I think many would agree! Thanks Frank and Howard!! David C Finnegan Research Physical Scientist CRREL --------- Message sent via my BlackBerry Wireless Device
----- Original Message ----- From: [email protected] <[email protected]> To: Frank Warmerdam <[email protected]> Cc: [email protected] <[email protected]> Sent: Mon Sep 20 21:53:40 2010 Subject: Re: [Liblas-devel] Vertical Datum Developments Not exciting? This is extremely exciting! Thanks Frank. Michael Smith US Army Corps of Engineers Hanover, NH Remote Sensing/GIS Center On Sep 20, 2010, at 7:47 PM, "Frank Warmerdam" <[email protected]> wrote: > Folks, > > I owe you all (and Howard and Mike in particular) a status report on my > vertical datum support efforts for liblas and other client libraries and > applications. > > First, I will refer you to the RFC I wrote in the spring related to vertical > coordinate system support at: > > http://liblas.org/development/rfc/rfc_1_verticalcs.html > > That was implemented, but recently I have added some additional work, aiming > to actually support applying vertical datum shifts as part of a reprojection > operation with liblas (ie. las2las). > > The key elements in this are: > > 1) PROJ.4 has been upgraded to support a +geoidgrids= parameter which can > reference one or more geoid files relating geoid heights to WGS84 ellipsoidal > heights. These are used to transform back and forth to/from geoidal vertical > datums like NAVD88. > > 2) Some geoid files in the .gtx format have been assembled at the following > url, notably US files from NOAA suitable for use for NAVD88 and global > models from NGA suitable for approximating other geoidal coordinate systems > world wide. > > http://download.osgeo.org/proj/vdatum > > 3) Libgeotiff's EPSG to csv translation script was upgraded to capture some > information about EPSG vertical coordinate systems, and compound coordinate > systems (in vertcs.csv and compdcs.csv respectively). The vertcs.csv includes > a column indicating what .gtx transformation files can be used to get from > a given vertical datum to WGS84 ellipsoidal. This has been forcably > populated for NAVD88 and "EGM96 Geoid Height". > > 4) GDAL/OGR's OGRSpatialReference object has been extended to support > importing vertical and compound coordinate systems with importFromEPSG(). > A new EXTENSION node on the VERT_DATUM object can be used to list > geoid grid shift files. > > 5) GDAL/OGR's OGRSpatialReference::SetFromUserInput() method has been > extended to allow defining a compound coordinate system from any > EPSG vertical coordinate system and any (GCS or PCS) horizontal coordinate > system using the form EPSG:4326+5703 (WGS84 + NAVD88 in this case). > > 6) OGRSpatialReference's from and to PROJ.4 functions have been updated > to support the +geoidgrids= and corresponding WKT EXTENSION node. > > 7) The GeoTIFF to WKT translation code now uses definitions from vertcs.csv > when available which also picks up the geoid grid files. > > 8) liblas has been updated to use the latest geotiff translation code > and to ensure that "eCompoundOK" forms of WKT are used for translation > too and from proj.4 format so we get the geoidgrids. > > As a result of the above, if you were to build liblas, GDAL, PROJ.4, > and perhaps libgeotiff from SVN "trunk" of each project, and ensure you > populated your PROJ.4 grid shift file directory (ie. /usr/local/share/proj) > with the appropriate grid shift files you could do: > > las2las -t_srs WGS84 srs_vertcs.las wgs84_ellipsoidal.las > > and transform the sample srs_vertcs.las file from NAVD88 geoidal > heights to WGS84 with WGS84 ellipsoidal heights! That may not seem > that exciting to you but for me it's a milestone. > > I have a variety of cleanup, documentation, and validation to do, > but I feel the essentials of my project are now in place. Testing > and feedback are welcome, though you might want to wait till I have > better documentation in place. > > Best regards, > -- > ---------------------------------------+------------------------------------- - > I set the clouds in motion - turn up | Frank Warmerdam, [email protected] > light and sound - activate the windows | http://pobox.com/~warmerdam > and watch the world go round - Rush | Geospatial Programmer for Rent > > _______________________________________________ > Liblas-devel mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/liblas-devel _______________________________________________ Liblas-devel mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/liblas-devel _______________________________________________ Liblas-devel mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/liblas-devel
