Last week I asked the list for help with using GeoTIFF images in MapInfo. I was using the Georeg tool supplied with MapInfo to register images created in Erdas Imagine, but the tool was refusing to register my images. Thanks to Bill Wemple for his complete solution to the problem, and an overview of using GeoTIFFs in MapInfo. Well worth a read if you are having similar problems - I have put the complete explanation below: This Geotiff image is using a User-defined PCS (Projected Coordinate system) code as I guessed. The PCS number for this image is 32767 which is categorized as a custom\user defined system. It's one that does not follow the EPSG standards for this particular coordinate system used for geotiffs. It's not invalid, but our georeg tool only uses the standard EPSG codes. You can go here to look up specifics if you like: http://www.remotesensing.org/geotiff/geotiff.html Here's the entry from the official docs I got in our knowledgebase we publish on the web in our support section: <snip> The current GEOREG.MBX tool is only able to register GeoTIFF images which are defined by using a projected Coordinate System code. Supported GeoTIFF images will include a PCS (Projected Coordinate System) code which is a number that corresponds to a specific Projected Coordinate System. In order for the GEOREG.MBX tool to register the image, the PCS code must be defined within the MAPINFOW.PRJ file (delimited by "\p" and containing a value between 20000 and 32760). MapInfo only supports a subset of these. If the PCS specified in the GeoTIFF file is one MapInfo does not support, GEOREG.MBX will display a message stating that the raster image could not be registered. <snip> You can create a custom projection entry to register these images automatically though, and use it with the georeg.mbx tool. Whenever the tool reads the geotiff header, it first finds the PCS code, then tries to match it up with one from the mapinfow.prj file. The mapinfow.prj file has a whole bunch of entries in it that have a \p#### in the quoted name part of the entry. When the tool finds a matching \p### code, it uses the projection parameters of that entry to create control points in the *.tab file using the image control point values to register the image in that Projection\Coordinate system. This geotiff file is uses a custom PCS code (32767) which doesn't fall in the range of ones we support as it's user-defined. We can create one like I did below for this image though. A custom PCS code in a geotiff can be basically used for any projection, known or unknown to us. ESRI must be doing things a bit differently in reading geotiffs and going further into the image tags than our tool is doing. I might have to get Development to look into this a bit further. Our code is a bit more simplistic I guess, but it does work OK once you get the gist of what's going on. I added the mapinfow.prj file entry below which is using the custom PCS code and the projection parameters you supplied me. When the georeg.mbx tool is run on this image now, it automatically created the TAB file in this OSGB projection and the raster sits in South Central England near the coast about 18.3 miles east of Southampton (is this where it's supposed to be?). "--- Custom Geotiff Projections ---" "Custom OSGB TM (Airy)\p32767", 8, 79, 7, -2, 49, .99996012717, 400000, -100000 There is a caveat here to remember. This entry from the mapinfow.prj file with the \p32767 code will be used with these custom projection parameters everytime you open geotiffs with the same 32767 pcs code in them unless you edit the PRJ file to use different parameters with this same user-defined PCS code. You could also just add new entries with differing parameters and just add\remove the \p327676 code from the PRJ file entry depending on which system you are trying to register your images with using georeg.mbx and a user-defined geotiff PCS code. Once the Tab file is created, we don't really care what PCS code the image has in it anymore, we just use the control points and coordinate system from the Tab file. This registration only has to be done once to create the TAB file which MapInfo will use to open the image afterwards. Hope this helps, -Bill --------------------- Ben Barton [EMAIL PROTECTED] _______________________________________________________________________ List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MapInfo-L" in the message body.
