Hi Uwe, Hope you had a wonderful Christmas break.
Regarding the issue about the NTv2 transformation, the map data provider has confirmed that the raster data do cover some areas which are outside the Germany map, hence the area of the grid shift file. I have taken your second suggestion and ignore the coordinates outside BeTA2007 grid. However, by running the suggested command on some raster data, this time I have got the message "Inverse grid shift iteration failed, presumably at grid edge. Using first approximation." Do you know why I am having this message? Do I need to worry about it? Thanks & BR, Heng From: Uwe Schmitz [via OSGeo.org] [mailto:ml-node+5862681-1425697383-308...@n2.nabble.com] Sent: 23 December 2010 19:47 To: Heng Feng Subject: RE: [gdal-dev] An issue about using GDALWARP to do theNTv2transformation Heng, heng.feng wrote: Hi Uwe, Thanks for your reply. The l0.tif file does not contain any georeferenced information. However, I have run the GDALINFO command on another raster data file which is in the same map data set provided by the customer and hence is supposed to be georeferenced in the way as the l0.tif file. The command output is sent as attached. As mentioned before, I also did the NTv2 transformation on this raster data file (Notrufzonen_50m_v11_6_EPOS.tif) with the same GDALWARP command and the same grid shift file. I also got a lot of error messages saying that some coordinates are outside the area of the grid shift file. And with the "+x_0=500000" parameter, the output error messages are much less than the ones with the "+x_0=4500000" parameter. Thanks for your help again. from your screenshot I see that georeference information of your file seems to be OK. So forget about my comment about missing meridian prefixes, that's not the case. But ..., your file is very large (the extent, not the size). Please notice, that due to the nature of the NTv2 approach it is not possible to calculate coordinates outside the extent of the grid. The BeTA2007 grid covers longitudes between 5d30' to 15d40' East. Your Screenshot of gdalinfo shows that the longitude of the upper left corner is 4d54'45.24" East and hence outside the BeTA2007 grid. OK, what can you do? BeTA2007 has submeter accuracy and I believe, that you don't need it for you data (one pixel covers 50m*50m). So you can try the 7-Parameter Helmert approach described by EPSG::1776 with "+towgs84=..." Parameter instead of "+nadgrids=...". This will result in errors of max. 3m in comparison to BeTA2007. Not that bad for your data ;-) Another way is to specify the "null" grid as fall back for coordinates outside the BeTA2007 grid, like so: ... +nadgrids=C:\fh\comar ch\BETA2007.gsb,null But be aware that coordinates outside the BeTA2007 grid experience no datum shift. This may result in errors up to 200m. Hope that helps. Regards Uwe ________________________________ View message @ http://osgeo-org.1803224.n2.nabble.com/An-issue-about-using-GDALWARP-to-do-the-NTv2-transformation-tp5838904p5862681.html To unsubscribe from An issue about using GDALWARP to do the NTv2 transformation, click here<http://osgeo-org.1803224.n2.nabble.com/template/NamlServlet.jtp?macro=unsubscribe_by_code&node=5838904&code=aGVuZy5mZW5nQGFpcmNvbWludGVybmF0aW9uYWwuY29tfDU4Mzg5MDR8MTI3MzEwMjEw>. AIRCOM International Mobile World Congress 2011, 14-17 February Stand 1B14, Barcelona, Spain Click mailto:eve...@aircominternational.com?subject=Mobile%20World%20Congress%20'11%20meeting%20-%20%Appointement%20%Booking to book a meeting Disclaimer: This e-mail message is confidential and should not be used by, or disclosed to, anyone except the addressee. If you receive this message in error, please advise us immediately on +44 (0) 1932 442000. Since e-mail transmission is not secure or error free, we do not accept responsibility for changes to any e-mail which occur after it has been sent. Attachments to this e-mail may contain software viruses which could damage your systems. You should therefore virus-check all attachments before opening. AIRCOM may monitor incoming and outgoing emails through its networks and by responding to this email, you consent to such monitoring. The views and opinions expressed in this e-mail are those of the author only and not of AIRCOM. We do not intend to enter into any legal commitments or contracts by e-mail. Registered Office: Cassini Court, Randalls Research Park, Randalls Way, Leatherhead, Surrey, KT22 7TW, UK. AIRCOM International Ltd registered in England No. 3052022. VAT number 811 5323 68. Save a tree. Don't print this e-mail unless it's really necessary -- View this message in context: http://osgeo-org.1803224.n2.nabble.com/An-issue-about-using-GDALWARP-to-do-the-NTv2-transformation-tp5838904p5924890.html Sent from the GDAL - Dev mailing list archive at Nabble.com.
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