[Gdal-dev] Help with overviews/pyramids

[Bill Binko]

Hi everyone,

(I'm posting this here first, as I believe it's more Raster related than 
Mapserver, but I may post it there too)

I have DOQQs for a large portion of Florida in ECW format.  I just wrote a 
small utility that fixed the projection that they had, and gdalinfo 
correcly reads their info now, but I cannot seem to get gdal_merge.py to 
create a summary image.

I know the terms summary/overview/pyramids are overused (and misused by 
me), so here's what I want.  If someone can help me through this, I'll be 
happy write a script and a HOWTO to feed back to the community.

I would like to run a script to generate lower granularity ("zoomed out") 
versions of these files.  I would like them to be georeferenced, and I 
would like a Mapserver TILEINDEX for them.  

I am not looking for adding overviews into the files (gdaladdo) since ECW 
files have that already.  I would like the separate layer(s) so that my 
application performs at any zoom level.

I have heard theorhetical discussions about how to do this ("Zoom out 
until it gets slow, then use that zoom level and make another layer"), and 
I get it.  I even thought I understood how to do this with gdal_merge.py.  
However, when I run it against my ECWs even to just get a single low-res 
summary image, I get this:

$> gdal_merge.py -o overview.tiff -ps 10 10 -v `ls -1 dq*.ecw | head -10`

ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 704
ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 705

....Hundreds of these lines....

ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 706
ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 707
ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 708
ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 709
ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 710
ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 711
ERROR 1: overview.tiff:Error updating TIFF header
ERROR 1: TIFFAppendToStrip:overview.tiff: Write error at scanline 711

It does leave me with a tiff file, but it's not usable (all black with no 
georeferencing).

I'm a bit frustrated.  I thought this was because of the missing 
projections in the ECW, and I have spent alot of time fixing that.  
However, I'm still stuck :-(

Can anyone help?

Thanks
Bill