creating a surface from contours

[demus72]

When creating surfaces from contours I have noticed in situations where a contour makes a loop away from the adjacent contour, the program inserts points in the middle that prevent triangulation from contour to contour. I end up spending a lot of time deleting these extra points and swapping edges to get the desired result. Please see the attached image of an example of this situation. Am I doing something wrong or what should I do to improve my process of creating surfaces from contours to reduce or eliminate the additional points?

Thank you.

[AlmasSuljevic]

Hi demus72,

Without looking at your draiwng I'd first check the settings in "Adding points to flat triangle edges" in Surface contextual ribbon, Edit Surface (Minimize Flar Areas dialog). More info: http://docs.autodesk.com/CIV3D/2012/ENU/filesCUG/GUID-B6210EAA-03C9-49A5-8622-07856819589-3350.htm

[Anonymous]

What Almas posted is the first step and if you don't get the results you are looking for, then the only other option would be to flip the faces under the surface definitions to get the results you need.

[troma]

---

demus72 wrote:

...what should I do to improve my process of creating surfaces from contours...?

I would say STOP!  Never create surfaces from contours!

But in all seriousness, I know it's sometimes necessary, and I have and will do it myself.  But you have to understand, there was some real data at some point, it was converted into a contour, and now you're using that interpritation to try to get back to data.  Ever heard of something being lost in translation?  Lots of stuff is lost!

So you have a contour going on a nice senic loop.  What is the elevation in front of it?  What is the elevation behind it?  Who knows, all we have is ONE CONTOUR for this little area.  So what does C3D do when you use contours to build a surface?  It imagines that the area within the loop is just a little above or below the contour in question, depending on which way the ground is sloping.  This is called 'Minimizing Flat Areas'.  If it didn't do it, it would by default triangulate to the nearest points, which would be straight accross the loop, not  to the next contour.  Indeed, if your contour loop loops out and around a bit, it can't even trinagulate in a straight line to the next contour, the only option is to itself.  The result of tringulating from one contour to itself is obvious: an area that is totally flat.  The programmers of C3D decided to give us the option of minimizing these flat areas.  So it gueses that the area in the middle is either above or below the contour itself, depending on whether the area on the other side of the contour is above or below.  The result is as you see, extra surface points and TIN lines.  However, if you just look at the contours, you'll see this added in guesswork does a pretty good job of getting your surface contours to look the same as the ones you used to build it in the first place.  What I mean is: if you don't add in the guesswork, your surface contours will go accross the created flat area and all the way round in a circle; C3D prevents that by adding a high/low area.

Is it wrong to add in a guess for this area?  To be honest, so much information has been lost in translation, that your guess is as good as mine, and C3D's guess is probably better.  Is that area flat?  Does it slope in one straight slope to the next contour, as in your "Desired Result"?  Or is there something else going on?  The truth is we'll never know, we don't have the data, all we have is contours.

Short answer, you can turn off this option when you add the contours to the surface in the first place.  But my question to you is: Is your desired result closer to the truth than C3D's guess?