[gdal-dev] Where is the projection info stored in a GDAL dataset?

[Joaquim Manuel Freire Luís]

Hi,

I am trying to use the GDAL shared lib directly from Julia and there are things that keep breaking my head. For example, the lines below use a mix of GMT and GDAL wrapper functions calls that WORK. First command creates a GMT dataset with two UTM points type with an assigned coordinate system. Next, in 2), I create a GDAL dataset of a LineString, convert it to geog in 3) and save it to file using the OGR_GMT driver in 4)

1) D2 = mat2ds([588977.324434907 4095339.69117669; 579551.921920776 4150721.71333039], proj="+proj=utm +zone=29");
2) ds = gmt2gd(D2);
3) ds2=ogr2ogr(ds, ["-t_srs", "+proj=longlat", "-overwrite"])
4) ogr2ogr(ds2, dest="lixo2.gmt")

Now the troubles. When I tried to use GDALSetProjection() I got an error like this

ERROR 6: /vsimem/##269: Dataset does not support the SetSpatialRef() method.

So I found that I could set the CRS with GDALDatasetCreateLayer() while creating a layer on the dataset (using the Memory driver)
(https://github.com/GenericMappingTools/GMT.jl/blob/master/src/gdal_utils.jl#L254)

But oddly trying to inquiry the *ds* with GDALGetSpatialRef() returns an empty pointer. I.e.:

julia> Gdal.GDALGetSpatialRef(ds.ptr)
Ptr{Nothing} @0x0000000000000000

However the CSR was well sored in some place because the ="lixo2.gmt" is correct (it has this)

# @VGMT1.0 @GLINESTRING
# @R-8.1/-8/37/37.5
# @Jp"+proj=longlat +datum=WGS84 +no_defs"
# @Jw"GEOGCS[\"unknown\",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\"]],AXIS[\"Longitude\",EAST],AXIS[\"Latitude\",NORTH]]"
# FEATURE_DATA
>
-8 37.0
-8.1 37.5

But my trouble is that I want to fish the CRS from the ogr2ogr dataset (the ds2 above) so that I can convert back from GDAL to GMT (which I already can) without having to save to a file in disk.

So basically my question is where is that CRS stored and how can I access it?

Thanks

Joaquim
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