[GRASS5] Re: [GRASSLIST:8031] Re: Oblique Mercator Projection in GRASS

Morten Hulden morten at untamo.net
Wed Aug 24 10:20:29 EDT 2005

Paul Kelly wrote:
> On Wed, 24 Aug 2005, Morten Hulden wrote:
>> I just tested an omerc_michigan PROJ_INFO file with the alternative 
>> projection parameters and it does not work - the alpha: key-value pair 
>> mysteriously disappers somewhere in the subroutines that construct the 
>> proj command.
>> As a matter of fact /any/ key-value pair in the PROJ_INFO file 
>> starting with either "a" or "f" will fail to show up in the 
>> constructed proj commmand, except "a:" and "f: of course". Could this 
>> have something to do with the routines extracting ellipse parameters? 
>> Like discarding or not looking further into the projinfo stucture if 
>> first char of a key is "a" or "f"?
> Yes indeed I think you're right---and it looks like this bug has been 
> there for 10-15 years!
> The problem is the use of strncmp() in lib/proj/get_proj.c which only 
> checks the first few characters of a string for a match--resulting in a 
> matching any parameter beginning with a, etc.
> I have committed a fix to CVS; please test.

OK, proj-tools working now. I don't have any good maps of Michigan to 
play around with so I'm not sure if the no_rot, no_uoff, rot_conv 
booleans should be defined or not. But I guess Dave will find out once 
he gets his Grass fixed.


>> name: Oblique Mercator
>> datum: nad83
>> towgs84: 0.000,0.000,0.000
>> proj: omerc
>> ellps: grs80
>> a: 6378137.0000000000
>> es: 0.0066943800
>> f: 298.2572221010
>> lat_0: 45.3091666667
>> lonc: -86.0000000000
>> alpha: 337.25556
>> k_0: 0.9996000000
>> x_0: 2546731.496
>> y_0: -4354009.816
>> no_rot: defined
>> no_uoff: defined
>> rot_conv: defined

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