Changes between Version 2 and Version 3 of UserDocs/GdalWarp

Timestamp:

Dec 6, 2007, 1:45:27 PM (16 years ago)

Author:

maphew

Comment:

added example for setting nodata flag in multiple images

UserDocs/GdalWarp

@@ -6 +6 @@
 [[PageOutline(2-6,,inline)]]
 
-=== Will increasing RAM increase the speed of gdalwarp? ===
+== What if '''nodata''' is different in each image? ==
+
+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:
+
+{{{
+# for this image we want to ignore black (0)
+gdalwarp -srcnodata 0 -dstnodata 0 orig-ignore-black.tif black-nodata.tif
+
+# and now we want to ignore white (0)
+gdalwarp -srcnodata 255 -dstnodata 255 orig-ignore-white.tif white-nodata.tif
+
+# and finally ignore a particular blue-grey (RGB 125 125 150)
+gdalwarp -srcnodata "125 125 150" -dstnodata "125 125 150" orig-ignore-grey.tif grey-nodata.tif
+
+# now we can mosaic them all and not worry about nodata parameters
+gdalwarp black-nodata.tif grey-nodata.tif white-nodata.tif final-mosaic.tif
+}}}
+  
+
+
+== Will increasing RAM increase the speed of gdalwarp? ==
 
 Adding ram will almost certainly increase the speed.  That’s not at all the same as saying that it is worth it, or that the speed increase will be significant. Disks are the slowest part of the process.
@@ -20 +40 @@
 
 
-==== Warp and Cache Memory: Technical Details ====
+=== Warp and Cache Memory: Technical Details ===
 
 The GDAL_CACHEMAX affects the amount of space reserved for the low