No proj4 definition for CH1903/LV03 (EPSG 21781) maps

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No proj4 definition for CH1903/LV03 (EPSG 21781) maps

Christian Aichinger
Hi,

I have maps with CH1903/LV03/EPSG 21781 coordinates. They worked fine
with previous versions of libgeotiff. The current libgeotiff can still
read them, but can't produce a proj4 definition for them. Unfortunately,
I needed that feature.

The problem seems to be the May 2012 Hotine rework[1]. EPSG 21781 now
gets mapped to CTProjection == CT_HotineObliqueMercatorAzimuthCenter,
but that is not supported in GTIFGetProj4Defn() in geotiff_proj4.c, only
CT_ObliqueMercator is.

I'm not sure how to best approach this problem. Should projop_wparam.csv
be modified so it gives CT_ObliqueMercator with the correct parameters?
Or should CT_HotineObliqueMercatorAzimuthCenter just be handled in
GTIFGetProj4Defn()?

I've attached a sample file that shows the problem. To reproduce, run
`listgeo -proj4 CH1903-sample.tif` and observe that no proj4 definition
is shown.

Cheers,
Chris

[1]: http://lists.maptools.org/pipermail/geotiff/2012-May/000720.html


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CH1903-sample.tif (1K) Download Attachment
listgeo.txt (966 bytes) Download Attachment
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Re: No proj4 definition for CH1903/LV03 (EPSG 21781) maps

Even Rouault-2
Le samedi 02 mai 2015 13:17:42, Christian Aichinger a écrit :

> Hi,
>
> I have maps with CH1903/LV03/EPSG 21781 coordinates. They worked fine
> with previous versions of libgeotiff. The current libgeotiff can still
> read them, but can't produce a proj4 definition for them. Unfortunately,
> I needed that feature.
>
> The problem seems to be the May 2012 Hotine rework[1]. EPSG 21781 now
> gets mapped to CTProjection == CT_HotineObliqueMercatorAzimuthCenter,
> but that is not supported in GTIFGetProj4Defn() in geotiff_proj4.c, only
> CT_ObliqueMercator is.
>
> I'm not sure how to best approach this problem. Should projop_wparam.csv
> be modified so it gives CT_ObliqueMercator with the correct parameters?
> Or should CT_HotineObliqueMercatorAzimuthCenter just be handled in
> GTIFGetProj4Defn()?
>
> I've attached a sample file that shows the problem. To reproduce, run
> `listgeo -proj4 CH1903-sample.tif` and observe that no proj4 definition
> is shown.

Christian,

I've just committed in libgeotiff trunk a fix for that (inspired from GDAL
similar code).

So now:

$ bin/listgeo -proj4 /tmp/CH1903-sample.tif
Geotiff_Information:
   Version: 1
   Key_Revision: 1.0
   Tagged_Information:
      ModelTiepointTag (2,3):
         0                 0                 0                
         620000            172000            0                
      ModelPixelScaleTag (1,3):
         2.5               2.5               0                
      End_Of_Tags.
   Keyed_Information:
      GTModelTypeGeoKey (Short,1): ModelTypeProjected
      GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
      ProjectedCSTypeGeoKey (Short,1): Unknown-21781
      ProjLinearUnitsGeoKey (Short,1): Linear_Meter
      End_Of_Keys.
   End_Of_Geotiff.

PCS = 21781 (CH1903 / LV03)
Projection = 19922 (Swiss Oblique Mercator 1903M)
Projection Method: CT_HotineObliqueMercatorAzimuthCenter
   ProjCenterLatGeoKey: 46.952406 ( 46d57' 8.66"N)
   ProjCenterLongGeoKey: 7.439583 (  7d26'22.50"E)
   ProjAzimuthAngleGeoKey: 90.000000 ( 90d 0' 0.00"N)
   ProjRectifiedGridAngleGeoKey: 90.000000 ( 90d 0' 0.00"N)
   ProjScaleAtCenterGeoKey: 1.000000
   ProjFalseEastingGeoKey: 600000.000000 m
   ProjFalseNorthingGeoKey: 200000.000000 m
GCS: 4149/CH1903
Datum: 6149/CH1903
Ellipsoid: 7004/Bessel 1841 (6377397.16,6356078.96)
Prime Meridian: 8901/Greenwich (0.000000/  0d 0' 0.00"E)
Projection Linear Units: 9001/metre (1.000000m)

PROJ.4 Definition: +proj=somerc +lat_0=46.95240555555556
+lon_0=7.439583333333333 +k_0=1 +x_0=600000 +y_0=200000 +a=6377397.155
+b=6356078.963 +units=m

Corner Coordinates:
Upper Left    (  620000.000,  172000.000)  (  7d42' 4.02"E, 46d42' 0.74"N)
Lower Left    (  620000.000,  171875.000)  (  7d42' 4.01"E, 46d41'56.69"N)
Upper Right   (  620125.000,  172000.000)  (  7d42' 9.91"E, 46d42' 0.73"N)
Lower Right   (  620125.000,  171875.000)  (  7d42' 9.89"E, 46d41'56.68"N)
Center        (  620062.500,  171937.500)  (  7d42' 6.96"E, 46d41'58.71"N)

Even


>
> Cheers,
> Chris
>
> [1]: http://lists.maptools.org/pipermail/geotiff/2012-May/000720.html

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