Frank, Thanks for the references... I will look them over. I am correct that the c# binding will not have access to the Geod calc's?
David David M. Baker Senior Geologist - Chief Technology Advisor Chesapeake Energy Corporation 405-935-3715 office 405-496-5373 cell [email protected] -----Original Message----- From: Frank Warmerdam [mailto:[email protected]] Sent: Tuesday, March 16, 2010 4:13 PM To: David Baker (Geoscience) Cc: '[email protected]' Subject: Re: [gdal-dev] Geodetic Problem David Baker (Geoscience) wrote: > Frank and the List, > > > > I have a geodetic problem I hope GDAL/OGR can solve. > > > > The setup: > > > > I have two radio towers each the same height and at the same elevation > being 10,000 meters apart. I know the latitude and longitude of the > first tower and those coordinates reference WGS84 (though they could be > any geographic CRS, NAD27, NAD83, etc.). I also now the baring to the > second from the first measured from true north at the first tower. > > > > The problem: > > > > Given the above information and using the prebuilt tools, GDAL/OGR > utilities, what workflow would one use to calculate the latitude and > longitude of the second tower? > > > > The hints I have gotten so far say to use a conformal projection (UTM > maybe?) centered at the first point with a scale factor of 1, a local > projection. Calculate the Cartesian offsets from the first point to the > second based on the azimuth of the given baring. Using the baring > calculate the x and y offsets to the second point and use offsets to > find the x and y of the second point in the local coordinate system. > Then, reproject the x and y of the second point to the latitude and > longitude in the CRS of the first points latitude and longitude. If > this is correct, I guess the question is, what would the proj4 > parameters be for such a local projections. David, The above will give a pretty good approximation, degrading as the distance increases. However, the proper way to do this is using great circle operations. The PROJ.4 "geod" program can do this: http://trac.osgeo.org/proj/wiki/man_geod There is more information on geodesic operations at: http://trac.osgeo.org/proj/wiki/GeodesicCalculations 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 This email (and attachments if any) is intended only for the use of the individual or entity to which it is addressed, and may contain information that is privileged, confidential and exempt from disclosure under applicable law. If the reader of this email is not the intended recipient, or the employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately by return email and destroy all copies of the email (and attachments if any). _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
