[Proj] Having all projection inverses was Re: Why

Melita Kennedy mkennedy2 at earthlink.net
Wed Oct 29 15:39:45 EDT 2008

>Date: Sun, 26 Oct 2008 13:23:05 -0400
>From: "Gerald I. Evenden" <geraldi.evenden at gmail.com>
>Subject: [Proj] Why?
>To: "PROJ.4 and general Projections Discussions"
>	<proj at lists.maptools.org>
>One burning question has come up in my mind about the need for inverse 
>solutions for non-grid-system projections like Aitoff, Hammer, etc.: why?
>It is easy to understand the need in cadastral work to be able to freely 
>interchange between Cartesian and Geographical space because the source of 
>information is in either system.
>But Aitoff or Winkel Tripel.  What source information is in either projection.  
>Are people now going to digitize NGS maps?  Certainly nobody uses Winkel 
>Tripel for cadastral application---do they?
>Just very curious.

ESRI has worked out inverses for a few projections because a customer 
had put data into them years before and now wanted to use the data 
again. They didn't have the data in any other format. Other techniques, 
like rubbersheeting or transforming the data, just didn't work that 

At least how we used to do it, you also must have an inverse to project imagery 
(once the output cells are defined, unproject to figure out the cell values). 


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