Oblique Parameter Question

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Oblique Parameter Question

Mike Darweesh-2
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


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Oblique Parameter Question

Mike Darweesh-2
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


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Re: Oblique Parameter Question

Mike Darweesh
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


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Re: Re: Oblique Parameter Question

Gerald I. Evenden-2
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,
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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Re: Re: Oblique Parameter Question

Clifford J Mugnier
In reply to this post by Mike Darweesh-2




Mike and Michael,

Since the latest issue (October 2005) of "Photogrammetric Engineering and
Remote Sensing" is entirely devoted to Mars mapping, perhaps you should
seek some help from the list of contributing authors in that particular
issue.  The "Grids and Datums" column in that issue is the first monthly
column that I have not personally written since 1997.  Dr. Randolph L. Kirk
wrote that column as well as he's one of the Guest Editors of the special
issue.

Why not ask him for help?  He certainly knows his stuff.

C. Mugnier
LSU

By the way, using the Platte Caree for Mars will set back the science of
Cartography about 400 years.  Pick something better than that!
--------------------------
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

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