[postgis-users] Concave hull problem & delaunay triangulation - help needed please
Hi, I'm trying to come up with an approach using Postgis to come up with a polygon representing the outer bounds of a set of points, ie: a polygon passing through all the outer points. Much useful info (as usual - thanks guys!!) at spatialdbadvisor & bostongis but my limited understanding is stalling progress for now. I came across the ST_Concavehull() function, which fails. Indeed, I was surprised to see this actually expands the polygon extent representing the point set, as shown at: http://www.bostongis.com/postgis_concavehull.snippet as this buffers the points in some cases, and often gives quite unexpected (to me anyway) results. Looking for something that fits better, using existing capabilities, I figured I could pretty easily use Delaunay triangulation to create the outer hull, then realised this bridges every second outer point (pretty much by definition). That's easy, just remove any triangles from the polygon where they share a line segment with the polygon. I like Postgis!! I have Simon's code working fine, at least using his example invocation, from: http://www.spatialdbadvisor.com/postgis_tips_tricks/290/r-based-delaunay-triangulation-function-for-postgis-using-the-deldir-package But I can't figure out how to make it work with my point data. I don't know R or PL/R well enough to adapt it. I have a set of sample points in a table: Column | Type | +-+- id | integer | not null default geom | geometry(Point) | Can anyone explain, ideally in words of one syllable or less, how Simon's function from the link above needs to be adapted to read my points dataset as input? Once I get the triangles as an output set I can use Postgis for the rest... Thanks, Brent Wood ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Concave hull problem & delaunay triangulation -help needed please
Brent, Is your data 2D or 3D? You might want to try out the new ST_DelaunayTriangles in 2.1 http://www.postgis.org/documentation/manual-svn/ST_DelaunayTriangles.html Right now I beleive it's just 2D, but work is going on in GEOS land to make it 3D.: http://trac.osgeo.org/geos/ticket/570 It does require upgrading your system to 2.1 development and Geos 3.4.0 dev so might not be an option for you yet. We also have windows build bot builds for those on windows who want to try which gets built whenever there is a change in the 2.1 code base http://www.postgis.org/download/windows/experimental.php (for 9.2 both 32-bit/64-bit and for 9.0,9.1 just 64-bit windows) Hope that helps, Regina http://www.postgis.us _ From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users-boun...@postgis.refractions.net] On Behalf Of pcr...@pcreso.com Sent: Friday, August 31, 2012 11:42 PM To: PostGIS Users Discussion Subject: [postgis-users] Concave hull problem & delaunay triangulation -help needed please Hi, I'm trying to come up with an approach using Postgis to come up with a polygon representing the outer bounds of a set of points, ie: a polygon passing through all the outer points. Much useful info (as usual - thanks guys!!) at spatialdbadvisor & bostongis but my limited understanding is stalling progress for now. I came across the ST_Concavehull() function, which fails. Indeed, I was surprised to see this actually expands the polygon extent representing the point set, as shown at: http://www.bostongis.com/postgis_concavehull.snippet as this buffers the points in some cases, and often gives quite unexpected (to me anyway) results. Looking for something that fits better, using existing capabilities, I figured I could pretty easily use Delaunay triangulation to create the outer hull, then realised this bridges every second outer point (pretty much by definition). That's easy, just remove any triangles from the polygon where they share a line segment with the polygon. I like Postgis!! I have Simon's code working fine, at least using his example invocation, from: http://www.spatialdbadvisor.com/postgis_tips_tricks/290/r-based-delaunay-tri angulation-function-for-postgis-using-the-deldir-package But I can't figure out how to make it work with my point data. I don't know R or PL/R well enough to adapt it. I have a set of sample points in a table: Column | Type | +-+- id | integer | not null default geom | geometry(Point) | Can anyone explain, ideally in words of one syllable or less, how Simon's function from the link above needs to be adapted to read my points dataset as input? Once I get the triangles as an output set I can use Postgis for the rest... Thanks, Brent Wood ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Concave hull problem & delaunay triangulation -help needed please
Thanks, All things come to those who wait :-) My data is 2D at present... If I can't get thr PL/R solution working I think I'm better off waiting for GEOS 3.4/Postgis 2.1 Cheers, Brent --- On Sat, 9/1/12, Paragon Corporation wrote: From: Paragon Corporation Subject: Re: [postgis-users] Concave hull problem & delaunay triangulation -help needed please To: "'PostGIS Users Discussion'" Date: Saturday, September 1, 2012, 4:48 PM Brent, Is your data 2D or 3D? You might want to try out the new ST_DelaunayTriangles in 2.1 http://www.postgis.org/documentation/manual-svn/ST_DelaunayTriangles.html Right now I beleive it's just 2D, but work is going on in GEOS land to make it 3D.: http://trac.osgeo.org/geos/ticket/570 It does require upgrading your system to 2.1 development and Geos 3.4.0 dev so might not be an option for you yet. We also have windows build bot builds for those on windows who want to try which gets built whenever there is a change in the 2.1 code base http://www.postgis.org/download/windows/experimental.php (for 9.2 both 32-bit/64-bit and for 9.0,9.1 just 64-bit windows) Hope that helps, Regina http://www.postgis.us From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users-boun...@postgis.refractions.net] On Behalf Of pcr...@pcreso.com Sent: Friday, August 31, 2012 11:42 PM To: PostGIS Users Discussion Subject: [postgis-users] Concave hull problem & delaunay triangulation -help needed please Hi, I'm trying to come up with an approach using Postgis to come up with a polygon representing the outer bounds of a set of points, ie: a polygon passing through all the outer points. Much useful info (as usual - thanks guys!!) at spatialdbadvisor & bostongis but my limited understanding is stalling progress for now. I came across the ST_Concavehull() function, which fails. Indeed, I was surprised to see this actually expands the polygon extent representing the point set, as shown at: http://www.bostongis.com/postgis_concavehull.snippet as this buffers the points in some cases, and often gives quite unexpected (to me anyway) results. Looking for something that fits better, using existing capabilities, I figured I could pretty easily use Delaunay triangulation to create the outer hull, then realised this bridges every second outer point (pretty much by definition). That's easy, just remove any triangles from the polygon where they share a line segment with the polygon. I like Postgis!! I have Simon's code working fine, at least using his example invocation, from: http://www.spatialdbadvisor.com/postgis_tips_tricks/290/r-based-delaunay-triangulation-function-for-postgis-using-the-deldir-package But I can't figure out how to make it work with my point data. I don't know R or PL/R well enough to adapt it. I have a set of sample points in a table: Column | Type | +-+- id | integer | not null default geom | geometry(Point) | Can anyone explain, ideally in words of one syllable or less, how Simon's function from the link above needs to be adapted to read my points dataset as input? Once I get the triangles as an output set I can use Postgis for the rest... Thanks, Brent Wood -Inline Attachment Follows- ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Concave hull problem & delaunay triangulation - help needed please
Brent,I have Simon's code working fine, at least using his example invocation, from:http://www.spatialdbadvisor.com/postgis_tips_tricks/290/r-based-delaunay-triangulation-function-for-postgis-using-the-deldir-packageBut I can't figure out how to make it work with my point data. I don't know R or PL/R well enough to adapt it.I have a set of sample points in a table: Column | Type | +-+- id | integer | not null default geom | geometry(Point) | Can anyone explain, ideally in words of one syllable or less, how Simon's function from the link above needs to be adapted to read my points dataset as input?Try something like this:Once I get the triangles as an output set I can use Postgis for the rest...Thanks, Brent Wood-- Holder of "2011 Oracle Spatial Excellence Award for Education and Research."SpatialDB Advice and Design, Solutions Architecture and Programming,Oracle Database 10g Administrator Certified Associate; Oracle Database 10g SQL Certified ProfessionalOracle Spatial, SQL Server, PostGIS, MySQL, ArcSDE, Manifold GIS, FME, Radius Topology and Studio Specialist.39 Cliff View Drive, Allens Rivulet, 7150, Tasmania, Australia.Website: www.spatialdbadvisor.com Email: si...@spatialdbadvisor.com Voice: +61 362 396397Mobile: +61 418 396391Skype: sggreenerLongitude: 147.20515 (147° 12' 18" E)Latitude: -43.01530 (43° 00' 55" S)GeoHash: r22em9r98wgNAC:W80CK 7SWP3___ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
Re: [postgis-users] Concave hull problem & delaunay triangulation - help needed please
Brent,I have Simon's code working fine, at least using his example invocation, from:http://www.spatialdbadvisor.com/postgis_tips_tricks/290/r-based-delaunay-triangulation-function-for-postgis-using-the-deldir-packageBut I can't figure out how to make it work with my point data. I don't know R or PL/R well enough to adapt it.I have a set of sample points in a table: Column | Type
| +-+- id | integer | not null default geom | geometry(Point) | Can anyone explain, ideally in words of one syllable or less, how Simon's function from the link above needs to be adapted to read my points dataset as input?Just pass in a valid SQL statement that exposes your x y and z point values eg:SELECT ST_Delaunay_Triangles('select ST_X(p.geom) as x,ST_Y(p.geom) as y,ST_Z(p.geom) from sample_points_in_table p') as triangle;regardsSimon-- Holder of "2011 Oracle Spatial Excellence Award for Education and Research."SpatialDB Advice and Design, Solutions Architecture and Programming,Oracle Database 10g Administrator Certified Associate; Oracle Database 10g SQL Certified ProfessionalOracle Spatial, SQL Server, PostGIS, MySQL, ArcSDE, Manifold GIS, FME, Radius Topology and Studio Specialist.39 Cliff View Drive, Allens Rivulet, 7150, Tasmania, Australia.Website: www.spatialdbadvisor.com Email: si...@spatialdbadvisor.com Voice: +61 362 396397Mobile: +61 418 396391Skype: sggreenerLongitude: 147.20515 (147° 12' 18" E)Latitude: -43.01530 (43° 00' 55" S)GeoHash: r22em9r98wgNAC:W80CK 7SWP3___
postgis-users mailing list
postgis-users@postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users
