[GRASS-user] Datum not recognized by Grass
Markus Metz
markus.metz.giswork at gmail.com
Tue Dec 10 12:36:06 PST 2019
Within GRASS:
g.proj epsg=2932 -p
-PROJ_INFO-------------------------------------------------
name : QND95 / Qatar National Grid
ellps : international
proj : tmerc
lat_0 : 24.45
lon_0 : 51.2166666666667
k : 0.99999
x_0 : 200000
y_0 : 300000
towgs84 :
-119.4248,-303.65872,-11.00061,1.164298,0.174458,1.096259,3.657065
no_defs : defined
-PROJ_EPSG-------------------------------------------------
epsg : 2932
-PROJ_UNITS------------------------------------------------
unit : meter
units : meters
meters : 1
looks fine.
Outside GRASS, using projinfo from PROJ 6.2.1:
projinfo -o PROJ -s EPSG:2932 -t EPSG:4326
Candidate operations found: 1
-------------------------------------
Operation n°1:
unknown id, Inverse of Qatar National Grid + QND95 to WGS 84 (1), 0 m,
Qatar - onshore
PROJ string:
+proj=pipeline
+step +inv +proj=tmerc +lat_0=24.45 +lon_0=51.2166666666667 +k=0.99999
+x_0=200000 +y_0=300000 +ellps=intl
+step +proj=push +v_3 +step +proj=cart +ellps=intl
+step +proj=helmert +x=-119.4248 +y=-303.65872 +z=-11.00061 +rx=1.164298
+ry=0.174458 +rz=1.096259 +s=3.657065 +convention=position_vector
+step +inv +proj=cart +ellps=WGS84 +step +proj=pop +v_3
+step +proj=unitconvert +xy_in=rad +xy_out=deg +step
+proj=axisswap +order=2,1
Datum transformation happens with +proj=helmert which is the same as the
towgs84 parameters in GRASS. This does not matter, GRASS does not use these
parameters for reprojection, it relies on PROJ to select an appropriate
datum transformation depending on the source and target CRS.
Markus M
On Mon, Dec 9, 2019 at 10:15 PM Markus Metz <markus.metz.giswork at gmail.com>
wrote:
>
>
> On Wed, Dec 4, 2019 at 12:23 PM Zoltan Szecsei <zoltans at geograph.co.za>
> wrote:
> >
> > Hi Helmut,
> > Thanks for your comments.
> >
> > I installed everything with OSGeo4W64, and QGIS get the EPSG:2932 but
> > Grass not.
> >
> > Perhaps I have a PATH or some other setting problem?
> > Perhaps let me know what search paths Grass uses for proj4, and what
> > proj files and locations I should scan for.
>
> In this case where the EPSG code is known, there is no need to do anything
> but to ignore the warning. GRASS will use the EPSG code if available and
> passes it to PROJ when it comes to reprojection.
>
> Markus M
>
> >
> > Regards,
> > Zoltan
> >
> > On 2019/12/04 01:30, Helmut Kudrnovsky wrote:
> > >> ignore the warning and use GRASS with PROJ6, granted that authority
> name
> > > (e.g. EPSG) and authority code (e.g. 2932) are known for both CRS's in
> case
> > > of reprojection
> > >
> > > this issue is already by GRASS with PROJ6, see
> > >
> > > ####################
> > > GRASS version: 7.8.1
> > > Code revision: c865432c9
> > > Build date: 2019-11-10
> > > Build platform: x86_64-w64-mingw32
> > > GDAL: 3.0.2
> > > PROJ: 6.2.1 <=
> > > GEOS: 3.8.0
> > > SQLite: 3.29.0
> > > Python: 3.7.0
> > > wxPython: 4.0.7
> > > Platform: Windows-10-10.0.18362-SP0 (OSGeo4W)
> > > ####################
> > >
> > > and the output from the underlying PROJ: 6.2.1
> > >
> > > ####################
> > > C:\>projinfo EPSG:2932 -o PROJ,WKT2_2018
> > > PROJ.4 string:
> > > +proj=tmerc +lat_0=24.45 +lon_0=51.2166666666667 +k=0.99999 +x_0=200000
> > > +y_0=300000 +ellps=intl
> > >
> +towgs84=-119.4248,-303.65872,-11.00061,1.164298,0.174458,1.096259,3.657065
> > > +units=m +no_defs +type=crs
> > >
> > > WKT2_2018 string:
> > > PROJCRS["QND95 / Qatar National Grid",
> > > BASEGEOGCRS["QND95",
> > > DATUM["Qatar National Datum 1995",
> > > ELLIPSOID["International 1924",6378388,297,
> > > LENGTHUNIT["metre",1]]],
> > > PRIMEM["Greenwich",0,
> > > ANGLEUNIT["degree",0.0174532925199433]],
> > > ID["EPSG",4614]],
> > > CONVERSION["Qatar National Grid",
> > > METHOD["Transverse Mercator",
> > > ID["EPSG",9807]],
> > > PARAMETER["Latitude of natural origin",24.45,
> > > ANGLEUNIT["degree",0.0174532925199433],
> > > ID["EPSG",8801]],
> > > PARAMETER["Longitude of natural origin",51.2166666666667,
> > > ANGLEUNIT["degree",0.0174532925199433],
> > > ID["EPSG",8802]],
> > > PARAMETER["Scale factor at natural origin",0.99999,
> > > SCALEUNIT["unity",1],
> > > ID["EPSG",8805]],
> > > PARAMETER["False easting",200000,
> > > LENGTHUNIT["metre",1],
> > > ID["EPSG",8806]],
> > > PARAMETER["False northing",300000,
> > > LENGTHUNIT["metre",1],
> > > ID["EPSG",8807]]],
> > > CS[Cartesian,2],
> > > AXIS["(E)",east,
> > > ORDER[1],
> > > LENGTHUNIT["metre",1]],
> > > AXIS["(N)",north,
> > > ORDER[2],
> > > LENGTHUNIT["metre",1]],
> > > USAGE[
> > > SCOPE["unknown"],
> > > AREA["Qatar - onshore"],
> > > BBOX[24.55,50.69,26.2,51.68]],
> > > ID["EPSG",2932]]
> > > ####################
> > >
> > >> The problem is that GRASS still assumes datum transformation from X to
> > > WGS84, whereas with PROJ6,
> > >> WGS84 is no longer required as pivot datum. Datum transformations from
> > > datum X to datum Y can
> > >> sometimes (often) be done without going through WGS84. The
> requirement is
> > > to have EPSG or other
> > >> authority codes and to use PROJ 6.
> > > this warning is just from a simple v.in.ogr of a EPSG:2932-based
> shapefile
> > > into a EPSG:2932-created GRASS location.
> > >
> > > so, there may be some more adaptions needed for actions like v.in.ogr
> and
> > > co?
> > >
> > >
> > >
> > > -----
> > > best regards
> > > Helmut
> > > --
> > > Sent from:
> http://osgeo-org.1560.x6.nabble.com/Grass-Users-f3884509.html
> > > _______________________________________________
> > > grass-user mailing list
> > > grass-user at lists.osgeo.org
> > > https://lists.osgeo.org/mailman/listinfo/grass-user
> >
> > --
> >
> > =============================================
> > Zoltan Szecsei GPrGISc 0031
> > Geograph (Pty) Ltd.
> > GIS and Photogrammetric Services
> >
> > P.O. Box 7, Muizenberg 7950, South Africa.
> >
> > Mobile: +27-83-6004028 (WhatsApp only)
> > Qatar: +974 5083 2722 www.geograph.co.za
> > =============================================
> >
> > _______________________________________________
> > grass-user mailing list
> > grass-user at lists.osgeo.org
> > https://lists.osgeo.org/mailman/listinfo/grass-user
>
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