[Proj] Ortho Projection Question

[Mikael Rittri]

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.

Regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

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)",
> GEOGCS["GCS_North_American_1927",
> DATUM["D_North_American_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],
> PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433]],
> PROJECTION["Local"],
> PARAMETER["False_Easting",14225.0],
> PARAMETER["False_Northing",36603.0],
> PARAMETER["Scale_Factor",1.0],
> PARAMETER["Azimuth",0.0],
> PARAMETER["Longitude_Of_Center",-117.183175],
> PARAMETER["Latitude_Of_Center",41.217358],
> UNIT["Foot_US",0.3048006096012192]]
> 
> 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
> match.
> 
> 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.
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