[Proj] Ortho Projection Question
Mikael.Rittri at carmenta.com
Fri Nov 4 12:21:24 EST 2011
In Proj.4, the x_0 and y_0 should be expressed in meters (unless you have an ellipsoid definition in feet, but the predefined ones are in meters).
I am not sure about ESRI, but I suspect that the False Easting and False Northing are expressed in US feet in this case. So you can try to convert them to meters for use in Proj.4.
4 nov 2011 kl. 02:58 skrev "Brian Krzys" <cokrzys at gmail.com>:
> I am trying to duplicate an ESRI "local" projection with Proj.4
> parameters and can't quite get it worked out. The ESRI custom
> projection file has:
> PROJCS["Twin_Creeks_Mine_Grid (Local)",
> The equivalent Proj.4 parameters I've setup are:
> +proj=ortho +datum=NAD27 +lat_0=41.217358 +lon_0=-117.183175
> +x_0=14225.0 +y_0=36603.0 +units=us-ft no_defs
> I want to convert to lat-long WGS84 so I am going to this:
> +proj=longlat +datum=WGS84 +no_defs no_defs
> My input test point is:
> x = 15768.1900000000 y = 65384.1600000000
> In ESRI land I get back (lat-long): 41.160175 -117.177571
> With Proj.4 I am getting: 41.0674232619472 -117.296349865729
> I've also tried this with a couple of specific +to_wgs transformations
> on the ESRI and Proj.4 side and still cannot get the conversions to
> This is all with Proj.4 Rel. 4.7.1, 23 September 2009.
> What I'm wondering about is the ortho "projection" and if there is
> maybe a better option to use? I've searched around the web a bit and
> read about concerns with ortho so also not sure if there is a proj
> update beyond 4.7.1 that might help? I know this whole kind of
> direct-Cartesian conversion isn't the best thing, but generally stuck
> just trying to match what Arc is doing.
> Thanks for the help, Brian.
> Proj mailing list
> Proj at lists.maptools.org
More information about the Proj