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 :

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

 

You need some sort of civil add-on for AutoCAD, like LDT, SurvCADD,
Eagle Point, etc.

 

You can't with vanilla AutoCAD depending on your definition of 'TIN
surface'. If you simply mean a series of adjoining 3DFace entities, I
suppose you could create this by hand. But generally speaking a 'TIN
Surface' is defined in a file and the 3Dfaces are just a representation
of the defined surface, just as contour lines are.

Depends on the 3rd party software. SurvCADD for example will use an
LINE, LWPOLYLINE, or POLYLINE entity (3D or 2D)

 

HiHo;
Look at the "mesh" command in the "help" section.
BTW, LDD is easier.

 

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.