[Gvsig_english] Fwd: PostGis + 3D extension
Jordi Torres
jtorresfabra at gmail.com
Wed Jan 19 18:49:19 CET 2011
Hi Ben,
The problem is that the roots of GIS are in digital cartography,
> which is a 2D discipline. So the GIS datamodels were all originally
> designed for 2D, including the vector model. Raster elevation
> layers served the purpose as simple pseudo-3D models ("2.5 D").
>
> As far as I can tell in the 2.0 branch we will have support for 3D
geometries according to the GML ISO specification. We will be capable of
defining solids, etc.
> As time went by, more and more people from "3D fields", such as
> geology created a demand for real 3D data management, so capabilities
> to load, view, and (to a limited degree) add 3D data was introduced.
> And some GIS (such as GRASS GIS) also learned a limited amount of
> 3D analysis.
>
> But many fundamental GIS aspects, such as topology, remain firmly
> in the 2D domain, and it will be a long time before that changes,
> because 3D topological relationships are a whole lot more complex
> than 2D ones. Currently, 3D remains an "add-on" to GIS, that works
> more or less well (and then there is 4D, but let's not even get
> into that).
>
>
I'm agree, and in my opinion, the vast majority of 3D users mainly to give a
different perspective of the data for a visual analysis. This is changing,
and in the near future 3D geoprocesses (like multiresolution algorithms for
massive data) will be absolutelly necessary.
> Polygons versus more complex 3D shapes are a good example. By
> definition a polygon is a planar construct. Anything more complex than
> that must be sub-divided into simpler polygons (usually 3D triangles),
> so the GIS vector model can handle them. E.g. a TIN is just a collection
> of simple triangles. And any other shape can also be decomposed into
> triangular "faces".
>
For the records, gvSIG3D don't support TIN at the moment.
> -- And I don't think the gvSIG 3D extension handles voxels yet (?)
>
Are you kidding me? ;).
Cheers!
>
> ----- Original Message -----
> > Yes, you are right.
> >
> > What it is about is how to handle "dirty" polygons that is invalid.
> > How to find that they are invalid without putting to much effort in
> > it.
> >
> > The isValid function is a GEOS-function and only handles x z
> > coordinates as far as I know, so a part of extending PostGIS
> > capabilities in 3D is
> > taking care of validation. Those functions is not in place yet (I
> > think, I have if something new has been committed there by the guy
> > implementing TIN and Polyhedralsurface)
> >
> > Do you have a good way of validating that the polygon is coplanar in
> > gvSIG, I guess you have to handle invalid data too. How do you
> > validate the data?
> >
> > Or same question from another angle. How do you define the plane in 3D
> > extension?
> >
> > Or what happens if the extension gets the polygon I had as example?
> > I will try when I get it up running :-)
> >
> > I am a novice in 3D so sorry for maybe naive questions.
> >
> >
> > Regards
> > Nicklas
> >
> >
> >
> >
> >
> > On Wed, 2011-01-19 at 16:03 +0100, Jordi Torres wrote:
> > > I missed the link... :S
> > >
> > > [1]http://postgis.refractions.net/docs/ch04.html
> > >
> > >
> > > 2011/1/19 Jordi Torres <jtorresfabra at gmail.com>
> > > Hi Nicklas,
> > >
> > > What I meant is that a polygon is a two-dimensional shape,
> > > enclosing an area with its vertices that is in the same
> > > plane, coplanar. If you don't define your polygons this way
> > > it's impossible to know how to tesellate and render it. I
> > > don't know about the specification of polygons in postgis,
> > > but maybe
> > > it's up to the user to define its vertices correctly. I
> > > found this[1] in the postgis doc, see point 4.3.5, maybe it
> > > helps.
> > >
> > > Greetz.
> > >
> > > [1]
> > >
> > >
> > > 2011/1/19 Nicklas Avén <nicklas.aven at jordogskog.no>
> > > sorry about off list posting
> > >
> > >
> > >
> > >
> > > On Wed, 2011-01-19 at 14:35 +0100, Jordi Torres
> > > wrote:
> > > > Hi Nicklas,
> > > >
> > > > Please, let' s take this conversation "on-list".
> > > > The
> > > attacments did
> > > > not pass the list control, that's the reason why I
> > > wrote to you
> > > > directly. About generating 3D datasets it's simple
> > > > if you have
> > > the data in .shp
> > > > (using shp2pgsql). That's the way I get my data.
> > > > In the other hand, a polygon cannot be in more
> > > > than
> > > one plane in 3D,
> > > > if this is the case, this structure must be
> > > tessellated into triangles
> > > > or at least polygons in the same plane.
> > >
> > >
> > > Well, what do you mean by cannot be in more than one
> > > plan?
> > >
> > > I understand that it cot can when it comes to
> > > rendering and so on.
> > > And it cannot when it comes to valid polygons.
> > >
> > > But you can express a polygon in wkt that has
> > > vertexpoints in more than
> > > one plan.
> > >
> > > for example:
> > > POLYGON((0 0 0,0 5 0, 0 5 5, 10 5 5, 10 5 0, 10 0 0,
> > > 0 0 0))
> > >
> > > In many examples the result is undefined and
> > > impossible to decide
> > > without more information and that's why I have to
> > > deal with it in
> > > distance calculations and send an error msg instead
> > > of trying to
> > > calculate the distance.
> > >
> > > Or am I missing something?
> > >
> > > Regards
> > > Nicklas
> > >
> > >
> > >
> > >
> > >
> > > > (the same as openGL do when rendering concave
> > > polygons). May be the
> > > > tesselator included in the 3D extension eats this
> > > kind of structure,
> > > > but I don't trust.
> > > >
> > > > About PostGis I am a noob or less than a noob. I
> > > only know the basics
> > > > to set a database and do a sql query. And I
> > > > learned
> > > it yesterday :). I
> > > > am a 3D developer, and postgis is a tangential
> > > theme for me. So for
> > > > the questions about postGIS ask to the gurus in
> > > > the
> > > list... ;)
> > > >
> > > > Cheers.
> > > >
> > > >
> > > > 2011/1/19 Nicklas Avén
> > > > <nicklas.aven at jordogskog.no>
> > > > Yes, that would be nice :-)
> > > >
> > > > It is a little bit difficult to create 3D
> > > datasets I think, at
> > > > least if
> > > > the polygons contains more than 3 points
> > > (counting the first
> > > > and last as
> > > > 1) because they have to be in the same
> > > > plan.
> > > That is the part
> > > > in the 3D
> > > > distance code that I am most worried
> > > > about.
> > > Now there is no
> > > > real test if
> > > > people sends polygons not on one single
> > > > plan
> > > to the function,
> > > > because such a test is quite expensive to
> > > > calculate
> > > if the polygon has
> > > > many points. Also there have to be some
> > > tolerance.
> > > >
> > > > Have you tried the PostGIS trunk lately?
> > > >
> > > > It will be interesting to test and
> > > > visualize st_3d_shortestline through
> > > > gvSIG.
> > > >
> > > > Cheers
> > > > Nicklas
> > > >
> > > >
> > > > On Wed, 2011-01-19 at 13:55 +0100, Jordi
> > > Torres wrote:
> > > > > Hi Nick,
> > > > >
> > > > > Is a lot of triangular separate
> > > > > polygons,
> > > if you want the
> > > > archive to
> > > > > do testing I can send it to you.
> > > > >
> > > > > Cheers.
> > > > >
> > > > > 2011/1/19 Nicklas Avén
> > > <nicklas.aven at jordogskog.no>
> > > > > Thanks a lot
> > > > >
> > > > > I will try it as soon as
> > > > > possible.
> > > When I have this
> > > > woking
> > > > > there will be
> > > > > a blog post about this extension
> > > and comming 3d
> > > > distance
> > > > > functions in
> > > > > postgis.
> > > > >
> > > > > Is TIN supported? or is it a lot
> > > of triangular
> > > > separate
> > > > > polygons in the
> > > > > example picture?
> > > > >
> > > > > Great work!
> > > > > Thanks
> > > > >
> > > > > /Nicklas
> > > > >
> > > > >
> > > > >
> > > > > On Wed, 2011-01-19 at 13:47
> > > > > +0100,
> > > Jordi Torres
> > > > wrote:
> > > > > >
> > > > > >
> > > > > > ---------- Forwarded message
> > > ----------
> > > > > > From: Jordi Torres
> > > <jtorresfabra at gmail.com>
> > > > > > Date: 2011/1/19
> > > > > > Subject: Re: [Gvsig_english]
> > > PostGis + 3D
> > > > extension
> > > > > > To: Users and Developers
> > > > > > mailing
> > > list
> > > > > >
> > > <gvsig_internacional at listserv.gva.es>
> > > > > >
> > > > > >
> > > > > > Hi Nicklas,
> > > > > >
> > > > > > Here you have attached a zip
> > > file. Substitute the
> > > > jars in
> > > > > the way Fran
> > > > > > told to you.
> > > > > >
> > > > > > And congrats to jaspa teams!!
> > > Good work!
> > > > > >
> > > > > > Cheers.
> > > > > >
> > > > > > 2011/1/19 Francisco José
> > > Peñarrubia
> > > > <fpenarru at gmail.com>
> > > > > >
> > > > > >
> > > > > > Hi.
> > > > > >
> > > > > > I just want to remark
> > > and say thanks to
> > > > JASPA team,
> > > > > who did
> > > > > > the hard work of this
> > > patch in gvSIG
> > > > Sprint. I hope
> > > > > we can use
> > > > > > it in 1.11 release.
> > > > > >
> > > > > >
> > > http://jaspa.forge.osor.eu/
> > > > > >
> > > > > > Best regards.
> > > > > >
> > > > > > Jordi, please, can you
> > > send the latest
> > > > jars to
> > > > > Niklas?. I will
> > > > > > create a patch and
> > > upload it to the
> > > > repository.
> > > > > >
> > > > > > El 19/01/2011 13:30,
> > > Jordi Torres
> > > > escribió:
> > > > > > >
> > > > > > > Hi Nick and Fran,
> > > > > > >
> > > > > > > I have started a new
> > > thread in the list,
> > > > this way
> > > > > we won't
> > > > > > > merge topics.
> > > > > > >
> > > > > > > Fran has fixed the
> > > issues and now we are
> > > > able to
> > > > > see 3D
> > > > > > > geometries using
> > > postigs (attached is a
> > > > screenshot
> > > > > of a 3D
> > > > > > > polygons layer). By
> > > the way, polyhedral
> > > > is not
> > > > > supported by
> > > > > > > gvSIG postGis driver
> > > (even I don't now
> > > > if it is
> > > > > OGC
> > > > > > > compliant), so you
> > > have to decompose it
> > > > in
> > > > > polygons.
> > > > > > >
> > > > > > > Cheers!
> > > > > > >
> > > > > > > -- Jordi Torres
> > > > > > > Fabra
> > > > > > >
> > > > > > > gvSIG 3D blog
> > > > > > >
> > > http://gvsig3d.blogspot.com
> > > > > > > Instituto de
> > > Automática e Informática
> > > > Industrial
> > > > > > > http://www.ai2.upv.es
> > > > > > >
> > > > > > >
> > > > > > >
> > > >
> > > _______________________________________________
> > > > > > > Gvsig_internacional
> > > mailing list
> > > > > > >
> > > Gvsig_internacional at listserv.gva.es
> > > > > > >
> > > > >
> > > >
> > >
> http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional
> > > > > >
> > > > > > -- Fran Peñarrubia
> > > > > > Scolab www.scolab.es
> > > > > >
> > > > > > Asociación gvSIG
> > > > > > www.gvsig.com
> > > > > >
> > > > > >
> > > >
> > > _______________________________________________
> > > > > > Gvsig_internacional
> > > mailing list
> > > > > >
> > > Gvsig_internacional at listserv.gva.es
> > > > > >
> > > > >
> > > >
> > >
> http://listserv.gva.es/cgi-bin/mailman/listinfo/gvsig_internacional
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > -- Jordi Torres Fabra
> > > > > >
> > > > > > gvSIG 3D blog
> > > > > > http://gvsig3d.blogspot.com
> > > > > > Instituto de Automática e
> > > Informática Industrial
> > > > > > http://www.ai2.upv.es
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > -- Jordi Torres Fabra
> > > > > >
> > > > > > gvSIG 3D blog
> > > > > > http://gvsig3d.blogspot.com
> > > > > > Instituto de Automática e
> > > Informática Industrial
> > > > > > http://www.ai2.upv.es
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > > -- Jordi Torres Fabra
> > > > >
> > > > > gvSIG 3D blog
> > > > > http://gvsig3d.blogspot.com Instituto de
> > > > > Automática e Informática
> > > Industrial
> > > > > http://www.ai2.upv.es
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > -- Jordi Torres Fabra
> > > >
> > > > gvSIG 3D blog
> > > > http://gvsig3d.blogspot.com Instituto de
> > > > Automática e Informática Industrial
> > > > http://www.ai2.upv.es
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > --
> > >
> > > Jordi Torres Fabra
> > >
> > > gvSIG 3D blog
> > > http://gvsig3d.blogspot.com Instituto de Automática e
> > > Informática Industrial
> > > http://www.ai2.upv.es
> > >
> > >
> > >
> > >
> > > -- Jordi Torres Fabra
> > >
> > > gvSIG 3D blog
> > > http://gvsig3d.blogspot.com Instituto de Automática e Informática
> > > Industrial
> > > http://www.ai2.upv.es
> > > _______________________________________________ Gvsig_internacional
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> > > Gvsig_internacional at listserv.gva.es
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> >
> >
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--
Jordi Torres Fabra
gvSIG 3D blog
http://gvsig3d.blogspot.com
Instituto de Automática e Informática Industrial
http://www.ai2.upv.es
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