Re: [Viking-devel] Viking 1.0.2 and 1.1 Projections
FWIW: I tried converting the gpx files from WGS84 to NAD27 and using the geotiffs with those tracks under viking. That still didn't work, even though the gpx transforms looked correct. That may be because NAD27 uses a different ellipsoid, so converting coordinates that are in NAD27 but treated as WGS84 to WGS84 UTM does not give you the NAD27 UTM coordinates. IIRC this effect is bigger than the actual surface datum shift in meters. I have the gpsbabel scripts I used for that if any one is interested. Basically one has to use gpsbabel to convert to unicsv and then make a new unicsv with the datum transform then conver the unicsv back to gpx. So, next I tried converting the World File (tfw) for the geotiff from NAD27 to WGS84. That seems to work. So then you have the geotiffs georeferenced in WGS84. But, it is lined up with the NAD27 UTM grid instead of the WGS84 UTM grid. That's probably not detectable. I had been thinking about how to do this right, within viking. Transforming the way the map lines up makes more sense, since then you can alpha composite with other maps. So, having a projection selector for georeferenced maps and transforming the origin of the world file on read seems like a plausible approach. pgpoSJVa52QAd.pgp Description: PGP signature -- Achieve unprecedented app performance and reliability What every C/C++ and Fortran developer should know. Learn how Intel has extended the reach of its next-generation tools to help boost performance applications - inlcuding clusters. http://p.sf.net/sfu/intel-dev2devmay___ Viking-devel mailing list Viking-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viking-devel Viking home page: http://viking.sf.net/
Re: [Viking-devel] Viking 1.0.2 and 1.1 Projections
FWIW: I tried converting the gpx files from WGS84 to NAD27 and using the geotiffs with those tracks under viking. That still didn't work, even though the gpx transforms looked correct. I have the gpsbabel scripts I used for that if any one is interested. Basically one has to use gpsbabel to convert to unicsv and then make a new unicsv with the datum transform then conver the unicsv back to gpx. So, next I tried converting the World File (tfw) for the geotiff from NAD27 to WGS84. That seems to work. I wrote a script that will generate the tfw from the tif in place with a _WGS.tfw extension. It is attached if anyone is interested in using geotiffs with viking (and no proj4/gdal support in viking). You may have to edit the proj4 options to reflect the area you are concerned with. The parameters I used are for my area. Harry McGavran vikingtfw.sh Description: vikingtfw.sh Harry G. McGavran, Jr. E-mail: w5...@w5pny.com -- Achieve unprecedented app performance and reliability What every C/C++ and Fortran developer should know. Learn how Intel has extended the reach of its next-generation tools to help boost performance applications - inlcuding clusters. http://p.sf.net/sfu/intel-dev2devmay___ Viking-devel mailing list Viking-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viking-devel Viking home page: http://viking.sf.net/
Re: [Viking-devel] Viking 1.0.2 and 1.1 Projections
I haven't tried geotiff, but I do have DRG images for my region (in NAD27). If you could send a note how you configure that, I'll try it. I wonder if viking should depend on proj. pgpTNWHc5IXqh.pgp Description: PGP signature -- Achieve unprecedented app performance and reliability What every C/C++ and Fortran developer should know. Learn how Intel has extended the reach of its next-generation tools to help boost performance applications - inlcuding clusters. http://p.sf.net/sfu/intel-dev2devmay___ Viking-devel mailing list Viking-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viking-devel Viking home page: http://viking.sf.net/
Re: [Viking-devel] Viking 1.0.2 and 1.1 Projections
Guilhem Bonnefille guilhem.bonnefi...@gmail.com writes: 2011/5/14 Greg Troxel g...@ir.bbn.com: I haven't tried geotiff, but I do have DRG images for my region (in NAD27). If you could send a note how you configure that, I'll try it. I don't know what NAD27 is. AFAIK, currently, viking only support 3 projections: UTM, Mercator and LatLon (I don't have corresponding codes as I' writing). Those are projections, which are ways to convert coordinates in lat/lon to numbers on some plane. NAD27 is a datum, which is a separate concept, about how particular lat/lon coordinates are assigned to particular places. Today, WGS84 is used for most things, and it's ~= to ITRF00 at the few mm level. There is also NAD83, the official datum of the US, which is a few meters different, and other datums in other places around the world. NAD27 is from 1927, and coordinates differ by tens of meters. It was the official datum of the US before NAD83, and many USGS topo maps are in NAD27. Plus NAD27 uses a different ellipsoid. So one has to transform to/from WGS84 to NAD27 to use USGS DRGs with GPS data. What I don't understand is how this ever worked. I wonder if the GPS data had been transformed to NAD27?? Perhaps gpsbabel can do that. Long term, viking should be projection and datum aware. I wonder if viking should depend on proj. I think so. I started to look a the proj4 library, but it is certainly a significant change, reclaiming long time invest. And I don't have this time currently. But proj support will certainly be a great add. Anynbody working on this would gain all my support. Note that I started to wrote notes about this on the following wiki page: https://sourceforge.net/apps/mediawiki/viking/index.php?title=Idea:gdal Feel free to contribute (on code or on this page). I have used proj, and it's pretty easy. The key question is if it's ok to depend on it, which requires anyone using viking to have it. But I think most geo software does already. I am generally in favor of requiring it, but I think we should understand/plan a bit better first. pgp095ZlGDzHh.pgp Description: PGP signature -- Achieve unprecedented app performance and reliability What every C/C++ and Fortran developer should know. Learn how Intel has extended the reach of its next-generation tools to help boost performance applications - inlcuding clusters. http://p.sf.net/sfu/intel-dev2devmay___ Viking-devel mailing list Viking-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viking-devel Viking home page: http://viking.sf.net/
[Viking-devel] Viking 1.0.2 and 1.1 Projections
It has been since 2009 that I last used viking. At that time I contributed some magic-scissors patches that were incorporated into viking. For various reasons I tried the latest two versions and had a problem I didn't have with whatever version was current in 2009. I use geotiffs in combination with gpx file tracks and waypoints. When I load a geotiff (and it's corresponding tfw file) and load the gpx file, the tracks and waypoints are shifted to the northeast by an amount that corresponds to using the wrong projection on one or the other layer. geotiffs are NAD27 and gpx files are WGS85. What is the status of resolving this difference with viking??? I don't remember having this problem in 2009 and I don't see anything that allows me to set the projection for a layer to overide what viking has chosen. Harry McGavran -- Harry G. McGavran, Jr. E-mail: w5...@w5pny.com -- Achieve unprecedented app performance and reliability What every C/C++ and Fortran developer should know. Learn how Intel has extended the reach of its next-generation tools to help boost performance applications - inlcuding clusters. http://p.sf.net/sfu/intel-dev2devmay ___ Viking-devel mailing list Viking-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/viking-devel Viking home page: http://viking.sf.net/
