[postgis-devel] Triangulation engine and constrainted polygontriangulation

[maplabs at light42.com]

Hi Alexander -

  to respond, I am looking here:

  http://svn.osgeo.org/postgis/branches/2.1
  http://svn.osgeo.org/geos/branches/3.4/

  http://sourceforge.net/projects/jts-topo-suite/files/
 
 
--
  You may know, that PostGIS uses the GEOS library for a lot of the 
computations. GEOS is a C++ port of selected JTS code. 
(there is a second geometry engine in progress, but we wont think about 
that now)
 
  You can see ST_DelaunayTriangles function definition here

    postgis_21_branch/extensions/postgis/sql/postgis.sql  Line 3202

resulting in a working function signature like this:

natural_earth2=# \df st_del*
List of functions
-[ RECORD 1 ]-------+------------------------------------
Schema              | public
Name                | st_delaunaytriangles
Result data type    | geometry
Argument data types | g1 geometry, tolerance double precision DEFAULT 0.0,
                        flags integer DEFAULT 0
Type                | normal

General triangle building and handing in PostGIS:

    postgis_21_branch/liblwgeom/lwtriangle.c

Type enumeration:

    postgis_21_branch/liblwgeom/liblwgeom.h
... 
#define TRIANGLETYPE            14

=========
What does this mean?
   there are several directions to look for answers.. 

The Standards:
  There are formal SQL-MM and SimpleFeatures definitions, which serve as the
relevant guiding standards, towards which PostGIS is written. 

The Geomtry Code Mothership - Java Topology Suite (JTS):
  Another are the exposed JTS routines, as above, which are callable. 

Working Tests:
  Yet another direction for answers is the tests, which are included in the
PostGIS source tree. When new features are added to the project, good practice
is to add tests at the same time. For curious (and practical) people, the
tests are a good place to look for small working examples.. 

  postgis_21_branch/regress/delaunaytriangles.sql
 
  hmm, not so much there.. terse.. a big TODO at the top.. 
 
===============
So, in conclusion, I will infer the following:

  * Triangles in PostGIS are a defined type
  * some really really simple ops are defined in lwgeom
  * real computation on triangle comes from JTS
  * there has not been a lot of embellishment on PostGIS TRIANGLE to date

-------
Brian M Hamlin
OSGeo California Chapter
blog.light42.com

On Sun, 2 Feb 2014 13:44:26 +0100, Alexander Weidauer 
<Weidauer at ifaoe.de> wrote:
Dear List, at the moment I use offline triangulation based on the 
triangle tool of J. Schewchuck 
(http://www.cs.cmu.edu/~quake/triangle.html) to manage, raster 
interplation, fractal indexing, polygon aggragation... . I have seen, 
that PostGIS 2.1 offers triangulation features 
(ST_DelaunayTriangulation) now. 
>
> I have some questions:
>
> 1. Which triangulation engine is used?
> 2. Where can I find it in in the repo how Are the maintainers?
> 3. Triangle has some smart an important features like mesh refinement 
> (sizes and angles of the mesh), and !important constrained polygon 
> triangulation. Are this features accessible in PostGIS 2.1?
>
> Thanks in advance Alexander  Weidauer
>
> -------------------------------------------------------------------------------------------------
> Dipl. Phys. A. Weidauer,  Fachbereich GIS/ EDV
> Tel.: +49 (0) 38204 / 618-13
> mail: weidauer at ifaoe.de
> web: www.ifaoe.de<http://www.ifaoe.de/>
> -------------------------------------------------------------------------------------------------
>
> _
>
> IfAÖ
> Institut für Angewandte Ökosystemforschung GmbH
> Mitglied der GICON® - Gruppe
> Alte Dorfstrasse 11
> 18184 Neu Broderstorf
> GERMANY
>
> Telefon: +49 38204 618-0
> Telefax: +49 38204 618-10
> Geschäftsführung: Prof. Dr.-Ing. habil. Jochen Großmann 
> (geschäftsführender Gesellschafter)
> eingetragen beim Amtsgericht Rostock unter HRB 5324
>
> Diese E-Mail enthält vertrauliche und / oder rechtlich geschützte 
> Informationen. Wenn Sie nicht der richtige Adressat sind oder diese 
> E-Mail irrtümlich erhalten haben, informieren Sie bitte sofort den 
> Absender und vernichten Sie diese Mail. Das unerlaubte Kopieren sowie 
> die unbefugte Weitergabe dieser Mail ist nicht gestattet. 
>
> This e-mail may contain confidential and / or privileged information. 
> If you are not the intended recipient (or have received this e-mail 
> in error) please notify the sender immediately and destroy this 
> e-mail. Any unauthorized copying, disclosure or distribution of the 
> material in this e-mail  is strictly forbidden. 
> _______________________________________________
> postgis-devel mailing list
> postgis-devel at lists.osgeo.org
> http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-devel
>
>