Changes between Version 13 and Version 14 of UserDocs/GdalWarp

Timestamp:

Dec 26, 2014, 3:35:14 AM (9 years ago)

Author:

Even Rouault

Comment:

Some updates related to gdalwarp

UserDocs/GdalWarp

@@ -24 +24 @@
 }}}
   
-If you are wondering why the `-dstnodata` is there, it's because although gdalwarp automatically honours  input nodata, it doesn't carry that through unless instructed.
-
+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.
 
 == Will increasing RAM increase the speed of gdalwarp? ==
@@ -122 +121 @@
 ''When I compress an image with gdalwarp the result is often many times larger than the original! ''
 
-Note : with GDAL 1.7.2, the situation can be improved by using the [http://gdal.org/structGDALWarpOptions.html#0ed77f9917bb96c7a9aabd73d4d06e08 OPTIMIZE_SIZE warping option], so the following statements no really longer apply.
+By default gdalwarp operates on chunks that are not necessarily aligned with the boundaries of the
+blocks/tiles/strips of the output format, so this might cause repeated compression/decompression of
+partial blocks, leading to lost space in the output format.
 
-The nature of gdalwarp and compression are fundamentally at odds with eath other, there is no fix forthcoming. The recommendation is to use gdalwarp without compression and then follow up with gdal_translate with compression:
+The situation can be improved by using the [http://gdal.org/structGDALWarpOptions.html#0ed77f9917bb96c7a9aabd73d4d06e08 OPTIMIZE_SIZE warping option],
+but not that depending on the source and target projections, it might also significantly slow down
+the warping process.
+
+Another possibility is to use gdalwarp without compression and then follow up with gdal_translate with compression:
 {{{
 gdalwarp infile tempfile.tif ...options...
 gdal_translate tempfile.tif outfile.tif -co compress=lzw ...etc.
 }}}
-
-See ticket:1688 and linked discussions for a fuller explanation.
 
 Alternatively, you can use a VRT file as the output format of gdalwarp. The VRT file is just an XML file that will be created immediately. The gdal_translate operations will be of course a bit slower as it will do the real warping operation.