topic Removing a building from surface creation for contours in AutoCAD Map 3D Forum

Removing a building from surface creation for contours

nara7ZXKX — Wed, 15 May 2024 18:02:13 GMT

Hello All,

I want to create a surface from a point cloud and add contours to it in Map 3D.

In Recap, I tried the Automatic Ground Classification and unfortunately it omitted a large chunk of the actual ground beneath trees from the front yard of this very flat property. So, instead, I manually deleted as much as I could. Then attached the rcp to the Map 3D dwg and used MAPCREATEPCSURFACE. I created contours at 0.5’ but the surface still included the voided space of the building. How do I properly trim or fence that out? Please do not suggest using Civil 3D as we don't want to pay for that.

Thanks!

Re: Removing a building from surface creation for contours

ChicagoLooper — Thu, 16 May 2024 14:54:25 GMT

@nara7ZXKX

Your workflow to create your surface is not ideal.

The 'instruments' gathering the point cloud data cannot see (or detect) what's underneath the building. That mean's your data includes the roof surface but not what's underneath.

The LiDAR is not penetrating the building's roof because it's not like a leaf on a tree. Where vegetation is flexible (penetrable) and LiDAR can go beyond the tree canopy to detect low bushes. A roof, however, is too rigid. LiDAR can even go beyond bush level and detect 'ground surface' because like a leaf bushes are penetrable too. If LiDAR could penetrate a roof why wouldn't it give you data for the carpet on the second floor? Or the tile on the first floor kitchen? Or the concrete floor in the basement? Just because you remove the building doesn't mean you'll get the the ground surface under the building.

To fill in the blank areas where the buildings have been removed, you'll need to use judgement and recreate the surface. And that's a manual operation, not automated.

In Civil 3D, you could fill in using feature lines, cogo points, or contours, to name a few. You may also create new small surfaces, representing the blank areas, then use the Paste Surface feature. Depending on how well you create them, your new surfaces will blend in nicely with the existing surface.

I already know you won't like this answer but Civil 3D is more suited to creating, or filling in, a surface, not Map 3D. M3D is more suited to geospatial analysis whereas C3D is better at surface creation and subsurface infrastructure.

Re: Removing a building from surface creation for contours

nara7ZXKX — Thu, 16 May 2024 18:20:39 GMT

Thank you for the reply @ChicagoLooper

By no means am I wishing to infer the ground beneath the envelope of the building. We're only interested in the garden space. That includes elevations under the eaves up to the foundations. So, what I'd like to do is create the surface that on the plan view, stops where structural features are and does not extrapolate through them. I want the surface to have the polygon shape of the planar slice effectively.

Once I exported it into a regular dwg, in AutoCAD Arc, I then selected to create a new clipping boundary and pressed p to make it a polygon and traced around where I wanted to exclude.

This is where it's gone messy: I had to explode the contours to trim them to the new boundary, but as they became tiny chunks of the linework, it wasn't a tidy trim and delete and then the program got hung up and crashed when I tried to convert the contours back into polylines using pedit.

Re: Removing a building from surface creation for contours

nara7ZXKX — Thu, 23 May 2024 22:06:45 GMT

I've come back to working on this.... In a post I created in the ReCAP forum, I was directed to try using CloudCompare and it's proving a little more in line with what I'm after.

This is from an example that the architect provided to show us what he'd like as a dxf:

This is a different property to the one I first mentioned, but for the same client. There is a 10' climb from the driveway to the backyard, but when I saved the Map3D file into a version I can open in regular AutoCAD, the surface and contours appear completely flat. So that's not ideal.

Re: Removing a building from surface creation for contours

O_Eckmann — Tue, 28 May 2024 19:10:47 GMT

Hi @nara7ZXKX ,

Once you've calculated your surface as TIF file and contour lines as SDF, you have 3 more steps :

- MAPIMPORT your SDF file with object data at minimum elevation

- transfert OD Elevation as CAD property Elevation to polylines : with my plugin or by request and alter property

- MAPTRIM to cut/remove portion of polylines inside (or outside) of any closed area

Here is screencast

(view in My Videos)

Re: Removing a building from surface creation for contours

nara7ZXKX — Tue, 28 May 2024 20:51:07 GMT

Merci, Olivier!

That plug in looks very useful indeed! Unfortunately, I am unable to download it so am sending you an email.