Controlling DTM's in Autocad

I am not too familiar with drawing in autocad, but I get a lot of autocad drawings which I have to work on.
Sometimes I will receive a file exported from autocad as "3d faces" - a list of triangles that are formed from 4 sets of 3d co-ords, going from point a, to point b, to c, and back to a. These points must have an elevation, or Z co-ordinate.
What I'd like to know is what does one do in autocad to create this TIN surface in the first place, and what can you do in autocad to control the formation of the surface.
By "control" I mean if you want to draw a line which the triangle edges cannot cross, what do you draw? In other packages these might be called "breaklines". What is the autocad equivalent?
Thanks for any information.
Melanie

Maybe it is something you can't even do in Autocad without LDD?
Melanie

Happy Trails a écrit :
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Hello,
If you speak french, you can give a look here : http://www.delicad.com/autocad/flashmnt.php
Philippe

Hi
"What I'd like to know is what does one do in autocad to create this TIN surface in the first place, and what can you do in autocad to control the formation of the surface"
Try import the AutoCAD drawing into 3DMax , control can be obtained if you before importing it, in AutoCAD change all 3Dfaces's color to say Color 7 or Color "green" , if you remember this 3D Studio offer several tools to enchange even 3D faces.

I guess I'm not making myself clear.
1/    How does one create a 3D TIN surface in Autocad?
2/    What drawing objects does one make to represent ridge lines, top of slope, centre of ditch, gutter and top of curb, building bottom of walls, etc - any place where there is a well-defined, linear change of elevation?
Thanks,
Melanie
On Fri, 14 Apr 2006 15:01:45 -0400, Happy Trails
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HiHo; Look at the "mesh" command in the "help" section. BTW, LDD is easier.
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Happy Trails wrote:
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I use 2000 "out of the box". I have played with 3d without add ons. I never could find a use for 3d faces, so from the other end of things, I am guessing you want some add in software too.
regards.

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Roy,
Spherical trig is out of the question, for man or machine, when the goal is to - for example - calculate earth or gravel quantities between two surfaces. One of the most expensive operations for many civil construction projects is moving the dirt, so it's a real good idea, when bidding a job, to know how much dirt there is to move.
To evaluate a curved surface, a very good approximation is to use flat triangles, so you can use what is called a TIN - triangulated irregular network - a bunch of triangles of various sizes usually drawn between known elevation points, either ones the surveyor has measured for an existing surface, or ones you have designed for a planned surface. Since each triangle is a small flat surface, it is much easier to do any arithmetic on it.
The way most software exchanges surface designs from one package to another is by some sort of simplified representation of a TIN. If I understand correctly, it is also the same way that 3D rendering is done, but of course with many more of much finer triangles.
I do not use Autocad for doing the stuff I do, but I am presented with a design file - usually a .dwg. It rarely has any attempt at 3D representation in it, but I'd like to ask the people who create these things to include some sometime. It's sometimes a big chore just extracting the elevation data when the points are 2D and elevations are in text/blocks. The elevations are also never precise - merely close to where they should be applied.
I'd like to know what to ask them to draw - hence my original questions.
I do most of my work in Terramodel, since besides earthwork calcs, I want to produce interface files for other Trimble software which is used to do automatic grading of those surfaces. Besides being much better designed for doing this kind of 3D work, Terramodel has more seamless interfaces to these other systems for automatic grading, and also grade checking and layout for a survey guy, although Autocad is pretty good for most of this interfacing also.
I'd really like to know if plain Autocad has any commands for producing/controlling that TIN surface, othet than just drawing your own lines from 3D point to 3D point. Terramodel certainly does - that what it was made for.
Melanie

Hi
There cirtainly are limitations in ACAD but if what you want is calculations of volumes or being able to define surfaces with 3Dfaces , then there are plenty possibilities ,--- there are simple rutines that let you adjust the posision of any corner in a 3Dface , the drawing database are open for anyone who maneage the basic functions to reach and alter the numbers , ------ I think I made somthing simular to your program when I needed more advanced surfaces for boat hulls acturly there are native commands in AutoCAD that allow you to build a tarrain model from as many defination lines you want , and for any calculation , just go to the drawing database, pick the values and describe the calculations and it's there. ------- where are the point where a 3D line meet a 3Dface , well find the function in the Calc. Arx and fill in the numbers , turn a 3D face around an axis ,well the function are there ,but you need the knowleage programming it and loading the application into ACAD. Measure volumes no trouble ,describe how it is calculated and find the points surrounding the volumes , but true this do not come with vanilla acad.