Topo Surface contours not accurate

[pierrre d.]

Hi everyone,

I’ve created a Toposurface using an ACAD underlay, made up of polylines representing contours shown on a site survey, to generate it. The polylines have been elevated to Z values that match the contour levels.
My problem is that the generated toposurface contours only have a partial resemblance to the contours of the ACAD underlay. Where the underlay contours smoothly and gradually bend, the toposurface contours follows them accurately, where there are sharp deviations, the toposurface contours are not even approximately accurate.
Contour intervals and levels of both the toposurface and underlay are the same – ie at 2, 4,6m etc intervals.

Is it beyond Revit’s abilities to generate accurate contours?
Is there a work-around?

Note that I’m a freshly minted user with only about a week’s experience to my credit, and may be missing a simple point somewhere.

I’ve also tried to generate the same toposurface using Points, but with even worse results. (points at an absolute level of 2m, 4m, to generate 2, 4m, etc contours. Contours generated don’t pass through points – this seems counter to logic.

What should I be doing to get credible results?

Regards

[beegee]

Topo surfaces in Revit could do with improvement and are often the subject of criticism.

If you search the forums, you will find many threads addressing this topic.

The work-around for your current situation is to use the topo generated from the dwg file and edit it and add more data points along the acad contours to force Revit to more closely match that surface. Revit triangulates between data points and this can lead to significant contour differences in some cases.

[essdubbya]

Peter

See wishlist re topo surfaces
Also you are probably aware that all contour lines are interpolations of point data taken in the field. As such they depend on the mathematical interpretation of the software that the points are imported into for representation of site grades. Generally the more points the better the interpolation. Other factors such as break-lines where walls and other changes of grade occur can make a huge difference in the way each software program behaves.
For my part I have stopped using imported contour diagrams and use 2D acad drawings with points shown by point number, code and elevation value as an underlay and manually edit each point value when creating a topo-surface. Slow but far more accurate and flexible.
One thing I have noticed when creating a topo-surface for site base-plans is the necessity to enter all known points at the time of creating the topo-surface rather than editing later. Revit does its own thing when editing and decides arbitrarily whether a point is an internal v boundary point.
Sorry about the rave
Steve W
3DL Baseplans.com

[Gadget Man]

To add to topo-surface problems, I found that when you try to move an existing topo-surface point it automatically changes to 0,000 and you have to re-type its value. It happened to me only in 7.0 (in all previous versions it was fine). Any reason? A bug?

Sorry if that problem was already reported - while I try to read EVERY post to learn as much as I can (thanks everybody for this fantastic opportunity!!!) I can't remember seeing that anywhere...

Jerry

[pierrre d.]

Hi everyone,

Have been experimenting a bit, and it seems I can increase contour accuracy by making the polyline segments smaller in the ACAD underlay used to generate the Toposurface

To Stephen,
Do you mean entering Revit points at the appropriate RLs, using an ACAD underlay survey where all data is on Z=0? I'm assuming your terminology "point number, etc" has no CAD significance. Imagine this might mean hundreds, if not thousands of points for a decent sized site.

[essdubbya]

Yep Peter

It can mean a lot of points, and you can make mistakes - high liklihood
Hence need for Revit to allow point file imports - see wishlist.
Acad file starts life as a Land Desktop file (Which can import point data from survey equipment). Points are then exploded to create a 2d file for import into Revit. A pain in the proverbial till factory addresses this problem.

Steve W

[essdubbya]

Peter

For my own convenience all points show + sign for location of point, a unique point number, and a point code such as FCE for fence, TOW for top of wall etc. It helps when determining break lines etc
Hope that explains it a bit
Steve W

[frame]

Hi, I don't see this problem with points dropping to elevation 0 when being moved. Can you provide more details?

[Gadget Man]

Hi, I don't see this problem with points dropping to elevation 0 when being moved. Can you provide more details?
Yes, I can even provide examples (see below). Together with my previous explanation they should be self-explanatory.

Regards,

Jerry :shock:

[Steve_Stafford]

I believe what you are seeing is a literal "falling" off the edge of the earth because, in Revit, the earth is a surface ("flat") not a solid ;-) . As long as a point stays within the boundary of the overall surface it should remain the elevation it is assigned.

[Yman]

I think he's right Steve. I noticed that a couple of times myself with points. You drag and no matter where you drag inside the topo area it defaults to the zero value. You have to select the point and then use the move tool to move it where you want. It used to be easy to drag the point where it needed and it remebered what elevation it was. The move tool is the only way it works right now to remember the z value.

Y

[Gadget Man]

I believe what you are seeing is a literal "falling" off the edge of the earth because, in Revit, the earth is a surface ("flat") not a solid ;-) . As long as a point stays within the boundary of the overall surface it should remain the elevation it is assigned.Even if I am not convinced (in 6.1 it didn't happen AND Revit would screem that the point is outside of boundary, wouldn't it?), perhaps I could agree with you in the first example (the first three pictures - see my previous post). In the second example (the last two pictures) all the visible points are about 3 meters inside the boundary, and I only try to move the point along an "under-laying" DWG contour (without going anyway near the boundary!) It doesn't hold the water...

Jerry

[MarkKMueller]

I have had the problem with a point changing to 0 when it was dragged in 6.1, but it was very rare. In 7.0 it happens regularly. It seems to be point specific. I can pick one point and drag it a dozen times with no change. Yet another point will go to 0 every time I drag it, and it doesn't matter where I drag it to.

Selecting move is an extra step over a simple drag, but is a workaround nonetheless. Thanks for mentioning this as I hadn't though of it.

[Wes Macaulay]

Yes, I can even provide examples (see below). Together with my previous explanation they should be self-explanatory.

Regards,

Jerry :shock:I've got the workaround for dragging points to the edge of the topo boundary:

Don't do that. :mrgreen:

(Hehehe - it's like those bugs in AutoCAD where you do a certain command, click on a certain button, scratch your left armpit while vacuuming your navel, and then it crashes. So the workaround in those situations is 'Don't do that' and we're all thinking, okay, how did they come up with this in the first place and is it really a bug?)