[GRASSLIST:8031] Re: Oblique Mercator Projection in GRASS

Morten Hulden morten at untamo.net
Tue Aug 23 13:58:56 EDT 2005

Dave Kindem wrote:

>  From what I can tell, the Proj4 OMERC program accepts parameter  
> information in a two ways:
> --the two point method and
> --the central point and azimuth method.
> Currently, the GRASS seems to accept only two point information, and  
> the State of Michigan publishes central point and azimuth parameters.
> Is there a way to set up an OMERC-based location within GRASS using  the 
> data I have?  Or, alternatively, can the OMERC interface be  modified to 
> accept central point and azimuth parameters in a future  release?

Not quite sure, but I think this restriction only concerns the g.setproj 
program, normally used only when the location is created. After creating 
an omerc-location you should be able to edit the PROJ_INFO file to 
conform to the other method.

Remove the lines starting with lon_1, lon_2, lat_1 and lat_2 and instead 
add two lines with your central point and azimuth parameters:

lonc: <central point longitude>
alpha: <azimuth value>

Don't do this if you already have imported data into your location - 
create another location for testing.

After this change [rv].proj tools /should/ work as normal.

Please let us know if this worked or what error messages you get.


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