I searched for the solution to this, but I found this thread, and sadly, there wasn't much in the way of a solution.
After playing around with a few things, I ended up taking the existing surface and displayed nothing but triangles, and extracted them.
I copied the triangles into a new drawing, and extruded them 2 feet. This gave me a 3D solid with the top face 2 feet offest from the orginal triangles normals.
I switched to conceptual view style and exploded the 3D solids giving me regions.
I then selected all the upper regions (this was the most tedious part), then hid them using object isolation. What was left was the bottom regions (the triangles I originally started out with), and the sides. I deleted them and ended object isolation mode so that all I was left with was the top regions.
I then switched back to 2D mode and exploded the regions, and converted the lines to polylines. I then created a surface and added these polylines as contours. Once the surface was created with the polylines as its definition, I showed nothing but points in the surface style and extracted them.
After the points were extracted, I was left with a number of point clusters very close together due to the triangles being extracted perpenducular to their normals. I used MAPCLEAN to snap clustered nodes, and used a tolerance value big enough to cover a cluster. This left me with one point per cluster.
Once I had the points, I converted those into COGO points, then exported them to a point data file (so I didn't have to go through the headache of recreating this again).
In a new drawing I created a surface out of this point file and saved it as a data shortcut.
Once it was all done and over, I cut cross sections showing the original surface and the new surface, and they came out nearly perfect. You may need to swap alot of edges to make it correct. When swapping the edges, it may be easier to create a reference to the original surface so that you can make sure the contours match up (of course they will be a bit staggered along slopes).
I know this is an old thread, but if someone Googles it like I did, hopefully this will help out a bit.
Good solution - but you must have far too much time on your hands....
They pay me by the hour.
You've earned your money for this then.....
Very nice solution. Using Mapclean was the way to clean up the clustered points. If I'd thought of that I could have done it with my original lisp. It created the points so all that was needed was to clean them up.
Allen, If you update your lisp, I would be very interested in it. Anything to automate this, especially the region selecting would be extremely valueble.
I'll see what I can do. As I've said in the other threads, offsetting surfaces isn't something I've had to do. It was just an exercise in using lisp and the Geometry Calculator. I haven't done any lisp programming in years. I've never tried my lisp in Civil 3D or in any recent version of Autocad.
What the original lisp would do is to take 3DFaces and create points at a normal vector to the vertices. So if I can get it to run in C3D I might get you to the step where you have points. Then you could use Mapclean. I'll see if I can get to it later in the week.
For anyone who does a lot of surface offsetting. I know that QuickSurf used to be able to do this. I haven't use this software in over 20 years. So I'm not up on it's current capabilities.
This really begs the question - why does this functionality not exist in the basic C3D product?? Lack of demand, too difficult to program??
The main application would be for the design of landfill cells, dams, flood barriers etc all of which are viable markets for C3D. Someone will no doubt chime in and say the Sub Assembly Composer could do this but not everything lends iself to corridor modeling...!!
What the original lisp does sounds like it saves a ton of work. Basically cutting out the extruding, selecting regions, converting them to poly lines, adding those to a surface and then extracting points could all be skipped. So basically most of the work.
Sounds like no changes are needed to the orginal. Can't wait to try it. Is there a download link or the code I can get from you?
Thanks for your help on something you don't even have a use for. Much appreciated.
Everything you said is accurate to my situation. I create very complex grading designs for fertilizer companys waste, as well as power plants ash piles. When you need to build a ramp up the side of a gypsum stack, corridors just don't work as you would like them to. Most of my work ends up being feature lines with grading and infills.
On this particular project, I'm working on a pond that was built about 10 years back and we need to take what is existing and add a 2 foot cover to it. No easy way to do that accurately.
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