[gdal-dev] conversion of imagery which has an empty coordinate system to geotif format via gdalwarp

[John Mitchell]

Hi,

I would like to convert imagery which has an empty coordinate system to
geotif format via gdalwarp:

Below is part of a gdalinfo dump of the original imagery.  Notice that the
Coordinate System is empty
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Size is 12074, 13232
Coordinate System is `'
GCP Projection = GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,
298.257223563
,AUTHORITY["EPSG",7030]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY["EPSG",6326]],PRIMEM["Greenwich",0,AUTHORITY["EPSG",8901]],UNIT["DMSH",
0.0174532925199433
,AUTHORITY["EPSG",9108]],AXIS["Lat",NORTH],AXIS["Long",EAST],AUTHORITY["EPSG",4326]]
GCP[  0]: Id=1, Info=
          (0.5,0.5) -> (36.77378,-17.270641,0)
GCP[  1]: Id=2, Info=
          (6037,0.5) -> (35.398528,-16.938865,0)
GCP[  2]: Id=3, Info=
          (12073.5,0.5) -> (34.027899,-16.597882,0)
GCP[  3]: Id=4, Info=
          (0.5,3307.5) -> (36.58987,-17.99724,0)
GCP[  4]: Id=5, Info=
          (6037,3307.5) -> (35.209644,-17.663643,0)
GCP[  5]: Id=6, Info=
          (12073.5,3307.5) -> (33.834311,-17.320427,0)
GCP[  6]: Id=7, Info=
          (0.5,6614.5) -> (36.404318,-18.723611,0)
GCP[  7]: Id=8, Info=
          (6037,6614.5) -> (35.01887,-18.388159,0)
GCP[  8]: Id=9, Info=
          (12073.5,6614.5) -> (33.638591,-18.042675,0)
GCP[  9]: Id=10, Info=
          (0.5,9921.5) -> (36.21706,-19.449749,0)
GCP[ 10]: Id=11, Info=
          (6037,9921.5) -> (34.826137,-19.112408,0)
GCP[ 11]: Id=12, Info=
          (12073.5,9921.5) -> (33.440671,-18.764619,0)
GCP[ 12]: Id=13, Info=
          (0.5,13228.5) -> (36.028031,-20.175626,0)
GCP[ 13]: Id=14, Info=
          (6037,13228.5) -> (34.631381,-19.836361,0)
GCP[ 14]: Id=15, Info=
          (12073.5,13228.5) -> (33.24048,-19.486228,0)
Metadata:
  ELLIPSOID=WGS84
Corner Coordinates:
Upper Left  (    0.0,    0.0)
Lower Left  (    0.0,13232.0)
Upper Right (12074.0,    0.0)
Lower Right (12074.0,13232.0)
Center      ( 6037.0, 6616.0)
Band 1 Block=12074x1 Type=Byte, ColorInterp=Undefined
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


Based on the above gdalinfo data I assumed that the projection should be
wgs84/EPSG:4326

So I run the following command against the imagery to convert it to geotiff
with an EPSG code of 4326:
gdalwarp -rc -s_srs epsg:4326 -t_srs epsg:4326 source_imagery
destination_geotiff

Next I run gdalinfo against the converted geotiff file which is listed
below:
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Driver: GTiff/GeoTIFF
Files: C:\dat_01.tif
Size is 15174, 15369
Coordinate System is:
GEOGCS["WGS 84",
    DATUM["WGS_1984",
        SPHEROID["WGS 84",6378137,298.2572235630016,
            AUTHORITY["EPSG","7030"]],
        AUTHORITY["EPSG","6326"]],
    PRIMEM["Greenwich",0],
    UNIT["degree",0.0174532925199433],
    AUTHORITY["EPSG","4326"]]
Origin = (33.240318507099211,-16.597638311748319)
Pixel Size = (0.000232863689106,-0.000232863689106)
Metadata:
  AREA_OR_POINT=Area
Image Structure Metadata:
  INTERLEAVE=BAND
Corner Coordinates:
Upper Left  (  33.2403185, -16.5976383) ( 33d14'25.15"E, 16d35'51.50"S)
Lower Left  (  33.2403185, -20.1765203) ( 33d14'25.15"E, 20d10'35.47"S)
Upper Right (  36.7737921, -16.5976383) ( 36d46'25.65"E, 16d35'51.50"S)
Lower Right (  36.7737921, -20.1765203) ( 36d46'25.65"E, 20d10'35.47"S)
Center      (  35.0070553, -18.3870793) ( 35d 0'25.40"E, 18d23'13.49"S)
Band 1 Block=15174x1 Type=Byte, ColorInterp=Gray
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

The readme file has the CORNER COORDINATES of:
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

       17°16'14.30" S      16°35'52.37" S
       36°46'25.60" E      34°01'40.43" E

       20°10'34.62" S      19°29'12.77" S
       36°01'40.29" E      33°14'25.06" E

CENTER       18°22'S   035°01'E
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

In comparing the readme file to converted geotiff the resolution increased
slightly and the coordinates were slightly different.
Am I correct in assuming that the EPSG code should be 4326 when converting
to geotiff format via gdalwarp?

Thanks,

John J. Mitchell
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/gdal-dev/attachments/20080226/f5f92895/attachment-0001.html