I'm trying to find the easiest way to get the concave polygons. The way of getting them has to be by using PostgreSQL or it has to be a part of C# code, because the user will be able to move a lonlat point from one subarea to another, which means that concave polygons will be generated on demand. I have read all the ideas posted on this thread and I find the alpha shapes quite useful, just need to figure it out how to implement this into my C# code that generates the Google Earth kml files. I'm also quite a beginner in C# programming.<br>
<br>I attached a text file containing points for new polygon and also two pictures, first one with convex polygon and second with concave polygon to see what the output should be.<br><br>Thanks for all your answers!<br><br>
<br><div class="gmail_quote">On Wed, Dec 3, 2008 at 6:46 PM, Martin Davis <span dir="ltr"><<a href="mailto:mbdavis@refractions.net">mbdavis@refractions.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
You might also check out this paper:<br>
<br>
<a href="http://www.foss4g.org/index.php/foss4g/2008/paper/view/226/157" target="_blank">http://www.foss4g.org/index.php/foss4g/2008/paper/view/226/157</a><br>
<br>
It uses a "connect-buffer-simplify" approach. <br><div><div></div><div class="Wj3C7c">
Martin Davis wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
I think the ideas for the solution have already been posted on this thread - you either need to use alpha shapes or one of the concave hull algorithms. It sounded like pgrouting has an alpha shapes implementation - that would probably be the easiest way forward. Implementing the other algorithms would be non-trivial.<br>
<br>
It might also help if you posted a picture of what you think the desired output should be, for the sample data you posted.<br>
<br>
Aleš Kecman wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi!<br>
<br>
I'm still struggling with this "concave hulls" and it seems I just can't find the way how to do it. I'm sending a text file with some longitude and latitude points of selected subarea from which I need to get a concave polygon. There is only one polygon in attached text file. In my database I have around 500 000 points from which I need to form around 700 polygons. If there is a way to do it in PostGis I would really appreciate any help. I also attached a jpg picture of my convexhull polygon. Thanks!!!<br>
<br>
Greets, Ales.<br>
<br>
<br>
<br>
On Mon, Nov 24, 2008 at 12:13 PM, Mark Cave-Ayland <<a href="mailto:mark.cave-ayland@siriusit.co.uk" target="_blank">mark.cave-ayland@siriusit.co.uk</a> <mailto:<a href="mailto:mark.cave-ayland@siriusit.co.uk" target="_blank">mark.cave-ayland@siriusit.co.uk</a>>> wrote:<br>
<br>
Aleš Kecman wrote:<br>
<br>
Hi!<br>
<br>
<br>
I'm new to Postgis and would really like to get some help on<br>
getting a concave hull from an array of points.<br>
<br>
For example:<br>
<br>
I have an array of points - longitude and latitude of<br>
buildings in particular area in the city. I already managed to<br>
get a convex hull polygon from this array of points, but this<br>
is not really helpful. What I'm trying to get is some kind of<br>
concave hull polygon from an array of points, which I would<br>
further like to use in Google Earth kml file.<br>
<br>
Thanks.<br>
<br>
<br>
<br>
Hi Aleš,<br>
<br>
Does ST_Union() help you at all?<br>
<br>
<br>
ATB,<br>
<br>
Mark.<br>
<br>
-- Mark Cave-Ayland<br>
Sirius Corporation - The Open Source Experts<br>
<a href="http://www.siriusit.co.uk" target="_blank">http://www.siriusit.co.uk</a><br>
T: +44 870 608 0063<br>
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