Get the middle line of the River polygon
TamasPiszak
Is it possible in Mapinfo somehow to get the middle line of a poligon
feature?
Thanks in advance
InterRob
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Davidll
would have to buy FME! (you can get a trial version).
The transformer notes include the following if you have any ambitions
to implement something yourself:
The algorithm used to calculate the angular bisector network for the
Medial Axis or Straight Skeleton mode was designed by Petr Felkel and
Stepan Obdrzalek and is provided as-is, with no warranties. The paper
outlining this algorithm is referenced in Straight Skeleton
Implementation, 1998, "SCCG 98: Proceedings of the 14th Spring
Conference on Computer Graphics," pages 210-218, ISBN 80-223-0837-4
(Publisher: Comenius University, Bratislava).
Cheers
David L
Bill Thoen
> There is no easy solution to this. In fact, there is no solid
> definition of a "middle line" of a polygon, either...
>
> Anyway, one approach would be to find a linear trend line (e.g. least
> squares), taking all polygon nodes as a point cloud...
>
> Good luck!
> Rob
>
> 2011/4/27 TamasPiszak <piszak...@gmail.com
>
> Hi group!
> Is it possible in Mapinfo somehow to get the middle line of a poligon
> feature?
>
If you need a "mathematically pure" solution, then this a hard problem,
but I believe a solution is shown in most Computational Geometry books.
If you just need "looks right", then here's a quick trick. This is
easier to show than explain so I've included a small map which should
appear on the right.
This is done using 10-mile buffers. You make a buffer around the
polyline of your polygon, then run Convert to Polylines on the buffer,
then run Disaggregate on the parallel lines and repeat until your
central polylines are essentially linear. It's relatively easy to
program in MapBasic if your Jommetry-fu is decent, because there are a
couple of tough spots.
As you get closer to the center the polylines get more and more linear,
so the final step is to thread your center line through the most
end-point like point in the center ring, and then I added a smoothing
operation to the line.
--
*Bill Thoen*
GISnet - www.gisnet.com
303-786-9961
Bill Thoen
2nd try on the
centerline map.
Javier Valencia
The graphs looks more like middle of the” lake” rather than the “river.” A river contour would look more like this:
Best regards,
Javier Valencia, PE
President
Valencia Technology Group, LLC
14315 S. Twilight Ln.
Suite #14
Olathe, Kansas 66062-4571
913-829-0888 Office
913-915-3137 Cell
913-649-2904 Fax
Visit us at: http://www.vtgonline.com
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TamasPiszak
This project was quite urgent and the length of the river was only
some hundred kilometer, so we just drew it, but the informations you
give was quite interresting.
I will read some paper about it!
Thanks again
On ápr. 29, 05:16, "Javier Valencia" <javier.valen...@vtgonline.com>
wrote:
> river contour would look more like this:
>
>
> Javier Valencia, PE
> President
>
> 14315 S. Twilight Ln.
> Suite #14
> Olathe, Kansas 66062-4571
> 913-829-0888 Office
> 913-915-3137 Cell
> 913-649-2904 Fax
>
> Visit us at: <http://www.vtgonline.com/>http://www.vtgonline.com
> Confidentiality Notice
> This electronic mail (including any attachments) may contain information
> that is privileged, confidential, and/or otherwise protected from disclosure
> to anyone other than its intended recipient(s). Any dissemination or use of
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> _____
>
> Behalf Of Bill Thoen
> Sent: Thursday, April 28, 2011 9:28 PMTo:mapi...@googlegroups.com
> Subject: Re: [MI-L] Get the middle line of the River polygon
>
> --
> Bill Thoen
> GISnet -www.gisnet.com
> 303-786-9961
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>
> 34KMegtekintésNézet
>
> image002.jpg
> 1KMegtekintésNézet
>
> image003.png
> 14KMegtekintésNézet
>
> image004.jpg
> 45KMegtekintésNézet
Gamiz Ribelles, Sergi (Regsa)
Many months ago, I posted the same question and I received two tools: they are still very rough, but they solve enough depending on your scale. I prefer Simple_Region_Center_Line 3.MBX for roads, streams, and similars with 1-10 m wide. They don't work well enough for regions 100 m wide or grater.
- Simple_Region_Center_Line_3.MBX is the third attempt from Tony Pilkington. (I have the source code also, but I don't share it with you without the author's permission)
- Trace region.MBX cames from the author of http://mapbasic.net/ . It works worse
-----Mensaje original-----
De: mapi...@googlegroups.com [mailto:mapi...@googlegroups.com] En nombre de TamasPiszak
Enviado el: miércoles, 27 de abril de 2011 14:40
Para: MapInfo-L
Asunto: [MI-L] Get the middle line of the River polygon
Andy Harfoot
coupled with some MapBasic, to automate the extraction of a centreline
for the majority of the rivers in Scotland from the Ordnance Survey's
MasterMap product, so I can confirm that this approach works quite well.
On a few occasions the algorithm generated strange results that had to
be manually fixed, I suspect these were due to coordinate rounding errors.
Cheers,
Andy
--
Andy Harfoot
GeoData Institute
University of Southampton
Southampton
SO17 1BJ
Tel: +44 (0)23 8059 2719
Fax: +44 (0)23 8059 2849
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