Thiessen polygons/voronoi diagram

[neilyj666]

Any aware if these can be created in map? I can only find 6 year old posts about this so I guess there is no great demand!!

[Cecilia.Fantini]

Unfortunately, AutoCAD Map 3D (or Civil 3D) don't have native support for Thiessen/Veronoi polygon analysis.
This has been logged with our development team as a wished enhancement for future releases. However, as you said there is no great demand for this functionality.

The only thing I can suggest is to search on the Internet for existing applications that can do this like for example the OpenSource applications QGIS - www.qgis.org  (with the "ftools" plugin - www.ftools.ca) or GRASS (http://grass.osgeo.org/).

Hope this helps.

Cecilia

[neilyj666]

Thanks for the reply.

It remains a bit disappointing though that Map 3D doesn't support this functionality and the user needs to go to 3rd party tools. If the 3rd party tools provide the functionality, then there must surely be a demand??

It isn't rocket science to produce these diagrams but it is very tedious to produce them manually.....

[Cecilia.Fantini]

Thank you for your feedback.
I fully understand your point and I have forwarded your comments about the importance of this missing functionality to the product development team.
If you want, you can also use the Product Feedback page at http://usa.autodesk.com/adsk/servlet/index?siteID=123112&id=1109794 for providing further comments about any improvements you would like to see within our products.

Thank you.
Kind Regards,

Cecilia

[neilyj666]

Ok - thanks for this

[Murph_Map]

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@neilyj666 wrote:

Ok - thanks for this

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I see you submitting a few "feedback" now that you have a link to that site.  🙂

Good luck.

[neilyj666]

Indeed - also submitted "feedback" about the dreadful retrograde transparency selection in 2012 but I don't expect a solution any time soon......

[phmurphy]

I have been waiting for a long time for the Thiessen polygons.  I have used the free package called R, and even the old old ARcView 3.2 could do this.  Map is in last place in the race to get this done.  It is a valuable tool for all kinds of natural resource issues as well as things like radio tower placement.  I wish Autodesk would put some money into getting this done.

Pat

[gluckett]

There is a free GIS package called qGIS (or Quantum GIS)  - I use it for items like this.  You may want to dump out your data from Map 3D as SHP files (or raster) before you use it.  I have it running on both Windows 7 and my Mac Book.  

It's part of the osgeo.org suite of open source products (that also includes MapGuide).

qGIS has items such as Delauney triangulation and Veronoi polygons (among tons of other items).  Once you have done your analysis, just drag and drop the SHP files back into Map 3D.

gordon

[phmurphy]

Thanks for the source, I will get it for future reference.

Pat

[TerryDotson]

This has been added to DotSoft's MapWorks add-on package.  Simply select points (or inserts) and the exterior boundary to generate the interior linework with no overlaps (as shown) or a collection of closed polygons.

[tcorey]

@TerryDotson @neilyj666 What's the practical application of Theissen polygons? Who would use and how?

[TerryDotson]

From the user who requested this (not long ago) ...

"Civil engineering uses this for giving a real weighting to raingage locations and soil boring locations."

[ChicagoLooper]

@tcorey Great question.

I'm sure there are many examples that could be used to illustrate the usefulness of a Thiessen Polygon, here's an example. (You may ignore the orange boundary, cross hatch patterns and fills, the relevant objects in the image are the yellow monitoring wells and the blue polygons.)

In the image below,  soil samples were taken before monitoring wells MW-03, MW-04 and MW-07 were installed. The samples were sent to the lab for analysis and the results came back with 'hits' indicating the presence of PCE, or tetracholorethene, a solvent common used in dry cleaning.

Note: The use of PCE, a known carcinogen, is subject to regulation established by the EPA. Back in the 80's and earlier, PCE was not subjected to the regulations in place today, so contamination of groundwater and soil at current and former dry cleaning sites was more prevalent than today. Just think, within our lifetime, environmental regs, such as those set by the EPA have changed. Some have become more stringent while others, such as those related to emissions, have been, or have been proposed to be, rolled back or relaxed by the current WH administration, making it easier for industry to operate. It begs the question, ''What is the balance between environmental preservation and industrial growth? Or the balance between health and profits?

We already know we can (using AutoCAD of course) generate an ASCII file such as a csv file, with x,y coordinates for the MWs. If we add a third column to the csv, such as a z-column, we can, with a Thiessen polygonal function generate Thiessen polygons. Unfortunately, Autodesk doesn't have this function. (It's prbably just just an algorithm.)

The z-value, in this case would not be elevation, it would be the PCE 'hit' or the value detected in the soil in parts per million, detected using an 'acceptable testing standard' likely expressed as mg/kg. When the x, y and z's are fed into the Thiessen Function, the polygons are generated. Just three columns of data=Thiessen polygons.

Based on the image above, when standing at the intersection of the blue lines highlighted with the red circle, you could say, the groundwater is equally influenced by the contaminants detected at MW-01, MW-04 and MW-07.

[neilyj666]

@tcorey following on from the excellent explanation from @ChicagoLooper if you assumed these locations were rain gauge locations  then it is possible to use a similar analysis to determine the catchment area based on the rain gauge locations which can be used in hydrological analysis. The Theissen polygon calculation is found in GIS software e.g. ESRI and the free QGIS.

Boreholes are usually located with spacings in the 10's of meters while rain gauges are 10's of kilometers so  this is a useful technique. 

[ChicagoLooper]

If you are installing catch basins then it sounds like the C3D tools named catchment area and water drop analysis on your surface might be better suited to your needs. Rain gauges will indicate water volume while surface analysis (in terms of area and water flow) would indicate drainage polygons and low points.

[fcernst]

Actually that's not the case... The whole idea of Thiessen analysis is to give areal weighting to each data point location to determine a weighted average value for the data within the overall Thiessen polygonal network.

You don't have a true Thiessen polygonal network setup here yet..but just using your shapes for discussion you can see that the data value for MW-03 will be given the most weight (influence) by area, than the other data points in the network.

[Peter2_1]

additional hint: also "The Swamp" has discussions (and solutions?) relating Voronoi:

http://www.theswamp.org/index.php?topic=45126.msg503301#msg503301

Maybe it's helpful.

[ouoba_solaireau]

Hello,

I need help: I want to use the Theissen polygon method to estimate the volume of contaminated land, knowing the depth or surface. If someone can help me with this on autocad. Thank you

Bonjour,

J'ai besoin d'aide : je veux estimer à l'aide de la méthode des polygones de Theissen le volume d'un terrain contaminer connaissant la profondeur ou la surface. Si quelqu'un peut m'aider en cela sur autocad. Merci

Moderator note: English translation added

[fcernst]

We go through Thiessen polygons in 400 level Hydrology class for Civil undergrad.. mandatory Hydrology basics.. precipitation gage weighting. 

What’s the French translation here to the King’s English ?