GDAL crop ECW file with coordinates

Question

I am looking to crop an ECW image based on latitude and longitude. I have the following code to do that but it doesn't work.

<gdalwarp -t_srs EPSG:27700 -te 51.50386 51.50391 -0.4333941 -0.4333865 image.ecw imagecrop.tif>

I get the following error.

Warning 1: -ts values have minx >= maxx. This will result in a horizontally flip ped image. Warning 1: -ts values have miny >= maxy. This will result in a vertically flippe d image. Creating output file that is -1297P x -1297L. ERROR 1: Attempt to create -1297x-1297 dataset is illegal,sizes must be larger t han zero.

How can I fix this?

Answer 1

Read https://www.gdal.org/gdalwarp.html carefully

-te xmin ymin xmax ymax:

set georeferenced extents of output file to be created (in target SRS by default, or in the SRS specified with -te_srs)

What is wrong that you have given xmin=51.50386 and xmax=-0.4333941. This should work better

-te 51.50386 -0.4333941 51.50391 -0.4333865

However, if you are close to London you have the coordinates in wrong order. GDAL wants them always as longitude-latitude or easting-northing order so the parameter would come

-te -0.4333941 51.50386 -0.4333865 51.50391

But then you should re-read the manual https://www.gdal.org/gdalwarp.html "(in target SRS by default, or in the SRS specified with -te_srs)". Your target is EPSG:27700 so either you must give the extents according to that or if you want to select the area by lon-lat coordinates you must tell that by adding the -te_srs parameter

-te_srs srs_def:

(GDAL >= 2.0) Specifies the SRS in which to interpret the coordinates given with -te. The srs_def may be any of the usual GDAL/OGR forms, complete WKT, PROJ.4, EPSG:n or a file containing the WKT. This must not be confused with -t_srs which is the target SRS of the output dataset. -te_srs is a convenience e.g. when knowing the output coordinates in a geodetic long/lat SRS, but still wanting a result in a projected coordinate system.

Add -te_srs epsg:4326 and it should finally work.