Обсуждение: geographic coordinate types?
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
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
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
For example? We use the point type for doing long/lat coordinates, and for calculating distance between places on oneof 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
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/
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/