Little sphere projection

classic Classic list List threaded Threaded
2 messages Options
Reply | Threaded
Open this post in threaded view
|

Little sphere projection

carlob
Thank you for the idea of the radar, that's the image I have in my
mind. But I'm not able to find the proper parameters for proj.
That projection seems to be the same that Snyder calls "Oblique
Azimuthal Equidistant", but I cannot find any
non-cylindrical/non-conic Equidistant projection in proj. Could the
spherical be a special case of conic projection? Should the "ob_tran"
(General Oblique Transformation) be used in this case?
I think this could make things even more difficult to handle.

-- Clifford J Mugnier cjmce at lsu.edu  on Sun Aug 7 21:49:59 EST 2011 wrote:

> For any individual Abbey, the azimuthal equidistant projection (originally
> invented by the monk, Postel) might do in either a spherical or an
> ellipsoidal case.  This projection is identical to what is viewed on a
> radar screen.  The French Hatt projection is one variant used for
> hydrographic projections of harbor surveys in the 19th and early 20th
> centuries.
>
> Clifford J. Mugnier, C.P., C.M.S.
> Chief of Geodesy,
> Center for GeoInformatics
> Department of Civil Engineering
> Patrick F. Taylor Hall 3531
> LOUISIANA STATE UNIVERSITY
> Baton Rouge, LA  70803
[...]
_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj
Reply | Threaded
Open this post in threaded view
|

Re: Little sphere projection

support.mn
Hello,

I am not sure, but it does not sound that your problem is projection
related since in small scale changing the projection does not add
anything too much to the result since almost all normal projections
give similar results when the curvature of the earth does not affect
very much the end result compared to the planar representation of
it?

The projection starts to play role for example near poles when you
are using for example Mercator projection. The distortion of the
plane representation of the earth is so huge that the projection is
no more usable and it gives wrong results. But in most normal
cases where maps are made with fair accuracy there should not
be any need to change the original projection.

You can draw spheres or what ever on all normal maps using
normal local projections and the results should be rather accurate.

Regards: Janne.

------------------------------------------------------

"Carlo A. Bertelli (Charta s.r.l.)" [[hidden email]] kirjoitti:

> Hello,
> I'm trying a simplistic approach to a topological representation. I'm
> mapping the possessions belonging to a group of abbeys in a regional
> space. Il works well at a small scale, but when the abbeys are
> clustered in major towns, the representation ties properties to the
> cluster and not to the single abbey. The fact is that towns (and
> clustering) play a significant role in this story (yes this happens in
> the 18th century), asks for a better representation.
> My idea is analysing each town cluster using a little sphere (or
> ellipsoid) centered on the town whith an emisphere that only covers
> the space of the region, so to show larger distances in town (so to
> distinguish any abbey) and reduced distances far from the town center.
> I think it should not be impossible to craft ad hoc projections, but I
> have no idea on how to do it. Could someone help me?
> TIA
> c
> _______________________________________________
> Proj mailing list
> [hidden email]
> http://lists.maptools.org/mailman/listinfo/proj
>

_______________________________________________
Proj mailing list
[hidden email]
http://lists.maptools.org/mailman/listinfo/proj