AW: [gdal-dev] An issue about using GDALWARP todotheNTv2transformation

[Schmitz, Uwe]

Heng,
> 
> Hi Uwe,
> 
> Sorry to bother you again. I actually need your help 
> about another GDALWARP problem I am having. I just 
> thought it might be better to send you an email 
> directly about this (a shortcutJ) although I did 
> just post a message regarding this problem on 
> the GDAL DEV forum: 
> http://osgeo-org.1803224.n2.nabble.com/gdalwarp-reprojection-problem-td6030749.html.
> 
> I am just wondering whether you have seen this kind 
> of problem before. Do you have idea about what 
> could be the cause for this problem?
>
personally I try to avoid large data sets in
one file. I tend to put them in many smaller manageable
tiles. So may be I'm not the right one to ask for
help (especially if you hit a real bug ;-)) in this case.
But there are many people here with deep knowledge of
such things, that I'm pretty sure you will get
further help from them.

So let me try to get some more informations regarding
your above mentioned posting. What do you mean by
"large" data. Are you beyond 65k-Pixel in width or
height, so that you need BigTIFF? 
You wrote:
"... the output pictures seemed to contain the gaps, 
which appeared to be a few horizontal lines when zooming out."

I would assume that the gaps will disappear or even come
up randomly if you zoom out (according to which interpolation
algorithm your favorite viewer uses). But may be I haven't
the right impression of what you mean with "gap".

Further, if I have to do gdalwarp, I will take two
steps:
   1. gdalwarp to an intermediate file with a fast and
      "easy" compression (uncompressed if you can afford
      the space)
   2. gdal_translate the intermediate file to the target file
      with the desired format and compression
I don't know if these two steps are still necessary.


Uwe