Hi Uwe,
<br><br>I have been trying to use gdal_merge.py to merge a few 8 bit colored .tif tiles together. Having tried all sorts of options for this command, I always ended up with a merged 8-bit grayscale picture. I did a search on the internet and found a couple of posts related to this, however it seemed to me that the gdal_merge.py just does not have the ability to preserve the color. Did I get the wrong idea about this? Do you have any suggestion to solve this problem?
<br><br>Not sure if I should post a separate message for this gdal_merge.py issue. I just thought this would be the quickest way to get the help :)
<br><br>Thanks,
<br>Heng
<br>________________________________
<br>From: Schmitz, Uwe [via OSGeo.org] [<a href="/user/SendEmail.jtp?type=node&node=5954287&i=0" target="_top" rel="nofollow">[hidden email]</a>]
<br>Sent: 17 January 2011 09:22
<br>To: Heng Feng
<br>Subject: AW: [gdal-dev] An issue about using GDALWARP to dotheNTv2transformation
<br><br>Heng,
<br><br>> Hi Uwe,
<br>>
<br>> Hope you had a wonderful Christmas break.
<br><br>Yes, thank you (but I have the impression that mine has
<br>been shorter than yours ;-))
<br><div class='shrinkable-quote'><br>> Regarding the issue about the NTv2 transformation,
<br>> the map data provider has confirmed that the raster
<br>> data do cover some areas which are outside the Germany
<br>> map, hence the area of the grid shift file. I have
<br>> taken your second suggestion and ignore the coordinates
<br>> outside BeTA2007 grid. However, by running the suggested
<br>> command on some raster data, this time I have got the
<br>> message "Inverse grid shift iteration failed, presumably
<br>> at grid edge. Using first approximation." Do you know
<br>> why I am having this message? Do I need to worry about it?
<br>>
</div>No! NTv2 is based on a grid of shift values from System A
<br>to System B (DHDN -> ETRS89 in your case). For the other
<br>direction (B->A, or ETRS89->DHDN) the shift value is
<br>calculated by an iterative approach. Near the grid edges it's
<br>possible that during the iteartion the coordinates fall
<br>outside the grid. I would imagine that this is the case
<br>for the message you see.
<br><br>Assuming you don't need precise transformation results
<br>outside the BeTA2007 grid, you can safely ignore this
<br>message.
<br><br>Regards
<br>Uwe
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