[Marble-devel] Projections

[Torsten Rahn]

(Had already replied earlier, but still wanted to get some thoughts added to 
my opinion).

What we had been working towards already was turning Projections into plugins. 
This would be achieved by moving all projection dependent code to be dealt  
with by the (Abstract)Projection class in some generic  way. We are already 
pretty close -- except for some "legacy" vector code that is currently subject 
to be refactored anyways.

On Thursday 25 September 2008 05:48:27 Henry de Valence wrote:
> Right now I am thinking that after I do more work on the UTM projection it
> would be cool/fun/interesting/etc to make another projection, and I was
> wondering whether it would be better to do a Mollweide projection, or a
> Winkel Tripel projection (I think that the math of the w-t projection is a
> bit more complicated, but it shouldn't be too hard...)

If it's intended to be shipped with Marble by default I think that Winkel III 
would be the best choice among its kind.  Wikipedia says about it:

"Goldberg & Gott show that the Winkel-Tripel is arguably the best overall 
whole-earth map projection known, producing very small distance errors, small 
combinations of ellipticity and area errors, and the smallest skewness of any 
map. [2]
In 1998, the Winkel Tripel projection replaced the Robinson projection as the 
standard projection for world maps made by the National Geographic Society. 
Many educational institutes and textbooks followed National Geographic's 
example in adopting the projection, and most of those still use it."
Admittedly I personally find it visually most pleasing but of course that just 
comes as a bonus ;-) .
> Or would making more projections not be a good idea?
Well, it really depends. I personally think that we should stick to Marble's 
Manifesto:

http://websvn.kde.org/trunk/KDE/kdeedu/marble/MANIFESTO.txt?revision=676415&view=markup

Hence we should try to stick to a small set of carefully selected projections 
that get shipped by default.

Of course I think that it would be a great thing if somebody would at some 
point create some application that is more focussed on "real" GIS stuff based 
on the MarbleWidget which would target more advanced users. This application 
(let's call it "Cartographer") would then have a different focus in terms of 
user base. Cartographer would have lots of additional options to tinker with 
and maybe powerful ways to deal with the map (and of course it could certainly 
have more dependencies like e.g. gdal or proj4).

But for the MarbleWidget and the Edu-Application I want to ensure a simple 
interface without much dependencies and without stuff that is just relevant for 
experts (and preferably an API that can be understood by non-GIS people).
 
Concerning the UTM projection: I personally don't think that the UTM 
projection as a visual representation should be part of the default 
distribution. 
But I do think that the ability to have points described in the UTM coordinate 
system would certainly be a great thing to have.

Best Regards,

Torsten







>
> Henry
> _______________________________________________
> Marble-devel mailing list
> Marble-devel at kde.org
> https://mail.kde.org/mailman/listinfo/marble-devel