Re: Cartographic Projection Library

[John Caron <caron@xxxxxxxxxxxxxxxx>]

John Caron wrote:
> These things always involve 2 transforms:
>
>  (lat,lon) <-- proj --> (projection plane x,y) <-- affine --> (pixel x,y)
>
> The second is an affine transform that handles zoom and pan, by mapping 
> x,y in meters on the projection plane into your screen space.

I just realized that you probably want to map into data index space; so then the affine transform reduces to a linear transform from (x,y) to (i,j).


> James Gallagher wrote:
>
> James Gallagher wrote:
>
> > On Aug 3, 2006, at 2:06 PM, John Cartwright wrote:
> >
> > > Hello All,
> > >
> > > I presume that the libproj that you're referring to is the proj4
> > > library?  I think that it is actively supported, or at least is being
> > > used by active projects - Mapserver, GDAL, GRASS, POSTGIS, etc.   
> > > Closest
> > > thing I know of for a standard projection library  in the  opensource 
> > > GIS
> > > world.
> > >
> > > There's a mailing list at http://lists.maptools.org/mailman/ 
> > > listinfo/proj
> >
> >
> >
> > I am talking about that library. Where I'm having trouble is knowing  
> > how to apply it to an array of data. I know the lat/lon of the  
> > corners, the projection and the ellipsoid, but it seems that libproj  
> > wants to map into something like 'meters' where I want pixels.  
> > Anyway, if there's a simple explanation or example, that would be  
> > great. In the mean time I'll read over the libproj docs and see what  
> > I can figure out.
> >
> > James
> >
> > > -- john
> > >
> > >
> > >
> > >
> > > John Caron wrote:
> > >
> > > > James Gallagher wrote:
> > > >
> > > > > On Aug 3, 2006, at 11:33 AM, Nathan Potter wrote:
> > > > >
> > > > > > I own the USGS "bible" on map projections. Not a library, but it
> > > > > > has all of the stuff from first principles. I have coded a few and
> > > > > > they work good.
> > > >
> > > >
> > > >
> > > > We have a library of java routines coded mostly from Snyder's book.
> > > > Nathan, if you code something that we dont have, we probably want to
> > > > add it.
> > > >
> > > > > Yes, I have that as well, and it was really simple to use it. But,
> > > > > what I would like is a general library of code that OPeNDAP can
> > > > > adopt  so that we can do two things:
> > > > >
> > > > > 1. Not write (re)projection code ourselves; and
> > > > > 2. Build up knowledge within the group so that we don't each spend
> > > > > time (re)learning the same stuff.
> > > > >
> > > > > This just seems like such a basic problem, it's hard to believe
> > > > > everyone codes these themselves.
> > > > >
> > > > > Maybe I just need to print the libproj docs and spend an evening
> > > > > with  them.
> > > >
> > > >
> > > >
> > > > libproj I think is pretty standard for C libraries, but there may be
> > > > some question about if anyone is supporting it.
> > > >
> > > > The CF standard refers to it, and points to docs at
> > > >
> > > > http://www.remotesensing.org/geotiff/proj_list/
> > > >
> > > >
> > > > > James
> > > > >
> > > > > > N
> > > > > >
> > > > > >
> > > > > > On Aug 3, 2006, at 9:50 AM, James Gallagher wrote:
> > > > > >
> > > > > > > Hi all,
> > > > > > >
> > > > > > > I'm looking for a cartographic projection library. Any
> > > > > > > suggestions? I've looked at libproj, but it's not obvious how to
> > > > > > > get it to work with my application.
> > > > > > >
> > > > > > > Thanks,
> > > > > > > James
> > > > > > > --
> > > > > > > James Gallagher                jgallagher at opendap.org
> > > > > > > OPeNDAP, Inc                   406.723.8663
> > > > > >
> > > > > > ========================================================
> > > > > > Nathan Potter                        The OPeNDAP Project
> > > > > > ndp@xxxxxxxxxxx                       http://opendap.org
> > > > > > 541.752.1852 voice
> > > > >
> > > > > --
> > > > > James Gallagher                jgallagher at opendap.org
> > > > > OPeNDAP, Inc                   406.723.8663
> >
> > --
> > James Gallagher                jgallagher at opendap.org
> > OPeNDAP, Inc                   406.723.8663