I am currently using GRASS 6.1.cvs, installed from Lorenzo Moretti's site.
I'm working with data from the State of Michigan Geographic Data Library, which is published in the Michigan GeoRef system, based on an Oblique Mercator projection [http://www.michigan.gov/documents/DNR_Map_Proj_and_MI_Georef_Info_20889_7.pdf\]
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?
Dave Kindem
Grand Haven, Michigan
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.
rgds
Morten