Tuesday, May 01, 2012

Five Minutes with a Toposurface

I created a video to describe what happens when Revit contours don't quite match up with the underlying cad file contours that were used to generate a toposurface. The first part of the video explains that the Site Settings usually don't match the contour interval settings of the cad source file. Changing these settings is often enough.

When we want Revit to provide more contours than the source file provides it can but that's where we start getting some distortion of the contour lines we see. The rest of the video shows how to manipulate the contour lines with additional points to help Revit sort it all out.

Keep in mind that Revit creates triangles between points. You can see these if you use Visibility/Graphics to turn them on.

This is what the triangulation looks like before adding an extra point to help Revit draw the contour more accurately.

This is what the triangulation looks like after adding the extra point.

Here's the video embedded or watch it at OpEd Videos or You Tube instead.


Alfredo Medina said...

That is why I think the most accurate method is the one that uses a .csv file with a list of points. I have made tests using different methods with a complex site, and the winner of the precision prize has always been the .csv method.

Steve said...

I think we tend to infer from a cad file that the contour lines "between points" are accurate when most likely they are an approximation.

Revit makes this approximation more apparent when we let it interpolate points between actual contour elevation points. If we don't let it do that, there are far fewer so called discrepancies if any. At least we don't have to look at them.

The default settings create an opportunity for confusion. Just making sure that the settings match the interval being used in the supplied reference file will go a long way toward "cleaning things up".

Alfredo Medina said...

Yes, any method is an approximation; what I meant to say is that the method that creates the most faithful reproduction of the original 3d drawing from CAD is the .csv method. It does not have to be "fixed" with the introduction of new points, as suggested in this thread: http://www.revitforum.org/architecture-general-revit-questions/7121-problem-inaccurate-toposurface.html

Steve said...

I suspect the difference you describe using the .csv eliminates Revit deciding where points should fall along the contour "lines" in the cad file. Otherwise I wouldn't expect any difference. Regardless, most of the time, all that is needed is making the contour interval match the source data.

Alfredo Medina said...

Great video, by the way, explaining how a simple setting in that dialog box can help a lot in getting a good result with sites created by this method.

Alfredo Medina said...

Hmm... I guess the .csv method might just bypass those settings, and simply work on the points.

Daniel Benedict said...

Hi Steve

Regarding the creation of a Surface in Revit using surveyors data. Ideally get the surveyor to create a 3D triangle file and use that to create the surface.

The issue with contours, are as you suggested, as being approximate and you can see the error with the contours lines, (CAD v Revit). This could because the surveyor might have swapped the edge of the triangle to show a smoother contour. Also Revit dosn't have the ability to use break lines as Civil3D does.

The issue using a CSV file would be not all points are on the surface.

Thanks for help over the years, much appreciated.

Melbourne, Aust.