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Ste1978

AutoCAD Civil 3D - Converting topo data from a drg into a 3D Model?

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Ste1978

Hi,

 

I have received a topo drawing from a client and they have asked if it would be possible to create a 3D model of the surface. I am interested to know if this is possible. It looks like AutoCAD Civil 3D might be the package to use, but I am not sure how to convert the points on this drawing to data that civil can use to create the model.

 

Any ideas? I have attached the drg sent to me.

topo.dwg

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Tyke

Civil 3D is certainly the package that can input AutoCAD objects to form a DTM, breaklines, etc. I do it all the time and have no problems.

 

After looking at your drawing I see that it is all in 2D and you can't use 2D data to form a 3D surface. It would first need to be converted to 3D, which is not too bad as the drawing is quite small.

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ReMark

You might be able to do it with a program called SiteTopo. Check it out at www.sitetopo.com.

 

There is also another lisp program called DTM.lsp available at the CADforum that might be of some use to you although it has limited capability. It still might be worth checking out.

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Ste1978
Civil 3D is certainly the package that can input AutoCAD objects to form a DTM, breaklines, etc. I do it all the time and have no problems.

 

After looking at your drawing I see that it is all in 2D and you can't use 2D data to form a 3D surface. It would first need to be converted to 3D, which is not too bad as the drawing is quite small.

 

That's the thing I am not sure how to do, I don't know how I would convert this to 3D manually. Typical electrical draughtsman I guess, anything other than 2D schematics and I panic! I will have a play around in Civil 3D and see if I can model something. Any tips/advice appreciated!

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Ste1978
You might be able to do it with a program called SiteTopo. Check it out at www.sitetopo.com.

 

There is also another lisp program called DTM.lsp available at the CADforum that might be of some use to you although it has limited capability. It still might be worth checking out.

 

mmm...that's an interesting little program. Thanks for that!

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Organic

You could manually place a point and using the Properties pane assign the Z value that that point is supposed to have. Then loads those points into Civil 3D (30 day trial version would be fine) to make your DTM/contours. Better still would be to get the original DTM from the surveyor who produced the topographic plan.

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eldon

Whatever you do, make sure your units are consistent. The plan coordinates (x,y) appear to be in millimetres, and the elevations appear to be in metres.

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eldon

And make sure that the Point mode is made visible. It is currently set as a dot in your drawing which will hide under the cross, and you won't see the points :shock:

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Ste1978
Whatever you do, make sure your units are consistent. The plan coordinates (x,y) appear to be in millimetres, and the elevations appear to be in metres.

 

Yep, I fell into this trap after starting on this, thankfully I saw your post just in time so thanks!

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eldon

I don't know how you are getting on, but I had a slack afternoon, and here, to give you start, is your drawing with 3D points added at the level points. You will have to draw in any breaklines that are needed.

topoPlusGL.dwg

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Tyke

Interesting that Eldon converted all the levels to millimetres too, I would have converted the X and Y coordinates to metres, but there again I'm a surveyor and we are a weird bunch :wink:. I have an architect client here who always converts our drawings from metres to millimetres, even when the survey is over 2 kilometres long :o:shock::? Well if you want to work with big numbers, who am I to interfere?

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eldon

I actually scaled the drawing to metres, so that my lisp routine would work. I then scaled everything back to millimetres, so that it was familiar territory for the OP. :D

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Tyke

So Eldon used his LISP routine and I wrote a quick VBA Module that accomplishes almost the same. Instead of inserting points I inserted blocks. I also elevated the lines:wink:. Was yesterday really so boring?

 

 

topo_1.dwg

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rustysilo

Another way to do this would be to use the Surfaces > Utilities > Move text to elevation tool. Of course you would want to move all of those elevation text objects so that the node of the text was at the point marker first. Then you could add your breaklines (3d polys or feature lines) and create a surface with the text and breaklines. :wink:

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Tyke

Looks good SteG,

 

Did you work in millimetres or metres? It doesn't matter at all but I'm just curious.

 

Did you set your contour interval to 25mm (1")? Its a pretty level site with not a lot of difference in level, perhaps a different visual style would work better for you visualisation? I don't know how it was surveyed or by whom, but such small contour intervals are getting very close to the survey tolerances. I know some survey companies whose work is never better than 50 mm, but then again it depends what the purpose of the survey is. Did you manage a few break lines, TOB or BOB, kerbs, walls etc?

 

No doubt you will be looking forward to the next one :wink:

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Organic

Survey work with 50mm error? Unless you are working over huge areas (several kilometres in length), that is way out of tolerance range. Even rtk gps is good to between 10 and 20mm position (slightly worse for elevation) these days.

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Tyke

Hi Dink,

 

Sorry I wasn't a bit more precise in what I said, it was vertical accuracy that I meant, as we were discussing levels at the time. We have both Trimble and Leica *GNSS equipment and both can receive *GPS and *GLONASS, but the RTK data we get back is often quite different. We had a job recently on which both the Trimble and Leica GNSS equipment was being used side by side. Both were receiving data from 8 satellites yet on one Rover we got a vertical accuracy of 3cm and on the other 6cm!!! Don't ask me why cos I don't know.

 

And again its not always the equipment that defines the accuracy it is more often than not the operators, you can have one on the instrument and another on the prism. If the pole isn't vertical then the point surveyed is the prism/GNSS receiver not the point of the pole on the ground. How often is the pill box bubble on the pole checked for accuracy? By some people never and experience shows that these bubbles don't retain their accuracy indefinitely. How accurately is the prism sighted and at what distance? All these errors added together can have a very significant bearing on the accuracy of the surveyed position of the point on the ground. Some surveyors work to much higher tolerances than others and not everybody has an automatic target lock on their total station.

 

*GNSS = equipment that receives satellite data http://en.wikipedia.org/wiki/Global_navigation_satellite_system

*GPS = American satellites http://en.wikipedia.org/wiki/Global_Positioning_System

*GLONASS = Russian satellites http://en.wikipedia.org/wiki/GLONASS

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