[gdal-dev] Border problem with gdal2tiles

[Jorge Arévalo]

Hello,

I'm executing gdal2tiles against 2 different TIFF files. Say
'image1.tiff' and 'image2.tiff'. Image1 size is 3.5 GB, and image2
size is 4.1 GB. Here, links to gdalinfo outputs applied to them:

image1: http://dl.dropbox.com/u/6599273/gdal/gdalinfo_output_image1.txt
image2: http://dl.dropbox.com/u/6599273/gdal/gdalinfo_output_image2.txt

As you can see in the corner coordinates, both images are in this situation:

http://dl.dropbox.com/u/6599273/gdal/images_schema.png

But when you execute gdal2tiles against one, and then gdal2tiles
against the other one, to generate google overlay tiles, they share a
small part. For example, both sets of tiles share a directory 14/8055.
And all the images of these directories are complementary:

image1. Directory 14/8055/10106.png:
http://dl.dropbox.com/u/6599273/gdal/image1_14_8055_10106.png
image2. Directory 14/8055/10106.png:
http://dl.dropbox.com/u/6599273/gdal/image2_14_8055_10106.png

Or graphically, something like this (sorry for the rusty schema, but I
think it shows my point):

http://dl.dropbox.com/u/6599273/gdal/images_schema2.png

Over the map, the problem is visually striking:

http://dl.dropbox.com/u/6599273/gdal/gdal2tiles_border_problem.png

The problem is the border tiles from image2 (geographically placed on
the right side) have their left parts (this is, the 128 pixels from
the left of each border tile) in blank, and they overwrote the border
tiles from image1. Otherwise, the tile 14/8055/10106.png belonging to
image2 overwrote the tile 14/8055/10106.png belonging to image1.

Of course, I could execute gdal2tiles against both images at same
time, constructing a VRT file first. That works fine. But I need to
make it work in the other way, executing gdal2tiles one time per
image, and putting all the tiles together.

One option, not related with GIS at all, could be constructing one
tile for each 2 overlapping tiles, taking the left part from one of
them, and the right part for the other one. But do you have a more
elegant option?

If you need more context or further explanations, don't hesitate to ask me.

Many thanks in advance, and best regards,

-- 
Jorge Arévalo
Internet & Mobility Division, DEIMOS
jorge.arevalo at deimos-space.com
http://es.linkedin.com/in/jorgearevalo80
http://mobility.grupodeimos.com/
http://gis4free.wordpress.com
http://geohash.org/ezjqgrgzz0g