Hi,
I was just testing the approach with ogrinfo (GDAL 3.11.0dev) but maybe I am
doing something wrong.
This works in SpatiaLite gui (or at least the length is not the same):
Cartesian length
select ST_Length
(ST_GeomFromText
('LINESTRING ( 339775 6936992, 548057 6951815 )',3067));
208808.794961
Length along ellipsoid (accepts only Long/Lat coordinates, see
https://www.gaia-gis.it/gaia-sins/spatialite-sql-5.1.0.html:
select ST_Length
(ST_Transform(
ST_GeomFromText
('LINESTRING ( 339775 6936992, 548057 6951815 )',3067),4326)
,1);
208875.050186
Now the same with ogrinfo. I simplified the SQL by saving the test linesting
into a file in EPSG:3067.
ogrinfo -dialect sqlite -sql "select ST_Length(geometry) from length"
length.json
208808.794960845
Good so far. But with "use_ellipsoid" gives very unexpected result:
ogrinfo -dialect sqlite -sql "select ST_Length(geometry,1) from length"
length.json
417750.100376289
Same wrong result also with this:
ogrinfo -dialect sqlite -sql "select ST_Length(ST_Transform(geometry,4326),1)
from length" length.json
length.json is this:
{
"type": "FeatureCollection",
"crs": {"type": "name", "properties": { "name": "EPSG:3067" }},
"features": [
{ "type": "Feature", "properties": null, "geometry":
{"type":"LineString","coordinates":[[339775,6936992],[548057,6951815]]} }
]
}
-Jukka Rahkonen-
Lähettäjä: gdal-dev <[email protected]> Puolesta Even Rouault
via gdal-dev
Lähetetty: tiistai 21. tammikuuta 2025 12.45
Vastaanottaja: Thomas Knudsen <[email protected]>; Peter Bennewitz
<[email protected]>
Kopio: [email protected]
Aihe: Re: [gdal-dev] UTM local correction for height and
distance-to-reference-meridian ?
Le 21/01/2025 à 11:37, Thomas Knudsen via gdal-dev a écrit :
If you plan to transform to a different system anyway, I would definitely
prefer going to geographical coordinates, and computing the length of the
geodesic between the two points.
actually no need to do the explicit conversion to geographical coordinates, if
the appropriate SRS is attached to your geometry,
OGRGeometry::get_GeodesicLength() will do the right thing:
https://gdal.org/en/stable/api/ogrgeometry_cpp.html#_CPPv4NK13OGRLineString18get_GeodesicLengthEPK19OGRSpatialReference
Python API:
https://gdal.org/en/stable/api/python/vector_api.html#osgeo.ogr.Geometry.GeodesicLength
Python examples:
https://github.com/OSGeo/gdal/blob/master/autotest/ogr/ogr_geom.py#L4560
--
http://www.spatialys.com<http://www.spatialys.com/>
My software is free, but my time generally not.
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