[GRASS-dev] [GRASS GIS] #2893: Specify crs when exporting to GeoJSON

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1

#2893: Specify crs when exporting to GeoJSON
-------------------------+-------------------------
Reporter: pmav99 | Owner: grass-dev@…
     Type: defect | Status: new
Priority: normal | Milestone:
Component: Default | Version: unspecified
Keywords: v.out.ogr | CPU: Unspecified
Platform: Unspecified |
-------------------------+-------------------------
If the information is available, `v.out.ogr` should probably specify the
"crs" attribute when exporting to GeoJSON. `ogr2ogr` seems to support this
feature.

{{{
$ pacman -Qs gdal
local/gdal 2.0.1-6
     A translator library for raster geospatial data formats
}}}

A `GeoJSON` file with no `crs`:
{{{
$ cat sample.json
{
     "type": "Polygon",
     "coordinates": [
         [
             [ -84.32281494140625, 34.9895035675793 ],
             [ -84.29122924804688, 35.21981940793435 ],
             [ -84.24041748046875, 35.25459097465022 ],
             [ -84.32281494140625, 34.9895035675793 ]
         ]
     ]
}
}}}

Reprojecting:
{{{
$ ogr2ogr -f GeoJSON -t_srs "EPSG:3857" 3857.json sample.json

$ ogr2ogr -f GeoJSON -t_srs "EPSG:4326" 4326.json sample.json
}}}

The new files:
{{{
$ cat 3857.json
{
"type": "FeatureCollection",
"crs": { "type": "name", "properties": { "name":
"urn:ogc:def:crs:EPSG::3857" } },

"features": [
{ "type": "Feature", "properties": { }, "geometry": { "type": "Polygon",
"coordinates": [ [ [ -9386772.821532785892487, 4162454.812297557480633 ],
[ -9383256.718231666833162, 4193793.993894479703158 ], [
-9377600.378138564527035, 4198533.089648159220815 ], [
-9386772.821532785892487, 4162454.812297557480633 ] ] ] } }
]
}
}}}

{{{
$ cat 4326.json
{
"type": "FeatureCollection",
"crs": { "type": "name", "properties": { "name":
"urn:ogc:def:crs:OGC:1.3:CRS84" } },

"features": [
{ "type": "Feature", "properties": { }, "geometry": { "type": "Polygon",
"coordinates": [ [ [ -84.32281494140625, 34.989503567579298 ], [
-84.291229248046875, 35.219819407934352 ], [ -84.24041748046875,
35.25459097465022 ], [ -84.32281494140625, 34.989503567579298 ] ] ] } }
]
}
}}}

By the way, when crs is not defined `ogrinfo` seems to default to
`EPSG:4326` which I guess is the most reasonable choice, although I think
I would prefer something more explicit (e.g. a warning):
{{{
$ ogrinfo -so -al sample.json

ERROR 4: GeoJSON Driver doesn't support update.
Had to open data source read-only.
INFO: Open of `sample.json'
       using driver `GeoJSON' successful.
Layer name: OGRGeoJSON
Geometry: Polygon
Feature Count: 1
Extent: (-84.322815, 34.989504) - (-84.240417, 35.254591)
Layer SRS WKT:
GEOGCS["WGS 84",
     DATUM["WGS_1984",
         SPHEROID["WGS 84",6378137,298.257223563,
             AUTHORITY["EPSG","7030"]],
         AUTHORITY["EPSG","6326"]],
     PRIMEM["Greenwich",0,
         AUTHORITY["EPSG","8901"]],
     UNIT["degree",0.0174532925199433,
         AUTHORITY["EPSG","9122"]],
     AUTHORITY["EPSG","4326"]]
}}}

--
Ticket URL: <https://trac.osgeo.org/grass/ticket/2893&gt;
GRASS GIS <https://grass.osgeo.org>

2

#2893: Specify crs when exporting to GeoJSON
--------------------------+-------------------------
  Reporter: pmav99 | Owner: grass-dev@…
      Type: defect | Status: new
  Priority: normal | Milestone:
Component: Default | Version: unspecified
Resolution: | Keywords: v.out.ogr
       CPU: Unspecified | Platform: Unspecified
--------------------------+-------------------------

Comment (by pmav99):

Hmm... it seems `ogr2ogr`'s implicit choices can lead to bugs :

If we erase the CRS field from `3857.json`:
{{{
$ cat 3857.json
{
"type": "FeatureCollection",
"features": [
{ "type": "Feature", "properties": { }, "geometry": { "type": "Polygon",
"coordinates": [ [ [ -9386772.821532785892487, 4162454.812297557480633 ],
[ -9383256.718231666833162, 4193793.993894479703158 ], [
-9377600.378138564527035, 4198533.089648159220815 ], [
-9386772.821532785892487, 4162454.812297557480633 ] ] ] } }
]
}
}}}
Then `ogrinfo` assumes that EPSG is 4326:
{{{
$ ogrinfo -so -al 3857.json
ERROR 4: GeoJSON Driver doesn't support update.
Had to open data source read-only.
INFO: Open of `3857.json'
       using driver `GeoJSON' successful.

Layer name: OGRGeoJSON
Geometry: Polygon
Feature Count: 1
Extent: (-9386772.821533, 4162454.812298) - (-9377600.378139,
4198533.089648)
Layer SRS WKT:
GEOGCS["WGS 84",
     DATUM["WGS_1984",
         SPHEROID["WGS 84",6378137,298.257223563,
             AUTHORITY["EPSG","7030"]],
         AUTHORITY["EPSG","6326"]],
     PRIMEM["Greenwich",0,
         AUTHORITY["EPSG","8901"]],
     UNIT["degree",0.0174532925199433,
         AUTHORITY["EPSG","9122"]],
     AUTHORITY["EPSG","4326"]]
}}}
reprojecting does not make any changes to the coords (which is reasonable
I guess):
{{{
$ ogr2ogr -f GeoJSON -t_srs "EPSG:4326" 4326_implicit.json 3857.json

$ cat 4326_implicit.json
{
"type": "FeatureCollection",
"crs": { "type": "name", "properties": { "name":
"urn:ogc:def:crs:OGC:1.3:CRS84" } },
"features": [
{ "type": "Feature", "properties": { }, "geometry": { "type": "Polygon",
"coordinates": [ [ [ -9386772.821532784029841, 4162454.812297557014972 ],
[ -9383256.718231666833162, 4193793.993894479703158 ], [
-9377600.378138564527035, 4198533.089648158289492 ], [
-9386772.821532784029841, 4162454.812297557014972 ] ] ] } }
]
}
}}}
but this particular `(coords, crs)` combination is obviously garbage:
{{{
$ ogr2ogr -f GeoJSON -t_srs "EPSG:3857" 3857_implicit.json
4326_implicit.json

Failed to reproject feature 0 (geometry probably out of source or
destination SRS).
ERROR 1: Terminating translation prematurely after failed
translation of layer OGRGeoJSON (use -skipfailures to skip errors)
}}}

--
Ticket URL: <https://trac.osgeo.org/grass/ticket/2893#comment:1&gt;
GRASS GIS <https://grass.osgeo.org>

3

#2893: Specify crs when exporting to GeoJSON
--------------------------+-------------------------
  Reporter: pmav99 | Owner: grass-dev@…
      Type: defect | Status: new
  Priority: normal | Milestone:
Component: Default | Version: unspecified
Resolution: | Keywords: v.out.ogr
       CPU: Unspecified | Platform: Unspecified
--------------------------+-------------------------

Comment (by rouault):

Quoting the geojson spec ( http://geojson.org/geojson-spec.html
#coordinate-reference-system-objects ) : "The default CRS is a geographic
coordinate reference system, using the WGS84 datum, and with longitude and
latitude units of decimal degrees." . So OGR behaviour follows the spec.

And the new geojson spec ( https://www.ietf.org/id/draft-ietf-
geojson-00.txt ) deprecates the use of other CRS : "Other coordinate
reference systems, including ones described by CRS objects of the kind
defined in [GJ2008] are NOT RECOMMENDED"

--
Ticket URL: <http://trac.osgeo.org/grass/ticket/2893#comment:2&gt;
GRASS GIS <https://grass.osgeo.org>

4

#2893: Specify crs when exporting to GeoJSON
--------------------------+-------------------------
  Reporter: pmav99 | Owner: grass-dev@…
      Type: defect | Status: new
  Priority: normal | Milestone: 7.0.5
Component: Default | Version: unspecified
Resolution: | Keywords: v.out.ogr
       CPU: Unspecified | Platform: Unspecified
--------------------------+-------------------------
Changes (by nikosa):

* milestone: => 7.0.5

Comment:

If I understand correctly, this ticket can be closed?

--
Ticket URL: <https://trac.osgeo.org/grass/ticket/2893#comment:3&gt;
GRASS GIS <https://grass.osgeo.org>

5

#2893: Specify crs when exporting to GeoJSON
--------------------------+-------------------------
  Reporter: pmav99 | Owner: grass-dev@…
      Type: defect | Status: closed
  Priority: normal | Milestone: 7.0.5
Component: Default | Version: unspecified
Resolution: invalid | Keywords: v.out.ogr
       CPU: Unspecified | Platform: Unspecified
--------------------------+-------------------------
Changes (by neteler):

* status: new => closed
* resolution: => invalid

Comment:

It seems that the specs are respected, so not much we can do here.
Closing.

--
Ticket URL: <https://trac.osgeo.org/grass/ticket/2893#comment:4&gt;
GRASS GIS <https://grass.osgeo.org>