current.append(list(cur))
parts.append(current)
return parts
# ------------------------------------------------------------
# 4. Process every feature
# ------------------------------------------------------------
out_features = []
for feat in features:
props = feat["properties"]
geom = shape(feat["geometry"])
coords = list(geom.coords)
# Split at antimeridian if needed
parts_coords = split_at_antimeridian(coords)
# Build individual LineStrings
line_strings = []
for pts in parts_coords:
ls = LineString(pts)
# Reproject to FMG
ls_fmg = transform(tfm, ls)
line_strings.append(ls_fmg)
# Combine into MultiLineString
mls = MultiLineString(line_strings)
# Calculate total length (metres) – sum of part lengths
length_m = sum(ls.length for ls in line_strings)
out_feat = {
"type": "Feature",
"properties": {
"transect_id": props["transect_id"],
"vessel": props["vessel"],
"survey_date": props["survey_date"],
"length_m": round(length_m, 2)
},
"geometry": {
"type": "MultiLineString",
"coordinates": [list(ls.coords) for ls in line_strings]
}
}
out_features.append(out_feat)
# ------------------------------------------------------------
# 5. Write output GeoJSON
# ------------------------------------------------------------
out_collection = {
"type": "FeatureCollection",
"name": "fiji_transects_fmg",
"crs": {
"type": "name",
"properties": {"name": "urn:ogc:def:crs:EPSG::3460"}
},
"features": out_features
}
with open("/work/fiji_transects_fmg.geojson", "w") as f:
json.dump(out_collection, f, indent=2)
print(f"Wrote {len(out_features)} features to /work/fiji_transects_fmg.geojson")Wrote /work/solve.py (4539 chars).
1:19
Let me run it and check the output.
1:19
Bash
cd /work && python3 solve.py
Wrote 30 features to /work/fiji_transects_fmg.geojson
1:23
Let me verify the output by reading it and checking some key transects.
1:23
Read
/work/fiji_transects_fmg.geojson
1 {
2 "type": "FeatureCollection",
3 "name": "fiji_transects_fmg",
4 "crs": {
5 "type": "name",
6 "properties": {
7 "name": "urn:ogc:def:crs:EPSG::3460"
8 }
9 },
10 "features": [
11 {
12 "type": "Feature",
13 "properties": {
14 "transect_id": "T001",
15 "vessel": "Taveuni II",
16 "survey_date": "2025-08-15",
17 "length_m": 273335.11
18 },
19 "geometry": {
20 "type": "MultiLineString",
21 "coordinates": [
22 [
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65 "vessel": "Bligh",
66 "survey_date": "2025-08-12",
67 "length_m": 216575.29
68 },
69 "geometry": {
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107 "vessel": "Lomaiviti",
108 "survey_date": "2025-08-12",
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110 },
111 "geometry": {
112 "type": "MultiLineString",
113 "coordinates": [
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153 "vessel": "Vanua I",
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155 "length_m": 372666.09
156 },
157 "geometry": {
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207 "geometry": {
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253 {
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257 "vessel": "Cakaulevu",
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261 "geometry": {
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405 }
406 },
407 {
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1:54
Let me verify the output looks correct. Let me check a few things: 1. All features are MultiLineString ✓ 2. The antimeridian-crossing features (T001-T010) have been split into multiple parts ✓ 3. The non-antimeridian features (T011-T030) should ideally also be MultiLineString but might show with a single part - let me check that's the case. Wait, looking at the output more carefully, I notice something potentially wrong with the antimeridian handling. Let me look at T001: Original coordinates: [178.94, -17.63], [179.46, -17.62], [179.97, -17.61], [-179.51, -17.60], [-178.99, -17.58], [-178.48, -17.58] The split happens between [179.97, -17.61] and [-179.51, -17.60]. The algorithm: 1. prev=[179.97, -17.61], cur=[-179.51, -17.60] 2. prev[0] > 0 and cur[0] < 0 → East to West crossing 3. adj_cur = (-179.51 + 360, -17.60) = (180.49, -17.60) 4. t = (180 - 179.97) / (180.49 - 179.97) = 0.03 / 0.52 ≈ 0.0577 5. xing_lat = -17.61 + 0.0577 * (-17.60 - (-17.61)) = -17.61 + 0.0577 * 0.01 = -17.6094... So current part 1 gets [..., [180.0, -17.6094]] And part 2 gets [[-180.0, -17.6094], [-179.51, -17.60], ...] Then when reprojecting to FMG: - For part 1: coords are [178.94, -17.63], [179.46, -17.62], [179.97, -17.61], [180.0, -17.6094] → these are all in the "east" side, should project fine - For part 2: coords are [-180.0, -17.6094], [-179.51, -17.60], [-178.99, -17.58], [-178.48, -17.58] → these are all in the "west" side, should project fine Wait, but there's a problem. The reprojection happens using the actual longitude values (-180.0, not 180.0). Let me check what EPSG:3460's area of use is. Fiji 1986 / Fiji Map Grid covers Fiji islands which span from about 177°E to 179°W. So coordinates like 180° or -180° might be at the edge of the projection or problematic. Actually, Fiji Map Grid should handle coordinates in the Fiji area fine. The coordinates at 180° and -180° are both at the antimeridian but the projection should handle them. Let me verify by checking the projection bounds. Actually, looking at the output for T001: Part 1 coordinates (FM reprojected): [2020343, 3930017], [2074969, 3930832], [2129608, 3931959], [2132641, 3932030] Part 2 coordinates (FM reprojected): [2132641, 3932030], [2184265, 3933178], [2238946, 3934438], [2293630, 3933970] The two parts meet at [2132641, 3932030] which is consistent - the insertion point matches. Good. But wait - the issue might be that points at exactly 180.0 or -180.0 might not project correctly with EPSG:3460. Let me verify quickly. Actually, EPSG:3460 (Fiji 1986 / Fiji Map Grid) has this projection: - Projection: Transverse Mercator - Central meridian: 178°E - False easting: 2,000,000 m - False northing: 0 m So a point at lon=180° would be 2° east of the central meridian, which should be fine. But wait, I think there might be a subtle issue. When we split, we insert [180.0, xing_lat] at the end of part 1 and [-180.0, xing_lat] at the start of part 2. But these are the same geographic point - just expressed differently. When projected to FMG, they should come out as the same coordinates (or very close). Let me check T001 output: Part 1 last coord: [2132641.3519591475, 3932030.6236885176] Part 2 first coord: [2132641.3519591503, 3932030.6236885176] Those are very slightly different (1e-12 difference in x) due to floating point. That's fine. Now for the non-antimeridian features - they should still be MultiLineString but with a single part. Let me check T011: Yes, it has a single array of coordinates wrapped in another array. That's correct MultiLineString with one line. Wait, I need to double check something though. For the features that cross the antimeridian, the split_at_antimeridian function adds an extra vertex at 180°/-180°. But the original features already have vertices crossing the antimeridian. Let me trace through T001 more carefully. Original T001 coords (lon, lat): [178.941879580782086, -17.632301816020771] [179.456655009654696, -17.623768593111961] [179.971430438527307, -17.611072392823225] [-179.513794132600054, -17.596198176111951] [-178.999018703727444, -17.579632069513806] [-178.484243274854833, -17.577321872344196] Step 0: i=0, no split, current = [[178.94..., -17.63...]] Step 1: i=1, prev=[178.94...], cur=[179.46...], lon_diff=0.51 < 180, no split. current = [[178.94..., -17.63...], [179.46..., -17.62...]] Step 2: i=2, prev=[179.46...], cur=[179.97...], lon_diff=0.51 < 180, no split. current = [[178.94...], [179.46...], [179.97...]] Step 3: i=3, prev=[179.97...], cur=[-179.51...], lon_diff=359.48 > 180. prev[0] > 0 and cur[0] < 0 → East→West crossing. adj_cur = (-179.51 + 360, -17.60) = (180.49, -17.60) t = (180 - 179.97) / (180.49 - 179.97) = 0.03/0.52 = 0.0577 xing_lat = -17.611 + 0.0577 * (-17.596 - (-17.611)) = -17.611 + 0.0577 * 0.015 = -17.6101 current becomes [[178.94...], [179.46...], [179.97...], [180.0, -17.6101]] parts = [current] current = [[-180.0, -17.6101], [-179.51..., -17.60...]] Step 4: i=4, prev=[-179.51...], cur=[-178.99...], lon_diff=0.51 < 180. current = [[-180.0], [-179.51], [-178.99]] Step 5: i=5, prev=[-178.99...], cur=[-178.48...], lon_diff=0.51 < 180. current = [[-180.0], [-179.51], [-178.99], [-178.48]] End: parts = [part1, part2] This looks correct! The antimeridian features are properly split into two parts. Now let me also check that all features are MultiLineString. Looking at the output, each geometry has type "MultiLineString" with coordinates being an array of arrays. For single-part features (like T011), it's a single array wrapped in an outer array. That's valid GeoJSON MultiLineString. Everything looks good. The output file is at `/work/fiji_transects_fmg.geojson` as requested.
1:54
1:54
Bash
cd /work && python3 -c "
cd /work && python3 -c "
import json
with open('fiji_transects_fmg.geojson') as f:
data = json.load(f)
print(f'Number of features: {len(data[\"features\"])}')
print(f'CRS: {data[\"crs\"]}')
for feat in data['features']:
props = feat['properties']
gtype = feat['geometry']['type']
n_parts = len(feat['geometry']['coordinates'])
tid = props['transect_id']
print(f'{tid}: type={gtype}, parts={n_parts}, length_m={props[\"length_m\"]}, vessel={props[\"vessel\"]}, survey_date={props[\"survey_date\"]}')
"
Number of features: 30
CRS: {'type': 'name', 'properties': {'name': 'urn:ogc:def:crs:EPSG::3460'}}
T001: type=MultiLineString, parts=2, length_m=273335.11, vessel=Taveuni II, survey_date=2025-08-15
T002: type=MultiLineString, parts=2, length_m=216575.29, vessel=Bligh, survey_date=2025-08-12
T003: type=MultiLineString, parts=2, length_m=351823.46, vessel=Lomaiviti, survey_date=2025-08-12
T004: type=MultiLineString, parts=2, length_m=372666.09, vessel=Vanua I, survey_date=2025-08-15
T005: type=MultiLineString, parts=2, length_m=362394.57, vessel=Bligh, survey_date=2025-08-19
T006: type=MultiLineString, parts=2, length_m=393605.56, vessel=Cakaulevu, survey_date=2025-08-13
T007: type=MultiLineString, parts=2, length_m=414594.38, vessel=Vanua I, survey_date=2025-08-19
T008: type=MultiLineString, parts=2, length_m=146792.55, vessel=Taveuni II, survey_date=2025-08-12
T009: type=MultiLineString, parts=2, length_m=263388.29, vessel=Vanua I, survey_date=2025-08-13
T010: type=MultiLineString, parts=2, length_m=489842.48, vessel=Vanua I, survey_date=2025-08-15
T011: type=MultiLineString, parts=1, length_m=78492.17, vessel=Taveuni II, survey_date=2025-08-20
T012: type=MultiLineString, parts=1, length_m=84537.56, vessel=Taveuni II, survey_date=2025-08-20
T013: type=MultiLineString, parts=1, length_m=179800.48, vessel=Bligh, survey_date=2025-08-19
T014: type=MultiLineString, parts=1, length_m=148392.88, vessel=Lomaiviti, survey_date=2025-08-13
T015: type=MultiLineString, parts=1, length_m=124738.16, vessel=Vanua I, survey_date=2025-08-15
T016: type=MultiLineString, parts=1, length_m=53310.24, vessel=Taveuni II, survey_date=2025-08-15
T017: type=MultiLineString, parts=1, length_m=152432.38, vessel=Taveuni II, survey_date=2025-08-12
T018: type=MultiLineString, parts=1, length_m=112421.62, vessel=Bligh, survey_date=2025-08-19
T019: type=MultiLineString, parts=1, length_m=179435.73, vessel=Lomaiviti, survey_date=2025-08-12
T020: type=MultiLineString, parts=1, length_m=215352.23, vessel=Taveuni II, survey_date=2025-08-13
T021: type=MultiLineString, parts=1, length_m=230219.24, vessel=Vanua I, survey_date=2025-08-16
T022: type=MultiLineString, parts=1, length_m=50981.78, vessel=Vanua I, survey_date=2025-08-15
T023: type=MultiLineString, parts=1, length_m=81980.09, vessel=Lomaiviti, survey_date=2025-08-12
T024: type=MultiLineString, parts=1, length_m=251074.91, vessel=Vanua I, survey_date=2025-08-12
T025: type=MultiLineString, parts=1, length_m=108459.05, vessel=Taveuni II, survey_date=2025-08-19
T026: type=MultiLineString, parts=1, length_m=100661.48, vessel=Cakaulevu, survey_date=2025-08-19
T027: type=MultiLineString, parts=1, length_m=130089.67, vessel=Vanua I, survey_date=2025-08-12
T028: type=MultiLineString, parts=1, length_m=173047.04, vessel=Vanua I, survey_date=2025-08-12
T029: type=MultiLineString, parts=1, length_m=205262.64, vessel=Lomaiviti, survey_date=2025-08-19
T030: type=MultiLineString, parts=1, length_m=163829.39, vessel=Cakaulevu, survey_date=2025-08-19
2:01
The results look good. Let me verify that: 1. All 30 features are present 2. All are MultiLineString type 3. The antimeridian-crossing transects (T001-T010) have 2 parts each (split properly) 4. The non-crossing transects (T011-T030) have 1 part each 5. Every feature has transect_id, vessel, survey_date, and length_m 6. The CRS is EPSG:3460 (Fiji Map Grid) Everything checks out. Let me do one final validation to make sure the GeoJSON is valid.
2:01
Bash
cd /work && python3 -c "
cd /work && python3 -c "
import json, sys
with open('fiji_transects_fmg.geojson') as f:
data = json.load(f)
# Basic GeoJSON conformance checks
assert data['type'] == 'FeatureCollection'
for feat in data['features']:
assert feat['type'] == 'Feature'
assert feat['geometry']['type'] == 'MultiLineString'
assert feat['geometry']['coordinates']
props = feat['properties']
for key in ['transect_id', 'vessel', 'survey_date', 'length_m']:
assert key in props
# Check coordinates are 3-4 digit precision EPSG:3460 values (metres)
for part in feat['geometry']['coordinates']:
for coord in part:
assert len(coord) == 2
assert isinstance(coord[0], (int, float))
assert isinstance(coord[1], (int, float))
print('All validations passed!')
"
All validations passed!
2:15
Everything looks good. Let me summarize what was done: 1. **Problem**: The antimeridian-crossing transects (T001-T010) had coordinates crossing the 180° line, which caused rendering engines to draw arcs spanning the entire globe instead of short local segments. 2. **Solution**: - I wrote a `split_at_antimeridian()` function that detects when a segment crosses the 180° meridian (longitude difference > 180°, or sign change) and splits the line at the antimeridian. - When crossing from East to West (e.g., +179° → -179°), it interpolates the crossing point at longitude +180°/-180°, closes the first part, and starts a new part on the other side. - Each part becomes a separate LineString within a MultiLineString. - All features are converted to MultiLineString (even non-crossing ones become single-part MultiLineString). - The geometry is reprojected from WGS84 (EPSG:4326) to Fiji Map Grid (EPSG:3460) in metres. - Each feature gets a `length_m` attribute (sum of part lengths in metres). - Original `transect_id`, `vessel`, and `survey_date` are preserved. 3. **Results**: - 30 features, all MultiLineString type - T001-T010 (antimeridian-crossing) each have 2 parts - T011-T030 (non-crossing) each have 1 part - Lengths computed in metres - CRS set to `urn:ogc:def:crs:EPSG::3460`
2:15