[gdal-dev] gdaltranslate and gdalwarp rotating and resizing image without being asked to, why?

[Jesse McGraw]

Gdal gurus,

I'm writing a utility to automatically georeference Instrument Approach
Procedures and Airport Diagrams from the FAA (github.com/jlmcgraw, if
you're curious) and I'm hoping for some insight from the experts here as to
why I'm seeing the following behavior with Airport Diagrams

Most of the Airport Diagrams diagrams are portrait orientation (True North
up), however some of them are actually laid out in landscape orientation
(True North to the left or right) though the source PDF is still in portrait

If I georeference these landscape oriented using GCPs then gdalwarp will
swap X and Y axes and also resize the resulting bitmap (it also resizes
portrait oriented ones too, though without swapping axes)

My questions:
1) Why is gdalwarp swapping the axes rather than using the X and Y
pixel-skew parameters of the affine transformation (seems to be always 0)?
2) Why is it re-sizing the bitmap?
3) Do I have to do both of these steps separately (translate and then warp)
or can I simplify somehow?

Steps in the process:

1) Generate a list of Ground Control Points from the PDF, rasterize the PDF
to a 300dpi PNG

2) gdal_translate .PNG to an intermediate .VRT
("gdal_translate -q -of VRT -strict -a_srs EPSG:4326 $gcpstring
'$targetpng'  '$targetvrt'")

3) gdalwarp intermediate .VRT to get the final georeferenced output .VRT
 ("gdalwarp -q -of VRT -t_srs EPSG:4326 -order 1 -overwrite ''$targetvrt''
'$targetvrt2'")




*example from a landscape diagram*

(snippet of step 2 output from gdal_translate'd .vrt)
CA-SFO-00375AD-PDF-AIRPORT-DIAGRAM.vrt:
*<VRTDataset rasterXSize="1613" rasterYSize="2475">*

(snippet of step 3 output from gdalwarp'd .vrt)
warpedCA-SFO-00375AD.PDF-AIRPORT\ DIAGRAM.vrt:
*<VRTDataset rasterXSize="2623" rasterYSize="1359"
subClass="VRTWarpedDataset">*
*<GeoTransform> -1.2242081739746585e+02,  2.9114844968978991e-05,
0.0000000000000000e+00,  3.7641622693302779e+01,  0.0000000000000000e+00,
-2.9114844968978991e-05</GeoTransform>*


*example from a portrait diagram*
          (snippet of step 2 output from gdal_translate'd .vrt)
*VA-RIC-00347AD-PDF-AIRPORT-*
*DIAGRAM.vrt*
*<VRTDataset rasterXSize="1613" rasterYSize="2475">*

(snippet of step 3 output from gdalwarp'd .vrt)
*warpedVA-RIC-00347AD.PDF-*
*AIRPORT\ DIAGRAM.vrt*



*<VRTDataset rasterXSize="1870" rasterYSize="2287"
subClass="VRTWarpedDataset"><GeoTransform> -7.7341103107298423e+01,
2.1580033523515700e-05,  0.0000000000000000e+00,  3.7529840835409082e+01,
0.0000000000000000e+00, -2.1580033523515700e-05</GeoTransform>*
Thanks!
-Jesse McGraw
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20140627/6f660b8e/attachment-0001.html>