Re: [gdal-dev] gdalwarp over tiles in Plate carée

[Eli Adam]

Kat,

    The only practical way I know to avoid these slivers of
misalignment due to projections having slightly different rotations is
to mosaic first.  I've been able to do that with even extremely large
files with the help the virtual file format (VRT) of GDAL.  If you have
tiles in one projection and want to end with a mosaic in a different
projection, mosaicing first is probably going to be easier and better. 
However, if you need to reproject the tiles first and then mosaic you
can do that.  

    The way I've done that in the past is a lot of work of
reprojecting, then trimming/masking the edges that look bad, then
sometimes making a small mosaic of original tiles for the overlap areas,
reprojecting and trimming that and so on.  It is extremely laborsome and
involves lots of hand entry of coordinates.  Only do that if there is
really no better way.  

    If you can't mosaic first, hopefully someone will suggest a better
method (perhaps better management of nodata values?) that is less work
than what I used to do before gdalbuildvrt.

Best Regards, Eli

> No in my case i want to reproject them first and only then to create
a
> mosaic. (maybe I was not clear on this)

> Hello Eli
> I'm using gdalwarp but I'm getting that "blank" area in the bottom of
my
> image. When I try to mosaic (or visualize) with other tile (also
reprojected
> with gdal) I get this area that was not suppose to have. Any idea how
to
> avoid this?
> Thanks
> Kat
> 
> 2011/7/8 Eli Adam <EAdam at co.lincoln.or.us>
> 
>> >>  Greetings
>> >> I'm using gdalwarp to reproject a few tiles from platecarré to
UTM
>> > WGS84
>> >> (for a specific zone). Originally they are tiles so they don't
have
>> > any
>> >> "blank" space between them but when I reproject to UTM I get a
few
>> > areas in
>> >> the borders of the image. What can I do to still have a perfect
>> > match
>> >> between tiles?
>> >> Thanks
>> >> Kat
>> >
>> > Kat,
>> >
>> >      I think that gdal_retile.py does what you want.  You can
also
>> > mosaic them first either with gdalwarp or (if they are large
files)
>> > gdalbuildvrt and then reproject that one mosaic.  More details
here:
>> > http://gdal.org/gdal_retile.html   
http://gdal.org/gdalbuildvrt.html 
>>
>>
>> I think that I gave incomplete/incorrect information.  To reproject
I
>> think that you will need to do use gdalwarp.  gdal_merge.py is also
>> another way to mosaic.
>>
>> Regards, Eli
>>
>>