How to weed a polyline / contour to reduce a surface size that was created from contours

[RD-JLD-Eng]

Hello all,

I have a project that I flew with the drone to get the survey data. The software that I use to process the drone data is 3DSurvey. The software generates a good quality contours that I usually transfer into dxf and bring into civil 3d and create surface out of the contours by adding them to the surface. The problem I usually have is the contours generated by the software has tons of vertices which create a big size surface. This is usually not a big problem when I work on small site but I currently have a big size project and when created a surface out of the contours the file size became huge. Is there a way to weed the contour lines or to transfer the surface into a different format so I can have a smaller size? 

Any help would be appreciated. 

Thank you

[SoaresASBCAD · Accepted solution]

As i understand it, just add a border and it will solve 

[RD-JLD-Eng]

Thank you for the reply. I am not sure I understand. Can you please elaborate? The surface I usually create already has a border.

Thank you 

[SoaresASBCAD · Accepted solution]

Yes 

[SoaresASBCAD · Accepted solution]

Can you make it available? 

[RD-JLD-Eng]

The file size for the project I am having issues with is bigger than that max allowed size to upload. I have uploaded a similar contours with surface for a smaller project. Thanks alot

[Pointdump · Accepted solution]

Hi Raed,
You might be able to reduce the number of vertices with MAPCLEAN, but have you considered bringing the drone data in directly as a point cloud?
Dave

[RD-JLD-Eng]

Thank you for the reply. No, I actually brought the contours in not the point cloud. If I bring the pint cloud and create a surface out of them, the surface size will be much less but will not be as accurate as when I bring the contours. The contours generated from the drone are a lot more accurate. 

[Pointdump · Accepted solution]

Raed,
With command MAPCLEAN you can use Simplify Objects and Dissolve Pseudo Nodes Cleanup Actions. I used a tolerance of "0.5" and hugely reduced the number of vertices in your drawing. But that changes the contours.
Reconsider using the original point cloud data. Contours are not the best data to build a surface with.
Dave

[ChrisRS · Accepted solution]

I agree with @Pointdump in post 9: "Reconsider using the original point cloud data. Contours are not the best data to build a surface with".

I think Civil 3D users need accurate surface models and good-looking contours.

Surfaces model the available "ground" data.

Contours are representations of the surface model.

The imported 3DSurvey contours are a representation of the 3DSurvey surface model.

A surface modeled from the 3DSurvey contours is a representation of the contours, not the underlying source surface.

Specifically, contour-based surfaces do not accurately represent ridges and valleys in areas where contours double back on themselves. This is more evident in flat areas. This is the model (drawing) that you provided. The surface is stylized with 0.25' contours.  The cyan areas are much flatter than expected.

Here is a detailed view of the eastern area.

They would be different if you were to hand draw the intermediate contours.

I suggest that they would be more accurate.

If I were creating a surface from surveyed points, I would include break lines to ensure that ridges and valleys were modeled correctly.

The point cloud process says, "we don't need no stinking break lines."

This is correct because you have a fractillion points available and more than enough information to model the surface.  When you extract contours from this model, you get an accurate representation of the contour paths but no information on the areas between contour lines.

Does it matter? Is it good enough? I am a great fan of good enough.

Sometimes it is good enough; sometimes, it is not.

Here are profiles along the ridges and valleys (washes.)

The ridgeline inaccuracies are probably acceptable for manually determining catchments but are problematic when examining overtopping conditions.

The valley flowlines are problematic. Feature lines draped on the surface do not show reasonably accurate slopes. Water drops stop at flat areas that sometimes occur. Surface-based cross-sections are not accurate. 

I am indeed capable of estimating and scaling, and interpolating. I have done it for decades. With a point cloud level of detail, I should not still have to guesstimate.

I am unsure what it is, but there is something better than contour-based surface modeling.

End of rant!

[neilyj666 · Accepted solution]

As others have said, contours are probably the last resort when it comes to objects used for building a robust surface. however sometime they are the only thing you have to work with in which case SURFACE SMOOTHING may reduce the surface considerably. Use Edge contraction and a 60-80% reduction but prepare for a long wait while it processes

[jmayo-EE · Accepted solution]

I'll also agree with the other posts here. Contours are not the most accurate surface surface data. Contours are computed form the points.  The points, whether conventionally shot or acquired in a cloud, are the only accurate data. Everything else on any survey is interpolated. As Neil said, Surface Simplification is probably the best way to get a usable surface as it pertains to performance. Simplify the surface. Save it in it's own file and data referenced (not xref) into your work so you don't carry those contours that created the tin into your project.

John 

[RD-JLD-Eng]

Chris, thank you so much for looking into this. Great information and details. you rock!

[ChrisRS]

You are welcome.

Please let us know if you find a better method.

[fcernst]

How are you determining the drone software contour output is more accurate than Civil 3D contour output?