Even, Thank you for the very detailed responses. Time to go do some more googling on GDAL perl bindings (or dig into python)
On Tue, Jul 1, 2014 at 4:37 PM, Even Rouault <even.roua...@mines-paris.org> wrote: > Le mardi 01 juillet 2014 15:50:18, Jesse McGraw a écrit : > > On Mon, Jun 30, 2014 at 3:07 PM, Even Rouault > > <even.roua...@mines-paris.org> > > > > wrote: > > > That might the problem. If you create the GCPs on the PDF and not on > the > > > PNG, > > > and that the PDF has rotation, pdftoppm I think will apply the > rotation, > > > hence > > > the axis swapping. > > > > Remember, I'm using the PNG I've created for all gdal operations, gdal > > never interacts with the source PDF > > > > I'm probably fundamentally misunderstanding some aspect of the command > > lines I'm using in gdal*. My end goal is to get the necessary affine > > transformation information to display the PNG I create in step 3a > properly > > in a separate Android moving-map application (eg. your current position > > displayed on the diagram as you move around the airport) > > Jesse, > > hum ok, with the images I think I now understand the situation (I've only > looked at the landscape diagram) and what you want. > > You probably don't want to use gdalwarp, which by default will result in a > north-up image. You likely want to compute the geotransform affine matrix > for > your GCPs and set it, since indeed your GCPs define a 1st-order > transformation. > > The GDAL C API has GDALGCPsToGeoTransform() which does exactly this. I see > it > is also available in the Python API : gdal.GCPsToGeoTransform(). > See http://svn.osgeo.org/gdal/trunk/autotest/gcore/gcps2geotransform.py > for > how to use it. > > You could then just do a CreateCopy() of the PNG to a VRT, and set the > returned geotransform by the previous step with SetGeoTransform(). > > Even > > > -- > Geospatial professional services > http://even.rouault.free.fr/services.html >
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