[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
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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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