Hi Andrew,

On 7-3-2013 22:44, Andrew Hundt wrote:

Essentially, I would like to define the origin of a projected coordinate system to be A WGS84 lat long coordinate I pass in. Unfortunately standard UTM zones aren't accurate enough so I need to set the origin using the current lat/lon location at startup then do conversions using that.

It looks like latlon.h and tmerc.h are what I want, how would I specify the lat/lon I want for the origin? Or is this perhaps not part of the embedded functionality?

I've been looking at the examples, and it appears the conversions are mostly for lat-lon rather than lat-lon-altitude. Is it possible to handle points with altitude? If not, it looks like altitude conversions can be done with a simple offset when converting meters to meters, is that accurate?

Also, would these conversion extensions be safe to use? I noticed the following comment in one of the examples:

// BSG 28-10-2010

// TODO: clear up this test

// it is more a test than an example

// the results are sometimes WRONG

That was me :-) Years ago indeed.

Yes, it still has to be done, the projections were not worked on for a long time.

The projections themselves are ported from PROJ4 and basically safe to use indeed (with no guarantee as usual in open source). I did make a lot of unit tests, projecting forward and backward, and checking the results. During this I found about five errors which I reported to PROJ4 and to Gerald Evenden, and which were quickly fixed by them. So we cover some tests which were never done before ;-)

Altitude is not yet supported in the projections. Altitude/Z can be part of the point, but it is not changed when projecting a point.

About latlon.h, tmerc.h, do you mean latlong.hpp? Probably yes, and tmerc.hpp. I don't know by head how to do this, basically it follows PROJ4 and their documentation is the best starting point. So I point you to that first http://trac.osgeo.org/proj/

Thank you for all of your help with this.

You are welcome.

Regards, Barend