Is anyone working on a set of types and transformations suitable for
geographic coordinates, e.g., to use in mapping or GIS applications?
Do there exist any such types already?  Note that I'm familiar with
the "normal" geometry types, but these are not really suitable for
"real" mapping/GIS applications.

Thanks for any pointers.

Cheers,
Brook


Wed, 16 Aug 2000 07:55:59 -0600 (MDT)
Brook Milligan <brook@biology.nmsu.edu>
geographic coordinate types?

For example?  We use the point type for doing long/lat coordinates, and
for calculating distance between  places on one of our projects ... but I
take it you are thinking of something more elaborate then that?

On Wed, 16 Aug 2000, Brook Milligan wrote:

> Is anyone working on a set of types and transformations suitable for
> geographic coordinates, e.g., to use in mapping or GIS applications?
> Do there exist any such types already?  Note that I'm familiar with
> the "normal" geometry types, but these are not really suitable for
> "real" mapping/GIS applications.
> 
> Thanks for any pointers.
> 
> Cheers,
> Brook
> 

Marc G. Fournier                   ICQ#7615664               IRC Nick: Scrappy
Systems Administrator @ hub.org 
primary: scrappy@hub.org           secondary: scrappy@{freebsd|postgresql}.org 


Wed, 16 Aug 2000 11:10:45 -0300 (ADT)
The Hermit Hacker <scrappy@hub.org>
Re: geographic coordinate types?
   For example?  We use the point type for doing long/lat coordinates, and
   for calculating distance between  places on one of our projects ... but I
   take it you are thinking of something more elaborate then that?

Yes.  I was thinking of a 3D coordinate system and the various
transformations needed to span the globe, take into account
measurement errors, etc.

Cheers,
Brook

Wed, 16 Aug 2000 08:49:02 -0600 (MDT)
Brook Milligan <brook@biology.nmsu.edu>
Re: geographic coordinate types?
The Hermit Hacker wrote:
> 
> For example?  We use the point type for doing long/lat coordinates, and
> for calculating distance between  places on one of our projects ... but I
> take it you are thinking of something more elaborate then that?
> 

i got the impression that the "real" mapping types includes
transformation functions -- i.e., we have data in both state plane and
lat/long (UTM) and they need to play nice together.  some more details
would be nice -- there are free packages out there to do the
transformation at the application level (search for PROJ and gctpc for a
couple of pointers), but nobody i know of has needed anything like that
enough to actually put it in the database itself.  i think it would be
interesting to put out there exactly what you need to see what isn't
there, what can be worked around, what would be a good target for future
development, etc.   i've had a few "wouldn't it be nice thoughts" about
similar things, but it's always been easier to workaround because as far
as i can tell there's not a whole lot of interest in those features. 

-- 

Jeff Hoffmann
PropertyKey.com

Wed, 16 Aug 2000 09:51:02 -0500
Jeff Hoffmann <jeff@propertykey.com>
Re: geographic coordinate types?
There is a group working on a GIS front end to PostgreSQL over at:

	http://fmaps.sourceforge.net/

Also, take a look at:

	http://www.ossim.org/

More information can be found at:

	http://freegis.org/

T.

Brook Milligan wrote:
> 
>    For example?  We use the point type for doing long/lat coordinates, and
>    for calculating distance between  places on one of our projects ... but I
>    take it you are thinking of something more elaborate then that?
> 
> Yes.  I was thinking of a 3D coordinate system and the various
> transformations needed to span the globe, take into account
> measurement errors, etc.
> 
> Cheers,
> Brook

-- 
Timothy H. Keitt
National Center for Ecological Analysis and Synthesis
735 State Street, Suite 300, Santa Barbara, CA 93101
Phone: 805-892-2519, FAX: 805-892-2510
http://www.nceas.ucsb.edu/~keitt/

Wed, 16 Aug 2000 11:23:59 -0700
"Timothy H. Keitt" <keitt@nceas.ucsb.edu>
Re: geographic coordinate types?
It would be quite easy to add functions for projecting into different
coordinate systems using PROJ.4.  The problem is how do you keep track
of the metadata?  The projections take parameters (prime meridian, etc.)
and so it would be up to the user to keep track of which projection they
are using.  (Otherwise you have to define a new data type for all
projection/parameter combinations which doesn't make much sense.)

AFAICT, most GIS programs simply project into a cartesian projection and
then use standard euclidean geometry for queries, i.e., exactly what is
currently supported in postgres (at least in 2D).  For small scale work,
that's probably sufficient.  However, linearity of the coordinate system
will not hold at larger scales. 

At any rate, it would be very nice to have a geographic coordinate type
in postgres.  Once the meaning of certain predicates (greater than,
contains, etc.) are defined, these can be indexed as well.  Add in the
aforementioned projection code and you have a reasonable start on a GIS.

Tim

Jeff Hoffmann wrote:
> 
> i got the impression that the "real" mapping types includes
> transformation functions -- i.e., we have data in both state plane and
> lat/long (UTM) and they need to play nice together.  some more details
> would be nice -- there are free packages out there to do the
> transformation at the application level (search for PROJ and gctpc for a
> couple of pointers), but nobody i know of has needed anything like that
> enough to actually put it in the database itself.  i think it would be
> interesting to put out there exactly what you need to see what isn't
> there, what can be worked around, what would be a good target for future
> development, etc.   i've had a few "wouldn't it be nice thoughts" about
> similar things, but it's always been easier to workaround because as far
> as i can tell there's not a whole lot of interest in those features.
> 

-- 
Timothy H. Keitt
National Center for Ecological Analysis and Synthesis
735 State Street, Suite 300, Santa Barbara, CA 93101
Phone: 805-892-2519, FAX: 805-892-2510
http://www.nceas.ucsb.edu/~keitt/

Wed, 16 Aug 2000 11:45:11 -0700
"Timothy H. Keitt" <keitt@nceas.ucsb.edu>
Re: geographic coordinate types?