SOURCE_EXTRA default value of GDALWarpOptions too small

[mchapman]

Please see the attached sub-region screen capture of an image I created using gdalwarp 1.9. I used MS Paint to highlight in red several columns of pixels that repeat a pattern from left to right across the image (vertically only) where the pixels are the same color for both pixel columns when in fact they should be different. The problem seems to occur whether I am going from source wkt (wgs84 in this case) to the same coord system or if I go from wgs84 to another coord system. It only seems to happen when the source image is in WGS84 though. The problem seems to be with the default SOURCE_EXTRA parameter of the GDALWarpOptions being defaulted to 1. When I up that number everything works fine. I think the default for that value should be larger because it is hard to identify that this problem has occurred unless you do a detailed analysis of the pixels so an end user may screw up their data unknowningly. In order to reproduce the error you can send me an email and I will upload the image I used to identify the problem. The image is about 80MB so I will need an ftp site to put it on. To re-create the issue with gdalwarp simply warp the image to a copy of itself or specify a sub-region using the same WGS84 SRS or convert it to UTM.

[mchapman]

gdalwarp

[Jukka Rahkonen]

I believe that we would need more evidence before changing the default value of SOURCE_EXTRA. The current default seems to work fine for most users and rising the value would make gdalwarp a bit slower for everybody who run it with the defaults.