[Proj] Re: Oblique Parameter Question

Gerald I. Evenden gerald.evenden at verizon.net
Fri Oct 28 22:08:50 EDT 2005

On Friday 28 October 2005 09:37 pm, Mike Darweesh wrote:
> Hi All,
> Michael and I are trying to learn about the ob_tran projection in order to
> facilitate use here at the Mars Space Flight Facility. We need more
> information about the o_lon_p and o_lat_p parameters. Could someone give an
> exact English description of how they operate or a URL to such. We
> understand the notion of an oblique projection, but we're having a hard
> time understanding how these parameters define the "obliqueness". We
> applying these to eqc (Platte Caree) if that simplifies your answer at all.
> Thanks,
> -Mike and Michael

Chapter 9 of the libproj4 manual is about the best I can do but I understand 
your frustration.  After spending a few days with it and a little trial and 
error one should develop a "feel" for the subject.

Hopefully, you have a setup where you can plot the graticule and a crude 
coastline.  From there start with simple operations like +o_lon_0=0 and try a 
few plots with varying +o_lat_0.  Forexample, you'll find that +o_lat_0=45 
will shift the pole halfway between the middle and the top of the plot.  Etc, 

Granted, no coastline for Mars so try things out on Earth first.  ;-)

Jerry and the low riders:Daisy May and Joshua
"The being cannot be termed rational or virtuous,
who obeys any authority, but that of reason."
---Mary Wollstonecraft 1792

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