[gdal-dev] GetGeoTransform() valid?

[Wim de Vries]

On 04/24/2013 09:26 AM, Frank Warmerdam wrote:
>
> On Wed, Apr 24, 2013 at 12:21 AM, Wim de Vries <wsvries at xs4all.nl 
> <mailto:wsvries at xs4all.nl>> wrote:
>
>     Thanks for taking the time to answer.
>     On 04/24/2013 02:07 AM, Frank Warmerdam wrote:
>     ...
>
>>     Is the relationship between your images and geographic (lat/long)
>>     coordinate space affine?  If so, a geotransform will do just
>>     fine.  (ie. is the pixel spacing uniform over the image in terms
>>     of decimal degrees)
>     If I understand you correctly, it cannot be used for e.g. a
>     lambert conformal > cartesian (eg. bitmap x,y pixels), because
>     lons are not parallel and lats are bend when being projected.
>
>
>
> Well, it can potentially be but that is a more complicated case.  You 
> need to also provide a proper definition of the lambert conformal 
> coordinate system, and then the affine transformation from pixel/line 
> coordinates to meter coordinates in that projected coordinate system.
>
> For instance, another projected example is seen in this file.  The 
> coordiante system is transverse mercator with particular parameters 
> and the geotransform relates to the origin and pixel size given below. 
>  Given this information GDAL knows how to relate pixels to lat/long as 
> you can see in the corners reported.
Thanks.
I did use PROJ4, but with GDAL I can simply read-in geotiffs (these give 
info as you indicate below).
So, I can use getGeoTransform as long as the info (as below) is available.
Only thing to do is getting from meters to pixels (60mtr/pix in the 
example below for both x,y) and vice versa,
cartesian 0,0 being at 0lon 0lat?


>
> Size is 512, 512
> Coordinate System is:
> PROJCS["NAD27 / UTM zone 11N",
>     GEOGCS["NAD27",
>         DATUM["North_American_Datum_1927",
>             SPHEROID["Clarke 1866",6378206.4,294.9786982139006,
>                 AUTHORITY["EPSG","7008"]],
>             AUTHORITY["EPSG","6267"]],
>         PRIMEM["Greenwich",0],
>         UNIT["degree",0.0174532925199433],
>         AUTHORITY["EPSG","4267"]],
>     PROJECTION["Transverse_Mercator"],
>     PARAMETER["latitude_of_origin",0],
>     PARAMETER["central_meridian",-117],
>     PARAMETER["scale_factor",0.9996],
>     PARAMETER["false_easting",500000],
>     PARAMETER["false_northing",0],
>     UNIT["metre",1,
>         AUTHORITY["EPSG","9001"]],
>     AUTHORITY["EPSG","26711"]]
> Origin = (440720.000000000000000,3751320.000000000000000)
> Pixel Size = (60.000000000000000,-60.000000000000000)
> Metadata:
>   AREA_OR_POINT=Area
> Image Structure Metadata:
>   INTERLEAVE=BAND
> Corner Coordinates:
> Upper Left  (  440720.000, 3751320.000) (117d38'28.21"W, 33d54' 8.47"N)
> Lower Left  (  440720.000, 3720600.000) (117d38'20.79"W, 33d37'31.04"N)
> Upper Right (  471440.000, 3751320.000) (117d18'32.07"W, 33d54'13.08"N)
> Lower Right (  471440.000, 3720600.000) (117d18'28.50"W, 33d37'35.61"N)
> Center      (  456080.000, 3735960.000) (117d28'27.39"W, 33d45'52.46"N)
> Band 1 Block=512x16 Type=Byte, ColorInterp=Gray
>
> Best regards,
>
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, 
> warmerdam at pobox.com <mailto:warmerdam at pobox.com>
> light and sound - activate the windows | http://pobox.com/~warmerdam 
> <http://pobox.com/%7Ewarmerdam>
> and watch the world go round - Rush    | Geospatial Software Developer

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