Topic: (C3D 08) What's up with this surface?

[Guest]

See attached image.

The contours that jump off the 390 contour and dive into the building face.... what the dilly o?  I've created an existing surface from existing contour (polyline) data - Ah ah ahhhh.... Before you say it... This is all we were given.  If it'll help, I can post the file.  What's making it do this?  It looks okay in 3D, but the plan view looks.... um.... fake!

[sinc]

Is the building finish floor also at elev=390?

If so, there is no way to control how contours are drawn across flat surfaces.  If you want to force them to appear in a certain way, you can add some additional data.  For example, if you add an additional breakline between your contour and your building that is at 390.001, it should make the funky lines disappear, as the area between the contour and the building will now be (ever so slightly) higher than 390.

[Guest]

Here's the file...  I used the building outline as a non-destructive, hiding boundary.  Probably not the correct thing to do??

[mjfarrell]

If I add the building line to the surface prior to adding the contours, and points my result produces no contours inside the building.

[Guest]

If I add the building line to the surface prior to adding the contours, and points my result produces no contours inside the building.

How did you add the building line to the surface?  Did you add it as contour data?  Can you post the file you modified?


Also, what is considered "best practice" when creating an existing grade surface from contours/plines/points when that's all you are given?

[mjfarrell]

Matt I added the building outline as a Standard breakline to the surface.
I did this FIRST so that the TIN would begin by being defined ONLY by the building points.
Then I trimmed the ends of the contours that overlapped the building, and added the contours.
I stopped there as it was more a proof of concept, so I did not add the points. (note some
of those points are inside the building envelope, so they will need to be excluded.

As to best practice, in this instance one would add the major breakline features, then the contour data, followed by the point data. We cover several existing ground scenarios in my classes.

Should I finish this puppy up and post it for you, or would you rather follow the above steps first?

[Guest]

Should I finish this puppy up and post it for you, or would you rather follow the above steps first?

Finish it but don't post it (yet).  I want to mess around with my file and see what I can come up with.  Later on, I'll compare mine to yours and see where I went wrong.

Thanks.

[mjfarrell]

I like that attitiude!  You would do well in class. 

[Guest]

Quick question... What did you mean when you said you "trimmed the ends of the contours that overlapped the building"??  There aren't any contours that overlap the building.   

[mjfarrell]

uh, yes there were (are) I offset that building line .1 and trimmed the contours away from the building pad line

[Guest]

uh, yes there were (are) I offset that building line .1 and trimmed the contours away from the building pad line

Why did you offset it 0.1?  Did you use the offseted (is that even a word?) line as the breakline?

[mjfarrell]

Experience


I know the process is or was to draw the contour lines right up to the building.
I also know that unless we are going to model the building pad (stem wall) that the contours
do not actually get right up on the building. So I trimmed them back, as little as practical
to keep the data as close to what I was given without introducing crossing points in either
the building breakline OR the contour data.

[Guest]

Experience


I know the process is or was to draw the contour lines right up to the building.
I also know that unless we are going to model the building pad (stem wall) that the contours
do not actually get right up on the building. So I trimmed them back, as little as practical
to keep the data as close to what I was given without introducing crossing points in either
the building breakline OR the contour data.

Okay.... so just to clarify... you offset the building line .1, trimmed the contours that overlapped that offseted line, added the original building outline as a standard breakline then added the trimmed contours?  Do I have it right?

[mjfarrell]

correct, there were only 4 or 5 that wanted to be trimmed

[mjfarrell]

I'm starting to wonder, where this surface came from? As in was it modeled; or were the contour lines drawn to represent a design that was never modeled? What do you know of the origin of these underlying 'contours', and why did you not get the terrain model from the source?  Just curious, as always.