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": "google/gemma-4-26b-a4b-it",
"base_url": "https://openrouter.ai/api/v1"
}
0:01
Bash
ls -F
fiji_transects_wgs84.geojson
0:02
Read
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 ] ] } },
<system-reminder>Showed lines 1-20 of 37. Re-call Read with offset=21 to continue, or raise limit.</system-reminder>
0:25
Write
solve.py
content · 131 lines · py
import geopandas as gpd
import pandas as pd
from shapely.geometry import LineString, MultiLineString
from shapely.ops import split, transform
import pyproj
def fix_antimeridian_lines(line, lon_range=(170, -170)):
"""
Splits a LineString that crosses the antimeridian into multiple LineStrings.
"""
coords = list(line.coords)
new_parts = []
current_part_coords = []
for i in range(len(coords)):
lon, lat = coords[i]
if i > 0:
prev_lon, prev_lat = coords[i-1]
# Check for wrap-around.
# A wrap-around is detected if the jump in longitude is large.
# Since these are local segments, a jump > 180 degrees indicates a wrap.
if abs(lon - prev_lon) > 180:
# Close current part
if current_part_coords:
new_parts.append(LineString(current_part_coords))
current_part_coords = []
# Adjust longitude of the current point to be on the "other side"
if lon < prev_lon: # jump from e.g. 179 to -179
new_lon = lon + 360
else: # jump from e.g. -179 to 179
new_lon = lon - 360
current_part_coords.append((new_lon, lat))
else:
current_part_coords.append((lon, lat))
else:
current_part_coords.append((lon, lat))
if current_part_coords:
new_parts.append(LineString(current_part_coords))
if not new_parts:
return line
# If multiple parts, return MultiLineString, else LineString (but user wants MultiLineString)
if len(new_parts) == 1:
return MultiLineString([new_parts[0]])
else:
return MultiLineString(new_parts)
def main():
input_file = 'fiji_transects_wgs84.geojson'
output_file = 'fiji_transects_fmg.geojson'
# Fiji National Grid (FMG) is often Fiji Transverse Mercator.
# EPSG:2977 is Fiji Transverse Mercator (Fiji Grid).
# Let's use a common metric projection if specific FMG isn't standard in pyproj.
# Looking up Fiji CRS: EPSG:2977 is widely used.
fiji_crs = "EPSG:2977"
gdf = gpd.read_file(input_file)
# 1. Fix Antimeridian geometries
# We'll create a new geometry column
new_geoms = []
for geom in gdf.geometry:
if geom.geom_type == 'LineString':
# Split it
fixed_geom = fix_antimeridian_lines(geom)
new_geoms.append(fixed_geom)
elif geom.geom_type == 'MultiLineString':
# If it's already MultiLineString, we treat it as a collection of lines
# or just try to fix each part.
parts = []
for part in geom.geoms:
parts.append(fix_antimeridian_lines(part))
new_geoms.append(MultiLineString(parts))
else:
new_geoms.append(geom)
gdf.geometry = new_geoms
# 2. Convert to MultiLineString for EVERYTHING
# The prompt says: "Every feature must come out as a MultiLineString"
final_geoms = []
for geom in gdf.geometry:
if geom.geom_type == 'LineString':
final_geoms.append(MultiLineString([geom]))
else:
final_geoms.append(geom)
gdf.geometry = final_geoms
# 3. Transform to Fiji metric grid (EPSG:2977)
# We need to calculate lengths in the metric CRS.
# To preserve the "broken" parts but keep them as one feature (MultiLineString),
# we should transform the geometry to the metric CRS.
# Note: When we transform from WGS84 (with jumps) to a metric CRS,
# we must ensure the coordinates are "continuous" in longitude space first.
# The fix_antimeridian_lines function already adjusted longitudes (e.g. 179 -> 181).
# This is good because it makes the geometry continuous for projection.
gdf_metric = gdf.to_crs(fiji_crs)
# 4. Calculate length_m
gdf_metric['length_m'] = gdf_metric.geometry.length
# 5. Ensure attributes are carried through
# The prompt says "carry the survey attributes (vessel and survey_date) through unchanged"
# and "use transect_id as the key field".
# We should ensure we don't have extra columns like 'crosses_antimeridian_flag' if not needed,
# but usually "carry through" means keep them.
# Re-order/select columns if necessary, but generally keeping them is fine.
# The user wants transect_id, vessel, survey_date, and length_m.
# 6. Output as GeoJSON
# Note: GeoJSON is typically WGS84. However, the prompt asks to "convert them to Fiji's national metric grid"
# and "write the result as GeoJSON".
# Usually, GeoJSON is forced to WGS84 by many tools.
# But if the user wants the *coordinates* in metric, we should write it out.
# To force GeoJSON to not auto-convert back to WGS84, we can specify the CRS in the output.
gdf_metric.to_file(output_file, driver='GeoJSON')
print(f"Successfully wrote {len(gdf_metric)} features to {output_file}")
if __name__ == "__main__":
main()
Wrote solve.py (5171 chars).
0:26
Bash
python solve.py
Successfully wrote 30 features to fiji_transects_fmg.geojson
0:28
Read
fiji_transects_fmg.geojson
1 {
2 "type": "FeatureCollection",
3 "name": "fiji_transects_fmg",
4 "crs": { "type": "name", "properties": { "name": "urn:ogc:def:crs:EPSG::2977" } },
5 "features": [
6 { "type": "Feature", "properties": { "transect_id": "T001", "vessel": "Taveuni II", "survey_date": "2025-08-15T00:00:00", "crosses_antimeridian_flag": true, "length_m": 242148.17462422571 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2577818.856368530075997, 7808045.933654122054577 ], [ -2517744.839244871865958, 7818720.514956817030907 ], [ -2457959.618174184113741, 7829649.209022815339267 ] ], [ [ -2398415.969535397831351, 7840591.110509934835136 ], [ -2339097.41476799082011, 7851489.390455325134099 ], [ -2279720.962942078709602, 7860430.453650631010532 ] ] ] } },
7 { "type": "Feature", "properties": { "transect_id": "T002", "vessel": "Bligh", "survey_date": "2025-08-12T00:00:00", "crosses_antimeridian_flag": true, "length_m": 160320.4850304015 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2568571.367820397950709, 7846831.475579218938947 ], [ -2494815.333217027131468, 7878702.454537282697856 ] ], [ [ -2421194.358998955693096, 7910035.447528526186943 ], [ -2347860.87270077271387, 7941939.787312176078558 ] ] ] } },
8 { "type": "Feature", "properties": { "transect_id": "T003", "vessel": "Lomaiviti", "survey_date": "2025-08-12T00:00:00", "crosses_antimeridian_flag": true, "length_m": 294940.81524540769 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2737259.021241321694106, 7816272.578033835627139 ], [ -2638431.858519812580198, 7825394.063890357501805 ], [ -2540319.581941521726549, 7834153.894859520718455 ] ], [ [ -2442858.046751122921705, 7842329.020383344963193 ], [ -2345905.603365982417017, 7849135.118691245093942 ] ] ] } },
9 { "type": "Feature", "properties": { "transect_id": "T004", "vessel": "Vanua I", "survey_date": "2025-08-15T00:00:00", "crosses_antimeridian_flag": true, "length_m": 329398.56369994534 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2582407.215880405623466, 7785839.181658865883946 ], [ -2508233.587048316374421, 7823377.507483461871743 ] ], [ [ -2433906.987269800156355, 7858842.509372074157 ], [ -2359990.324205772485584, 7895939.639540608972311 ], [ -2285968.765630466397852, 7931271.657026222907007 ], [ -2211945.76174630690366, 7965472.228640222921968 ] ] ] } },
10 { "type": "Feature", "properties": { "transect_id": "T005", "vessel": "Bligh", "survey_date": "2025-08-19T00:00:00", "crosses_antimeridian_flag": true, "length_m": 337273.70270080183 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2730085.261179696302861, 7745776.327364278957248 ], [ -2661819.787075642962009, 7746489.832580281421542 ], [ -2593883.202560970094055, 7746760.809876747429371 ], [ -2526561.439846133813262, 7748375.548134338110685 ], [ -2459207.692624073475599, 7747464.851115341298282 ] ], [ [ -2392326.301384323276579, 7747142.532282743602991 ], [ -2325963.332817469257861, 7747812.099709572270513 ] ] ] } },
11 { "type": "Feature", "properties": { "transect_id": "T006", "vessel": "Cakaulevu", "survey_date": "2025-08-13T00:00:00", "crosses_antimeridian_flag": true, "length_m": 362346.84209049109 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2599992.844046104233712, 7710152.494721526280046 ], [ -2535990.336608688347042, 7745663.094245363026857 ], [ -2471907.25352796446532, 7780096.101796898059547 ] ], [ [ -2408021.86162570444867, 7815198.070424247533083 ], [ -2343992.843024157453328, 7848789.023065808229148 ], [ -2280128.756940491497517, 7882913.996305481530726 ], [ -2216075.889947677496821, 7915112.088575566187501 ] ] ] } },
12 { "type": "Feature", "properties": { "transect_id": "T007", "vessel": "Vanua I", "survey_date": "2025-08-19T00:00:00", "crosses_antimeridian_flag": true, "length_m": 368700.1434123707 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2707958.766985294874758, 7847662.46371332090348 ], [ -2617025.080956507474184, 7868560.6145184263587 ], [ -2526493.880338669288903, 7888512.674169298261404 ] ], [ [ -2436457.20139694865793, 7908226.102616477757692 ], [ -2346756.589748611208051, 7926750.916424177587032 ], [ -2257520.004844188690186, 7945076.104863223619759 ] ] ] } },
13 { "type": "Feature", "properties": { "transect_id": "T008", "vessel": "Taveuni II", "survey_date": "2025-08-12T00:00:00", "crosses_antimeridian_flag": true, "length_m": 130059.3914311858 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2518182.288068630266935, 7779851.174654245376587 ], [ -2487017.445418053306639, 7789178.679573908448219 ], [ -2456022.297383859753609, 7799241.849767371080816 ] ], [ [ -2425166.019995934329927, 7809880.026913052424788 ], [ -2394257.700750786811113, 7819872.499677928164601 ], [ -2363415.248306552879512, 7829983.100506925024092 ] ] ] } },
14 { "type": "Feature", "properties": { "transect_id": "T009", "vessel": "Vanua I", "survey_date": "2025-08-13T00:00:00", "crosses_antimeridian_flag": true, "length_m": 235691.09624016393 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2700142.167306652758271, 7911204.870228514075279 ], [ -2640985.695807782001793, 7916482.104912839829922 ], [ -2582072.975177893880755, 7921554.017558207735419 ], [ -2523489.242259116843343, 7927027.587514635175467 ] ], [ [ -2465150.952466951683164, 7932409.003623221069574 ], [ -2407078.076770230196416, 7937881.784215446561575 ] ] ] } },
15 { "type": "Feature", "properties": { "transect_id": "T010", "vessel": "Vanua I", "survey_date": "2025-08-15T00:00:00", "crosses_antimeridian_flag": true, "length_m": 362782.57626249455 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2743004.244949294254184, 7825703.487932769581676 ], [ -2559206.512722389306873, 7831590.124320032075047 ] ], [ [ -2377995.683071207255125, 7836498.912986122071743 ], [ -2199142.433008900843561, 7840154.290191553533077 ] ] ] } },
16 { "type": "Feature", "properties": { "transect_id": "T011", "vessel": "Taveuni II", "survey_date": "2025-08-20T00:00:00", "crosses_antimeridian_flag": false, "length_m": 85100.654515888978 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2090510.237545256037265, 7860563.718294717371464 ], [ -2104083.355092440266162, 7856360.095066314563155 ], [ -2117792.864098150283098, 7853092.239760281518102 ], [ -2131508.181665613316, 7849795.275641735643148 ], [ -2145064.558770742733032, 7845283.005933348089457 ], [ -2158751.349236745852977, 7841647.831423315219581 ], [ -2172374.122675319202244, 7837490.689390176907182 ] ] ] } },
17 { "type": "Feature", "properties": { "transect_id": "T012", "vessel": "Taveuni II", "survey_date": "2025-08-20T00:00:00", "crosses_antimeridian_flag": false, "length_m": 96678.572314157165 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2881358.679590006358922, 7711997.136072006076574 ], [ -2881147.548506676219404, 7744723.712745074182749 ], [ -2880792.575384852476418, 7777199.373172726482153 ], [ -2880163.700538771227002, 7808666.804016925394535 ] ] ] } },
18 { "type": "Feature", "properties": { "transect_id": "T013", "vessel": "Bligh", "survey_date": "2025-08-19T00:00:00", "crosses_antimeridian_flag": false, "length_m": 195242.20241007773 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2074347.516229145694524, 7874463.33793031796813 ], [ -2126661.583137985318899, 7835388.280761742964387 ], [ -2179084.771710069850087, 7797497.99072393681854 ], [ -2231266.005162506829947, 7758301.353639220818877 ] ] ] } },
19 { "type": "Feature", "properties": { "transect_id": "T014", "vessel": "Lomaiviti", "survey_date": "2025-08-13T00:00:00", "crosses_antimeridian_flag": false, "length_m": 168768.7882640101 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2884554.542054513935, 7889146.833948561921716 ], [ -2843184.396975137759, 7880624.016131930053234 ], [ -2802044.054834145121276, 7872489.953316772356629 ], [ -2760519.013364502228796, 7861046.430769282393157 ], [ -2719749.847674670163542, 7853185.46901720110327 ] ] ] } },
20 { "type": "Feature", "properties": { "transect_id": "T015", "vessel": "Vanua I", "survey_date": "2025-08-15T00:00:00", "crosses_antimeridian_flag": false, "length_m": 136075.16315041631 }, "geometry": { "type": "MultiLineString", "coordinates": [ [ [ -2154859.157849435694516, 7981607.483935452997684 ], [ -2176367.295431756414473, 7974281.162554035894573 ], [ -2198072.658420251682401, 7968293.111701854504645 ], [ -2219700.689059948083013, 7961552.54660858400166 ], [ -2241249.826771907042712, 7954069.077079316601157 ], [ -2262853.85095702810213, 7946839.612698352895677 ], [ -2284666.763064748141915, 7940965.200932309031487 ] ] ] } },
<system-reminder>Showed lines 1-20 of 37. Re-call Read with offset=21 to continue, or raise limit.</system-reminder>
0:29
Bash
ls -F
fiji_transects_fmg.geojson fiji_transects_wgs84.geojson solve.py
0:38