No subject

30339 open("foo.png", O_RDONLY) = -1 EFBIG (File too large)

Given that you suggested using an uncompressed format, although a
different one, I assumed that this would be because my gdal was
compiled to use system's libpng, which is unlikely to have large
file support.  So I recompiled gdal with internal PNG support but I
still get the same error.  I guess this means that somehow the PNG
driver does not get compiled with correct definitions.  I do see
calls to stat64 before that open call, so it would seem that some
parts are using 64bit calls.  Unless you have some insight into the
issue, I'll investigate this more closely later today or tomorrow.

I'm still using v1.1.8 but I'll get the CVS version as soon as
possible.

> My suggestion would be to let gdaladdo generate the overviews itself
> unless you have some specific algorithm for generating the overviews
> that you feel strongly about.

It's not really an algorithm issue, the overviews I already have
have been generated from different data and serve much better as
overviews.  If I generated highly downscaled versions of the high
resolution data, I couldn't read text or make much sense of the
data otherwise either.  But I can work around this problem easily
by keeping the overviews in separate files and operating on them as
separate datasets.  I am slightly worried whether GDAL's caching
works well in a situation like this, i.e. is it designed to work
with multiple simultaneously open datasets, but given that I
eventually need multiple simultaneously open datasets anyway
("real" datasets, not just overviews of an other dataset), I guess
I'll just make it work if it doesn't.

-- 
Hannu