Re: [postgis-users] polygon with equally spaced points from an existing polygon
On Tue, Mar 12, 2013 at 5:22 AM, Luis Tavares wrote: > Hi, > > How do I create a polygon with equally spaced points from an existing > polygon? > > I know that more the curvature or concavity changes sign more points are > needed. So one solution would be to calculate the minimum of all distances > between two consecutive points in the original polygon and use that distance > to build my polygon with equally spaced points. Is this correct? If so, How > do I proceed from here? Any ready made solution? > What about ST_Simplify? regards p -- Paolo Corti Geospatial software developer web: http://www.paolocorti.net twitter: @capooti skype: capooti ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
Re: [postgis-users] polygon with equally spaced points from an existing polygon
Hi, Try st_segmentize (http://postgis.net/docs/manual-2.0/ST_Segmentize.html) Nicolas On 12 March 2013 09:08, Paolo Corti wrote: > On Tue, Mar 12, 2013 at 5:22 AM, Luis Tavares wrote: > > Hi, > > > > How do I create a polygon with equally spaced points from an existing > > polygon? > > > > I know that more the curvature or concavity changes sign more points are > > needed. So one solution would be to calculate the minimum of all > distances > > between two consecutive points in the original polygon and use that > distance > > to build my polygon with equally spaced points. Is this correct? If so, > How > > do I proceed from here? Any ready made solution? > > > > What about ST_Simplify? > regards > p > > -- > Paolo Corti > Geospatial software developer > web: http://www.paolocorti.net > twitter: @capooti > skype: capooti > ___ > postgis-users mailing list > postgis-users@lists.osgeo.org > http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users > ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
Re: [postgis-users] polygon with equally spaced points from an existing polygon
On Mon, Mar 11, 2013 at 09:22:09PM -0700, Luis Tavares wrote: > How do I create a polygon with equally spaced points from an existing polygon? Looks like a two steps process: 1) drop vertices that are too close (st_simplify may help) 2) add vertices where missing (st_simplify) > I know that more the curvature or concavity changes sign more points are > needed. So one solution would be to calculate the minimum of all distances > between two consecutive points in the original polygon and use that distance > to build my polygon with equally spaced points. Is this correct? If so, How > do I proceed from here? Any ready made solution? Calculating the minimum of all distances between two consecutive points could be a useful standalone function. Don't you also need minimum distance between any two points ? I'm curious about the use case for the "consecutive only" approach. --strk; ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
Re: [postgis-users] polygon with equally spaced points from an existing polygon
Hi all, Thanks for your suggestions, What I really need is a polygon that have exactly the same geometric center (centroid) of the original polygon. I don´t know If generalization algorithms (like st_simplify) have this property. Same for st_segmentize. I need to make some tests first. strk, The use case is precisely calculating the polygon´s centroid by averaging the coordinates of all the points of the polygon. In order to perform this I think I need to have equally spaced points. Note that I´m working on the ellipsoid so st_centroid no good to me...and I don´t want to project coordinates. Thanks Luis Tavares From: Sandro Santilli To: Luis Tavares ; PostGIS Users Discussion Sent: Tuesday, March 12, 2013 8:50 AM Subject: Re: [postgis-users] polygon with equally spaced points from an existing polygon On Mon, Mar 11, 2013 at 09:22:09PM -0700, Luis Tavares wrote: > How do I create a polygon with equally spaced points from an existing polygon? Looks like a two steps process: 1) drop vertices that are too close (st_simplify may help) 2) add vertices where missing (st_simplify) > I know that more the curvature or concavity changes sign more points are > needed. So one solution would be to calculate the minimum of all distances > between two consecutive points in the original polygon and use that distance > to build my polygon with equally spaced points. Is this correct? If so, How > do I proceed from here? Any ready made solution? Calculating the minimum of all distances between two consecutive points could be a useful standalone function. Don't you also need minimum distance between any two points ? I'm curious about the use case for the "consecutive only" approach. --strk;___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
Re: [postgis-users] polygon with equally spaced points from an existing polygon
On Tue, Mar 12, 2013 at 10:16:20AM -0700, Luis Tavares wrote: > The use case is precisely calculating the polygon´s centroid by averaging the > coordinates of all the points of the polygon. In order to perform this I > think I need to have equally spaced points. Note that I´m working on the > ellipsoid so st_centroid no good to me...and I don´t want to project > coordinates. ST_Simplify does indeed work on the cartesian plane, but you don't really need to drop existing vertices for the above computation, do you ? You can use ST_Segmentize(geography) to augment vertices density on the ellipsoid. --strk; http://www.cartodb.com - Map, analyze and build applications with your data ~~ http://strk.keybit.net ___ postgis-users mailing list postgis-users@lists.osgeo.org http://lists.osgeo.org/cgi-bin/mailman/listinfo/postgis-users
