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PostPosted: Wed Mar 09, 2011 11:35 am 
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Hello,
I'm not entirely sure I'm posting the question in the right forum, so pardon me if I made a mistake.
Before I describe the problem let me describe what I do.
I and students work with shapefiles of towns in which we have layers for buildings, roads, blocks, etcetera.
We represent the building heights as an attribute. Sure "building height" is rather vague, but our analyses dont need to be terribly accurate, so "mean building height" is generally good enough (to calculate the building volume for example). I came into this project rather late in the game and some of the know-how has been lost.
Now sometimes we get our town data as Autocad (DWG or DXF) files.
We would like to be able to calculate the building heights from the Autocad files.
I dont have an Autocad licence, nor an Arcgis licence, and have never practiced with these, but I do have more than an inkling of what they are about.
I use Quantum Gis and MapInfo and I program in C++. I'd like to know if there is any way I can obtain
my height attribute. Would my problem be solved if the lab bought Autocad for maps? Is there a free solution?
thanks for reading


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PostPosted: Wed Mar 09, 2011 6:06 pm 
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Location: Jacksonville, Florida
It depends a lot on how the data is delivered and what software the person is sending you. If the sender is using just "vanilla" AutoCAD aka basic, chances are you will not have an attributed field for height. If they're using AutoCAD Map or Civil, they may have placed in an attributed height field.

Now if they're using vanilla AutoCAD and they have at least labeled the building height in the drawing, you could isolate that text and convert the building layouts to a polygon and join the text to that polygon, thus making a height attribute. I'm not sure is QGIS or MI offers that ability, but I know it can be done in ArcGIS.

I've done similar things with water mains I pulled from CAD data, it works well enough.

Hope this helps,
Daniel

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PostPosted: Thu Mar 10, 2011 5:39 am 
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Thankyou,
I can imagine there is another possibility, that the roof of a building is not flat and no "building height" is given in Autocad because it would not be considered very meaningful, yet the shape of the roof (as a set of triangles in space, I suppose) would in theory make it possible to calculate
an average height. It seems I would be asking that the roof triangles be put into a layer so that this computation could be done.
Now it turns out I do have some sample DXF files for a town. I'd like to know how I can tell with open source tools what kind of data is in there that might be relevant to this problem.

I do make note of your point that it will vary from supplier to supplier.


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