| 7 | | |
| 8 | | == What if '''nodata''' is different in each image? == |
| 9 | | |
| 10 | | If the ''nodata'' tag is set in the geotiff header, gdalwarp will use it automatically, you don't need to do anything. However, `-srcnodata` overrides this, so if you are handling a bunch of images with different values to be ignored you need to either a) pre-process them to have the same to-be-ignored value, or b) set the nodata flag for each file. Use (b) if you need to preserve the original values for some reason, for example: |
| 11 | | |
| 12 | | {{{ |
| 13 | | # for this image we want to ignore black (0) |
| 14 | | gdalwarp -srcnodata 0 -dstnodata 0 orig-ignore-black.tif black-nodata.tif |
| 15 | | |
| 16 | | # and now we want to ignore white (0) |
| 17 | | gdalwarp -srcnodata 255 -dstnodata 255 orig-ignore-white.tif white-nodata.tif |
| 18 | | |
| 19 | | # and finally ignore a particular blue-grey (RGB 125 125 150) |
| 20 | | gdalwarp -srcnodata "125 125 150" -dstnodata "125 125 150" orig-ignore-grey.tif grey-nodata.tif |
| 21 | | |
| 22 | | # now we can mosaic them all and not worry about nodata parameters |
| 23 | | gdalwarp -dstnodata 0 black-nodata.tif grey-nodata.tif white-nodata.tif final-mosaic.tif |
| 24 | | }}} |
| 25 | | |
| 26 | | If you are wondering why the `-dstnodata` is there, it's because although gdalwarp automatically honours input nodata, but before GDAL 1.11, it didn't carry that through unless instructed up. |
