[Gdal-dev] Question on building external overviews

[Stephen Woodbridge]

Frank Warmerdam wrote:
> Stephen Woodbridge wrote:
>> Hi guys,
>>
>> I took this approach to building external overviews, but all my images 
>> seem to be gray in mapserver and appear to be all nodata values in the 
>> file. Any idea what I'm doing wrong here?
>>
>> I have a directory of of 16x16 tiles that fill a one degree block.
>> I want to make 4x4 overview files with 4x4 of the original tiles.
>> ie: 4x4 original tiles into 1 overview
>>
>> So for the first tile, I create the output tile like this
>>
>> gdal_translate -of GTiff -co \"TILED=YES\" -outsize 3200 3200 -a_srs 
>> EPSG:4326 -a_nodata 0 -a_ullr $top $left $bot $right $inf $outf

I set $top $left $bot $right to the extents shown in the gdalinfo in the 
prior post, which is 4 times larger in x and y then the original tiles 
and $inf is one of the original tiles that is 1/16 the size of the 
output area.

>> then for each additional tile I mosaic them into $outf like this:
>>
>> gdalwarp --config GDAL_ONE_BIG_READ ON -srcnodata 0 -rc -wm 150 $inf 
>> $outf

Again $inf is one of the original tile that are 1/16 the size of the 
output area.

>> Any help would be appreciated.
> 
> Steve,
> 
> I don't see any obvious problem with the process.  When you say they are
> grey in mapserver, do you mean "greyscale" or a single constant grey?

a single constant grey

> If you can reproduce the problem with a small dataset I would be happy to
> try it here and comment.

I will see if I can do that with just 2 input files.

Thank you,
   -Steve