topic Re: Getting contour lines from a mesh in Modeling

Getting contour lines from a mesh

Anonymous — Thu, 25 May 2023 15:09:09 GMT

I know how to apply 2d contour lines to a mesh such that the mesh takes on the 3-d characteristics of my 2-d survey; I'm wondering if there's a way to go the other way.

That is if I start with a mesh and manipulate the mesh by elevating nodes, just generally shifting parts of the mesh around can I then have it tell me what the contour lines are? I am reminded of a tool, which I believe was called "contour", in Form-Z which I always used for making cnc templates out of irregular objects.

Basically, I'd like to be able to just grab points on a mesh, move them where ever the new architecture suggests they should be and then have ArchiCAD tell me what the contours would be.

Re: Getting contour lines from a mesh

David Maudlin — Fri, 27 Mar 2009 15:12:26 GMT

Mickey:

One method to extract this information from the mesh and apply to the 2D view is:

1. Set your 3D Window Settings to Internal Engine, Hidden Line
2. Set your Parallel Projection Settings to Top View, Azimuth = 270˚
3. With the mesh selected, right-click and select Show Selection/Marquee in 3D (so only the mesh appears in the 3D Window).
4. Set your 3D Cutting Planes: In the “Z” box, enter the height of the contour, click the “Z” icon to lock it, then draw the Z Cutting Plane in the window above, click above the line to remove all above, set the Fill Material & Edge of Pen Cuts to Custom, and set the pen number for a unique pen (this will help in seeing and selecting the lines).
5. Activate 3D Cutaway
6. Go to the 3D Window, your mesh will be cut at the contour height, the cut line will be the pen previously selected
* (see later post below)
7. Select the Marquee Tool, flat marquee option, select the area around the contour line and copy
8. In the Copy dialog box that appears, select Scaled Drawing, Edges, and Remove Redundant Lines
9. Go to the 2D Window and Paste, the contour lines will come in over the mesh matching their position from the 3D Window
10. Repeat steps 4 to 9 for each contour level

Yes, this is not very automatic, but will give an accurate contour map of the mesh. I don’t know if using Solid Element Operations instead of the 3D Cutting Planes is easier. It would be good to have a contour display option in 2D for the Mesh Tool (would need to be able to set the contour interval, Reference Level, line pen and line type for this to be useful).

David

Re: Getting contour lines from a mesh

Thomas Holm — Fri, 27 Mar 2009 15:36:28 GMT

David,

this is a great tip, you should absolutely post it in the Wiki!

Edited:

I don't think that using SEO instead of cutting planes would make it easier, however I could imagine using that, combining with appropriate layer combos and one invisible SEO operator and a saved view for each contour could make it possible to overlay transparent views in a layout and make the contour map auto-update with terrain changes instead of being static like you describe.

Maybe too much work except for special occasions, though.

Re: Getting contour lines from a mesh

David Maudlin — Fri, 27 Mar 2009 22:13:38 GMT

Thomas wrote:
this is a great tip, you should absolutely post it in the Wiki!

Thanks Thomas. I rewrote some of the text and created images to go with the text, but have hit the wall with the Wiki (I have never tried to post to a Wiki, so I am probably missing something obvious to the experienced). From the screen shot you can see that I am logged in, and I had created a new page "Extracting Contours from Mesh", but when I then click on the TechNote Template, this same page just reloads. I have read the HowToWriteArticles page, but I don't see what step I am missing to get started. If anyone has some insight, that would be great.

David

Re: Getting contour lines from a mesh

Thomas Holm — Sun, 29 Mar 2009 01:23:20 GMT

Well David, I'm sorry I'm not that experienced. I suggest you PM Karl Ottenstein (if he doesn't post in this thread before you do).

Re: Getting contour lines from a mesh

David Maudlin — Sun, 29 Mar 2009 12:23:44 GMT

As a footnote to my method above after step 6:
*The 3D Window with the Mesh and Cutting Plane can be preserved with a 3D View: after generating the 3D Window, use the Organizer to pull the Generic Axonometry from the 3D List into the View Map, give the view a descriptive name (for example: Contour -10’), click the Settings button and click the Get Current Window’s Settings to save the settings of the 3D Window, including the Cutting Plane. This allows the contours to be regenerated more quickly if the mesh is changed.

David

Re: Getting contour lines from a mesh

Laszlo Nagy — Sun, 29 Mar 2009 17:16:30 GMT

Nice tip,
In any case, I have copied it into the Tips and Trick Forum.

Re: Getting contour lines from a mesh

rocorona — Sun, 29 Mar 2009 20:53:02 GMT

Very interesting. Starting from the procedure described by David and the hint of Thomas, I've made a simple GDL object that can do it in a semi-automatic way.

Just select the Mesh on the plan, and save it as a Library part, then put the name of this object in my ContourMaker.
You can set the starting level, the contours step and pencolor. For 2D the line type too.

The original mesh can be shown or hidden. If it is visible, the contour lines can be lifted a little bit, to avoid penetration in the solid body.

Re: Getting contour lines from a mesh

rocorona — Sun, 29 Mar 2009 20:54:55 GMT

Here the Object

Re: Getting contour lines from a mesh

Thomas Holm — Sun, 29 Mar 2009 21:43:01 GMT

Fantastic, Roberto! Please put this in the object depository!
(Edited:) This thing adresses a long-standing wish of mine - an easy way to add contours to edited earth fill meshes on site plans. Thanks again!

Re: Getting contour lines from a mesh

rocorona — Mon, 30 Mar 2009 21:19:58 GMT

Just made in AC9 format, with a preview image, and posted it in the depository. Not sure of the category. I've put it in "General".

And finally tested... Found it is fast enough, also if the script is not so clever. It issues a "CALL" and a SEO operation for each contour line.
I think it can be done with only ONE call, using a series of planes as operator, but the planes needs to be large enough to cover the Mesh. Maybe this could be done using the RETURNED_PARAMETERS to know the A and B sizes of the mesh-object?.

Did a test of what happens if the original Mesh is updated... Simply selected it and re-saved as library object, overwriting the previous one. And the contour lines magically updates accordingly.

Re: Getting contour lines from a mesh

Anonymous — Tue, 31 Mar 2009 01:46:30 GMT

Hello Roberto,
I downloaded your object and looked at the script
and found that you used the CUTPLANE command
to do the cutting of the object called in the script
rather than SEO (or the group operations equivalent)
as you stated. I changed the "contour line step"
parameter from 3'-3 3/8" to 1'-0" and got an error
saying "group operations error at line 21 of the 3D
script of...etc". I checked script but no errors are reported.
Looking at the script I can't see what the problem might be.

Why is calling the object more than once not desirable ?
I can see using a series of slabs separated by a very small
space and using group operations to leave very thin slices
of the object could be done but why ? The way you have done
it seem perfectly reasonable and economical.
Thanks,
Peter Devlin

Re: Getting contour lines from a mesh

rocorona — Tue, 31 Mar 2009 06:22:16 GMT

Peter wrote:
Hello Roberto,
I downloaded your object and looked at the script
and found that you used the CUTPLANE command
to do the cutting of the object called in the script
rather than SEO (or the group operations equivalent)
as you stated.

The SEO operation I was referring to is ISECTLINES. It is a special form of intersection, not present in ArchiCAD itself but only in GDL, that generate the intersection lines, without surfaces. I use it with the full mesh as the target and the cut mesh as the operator. This way I can do the whole thing without knowing the mesh size (the cutplane is infinite).

I changed the "contour line step"
parameter from 3'-3 3/8" to 1'-0" and got an error
saying "group operations error at line 21 of the 3D
script of...etc". I checked script but no errors are reported.
Looking at the script I can't see what the problem might be.

Sorry... it was metric.
I get the same error when I try to cut some other library element. It should work with any element, but I've tested it with a sofa and 3D people, to get some new representation... but with no luck. It worked with some of the basic shapes (cone, sphere).
Line 21 has the ISECTLINES command. It can have something to do with "no solid" operator (wireframe or simple surface).

Why is calling the object more than once not desirable ?

Only for the "waste" of time and computing resources! . I am an "old school" programmer (the generation that caused the millennium bug, just to save 2 bytes)

I can see using a series of slabs separated by a very small
space and using group operations to leave very thin slices
of the object could be done but why ?

As I said , this requires to know the size of the Mesh, in order to make the slabs big enough.

Re: Getting contour lines from a mesh

Anonymous — Tue, 31 Mar 2009 21:19:01 GMT

WOW!!! y'all have been busy since I posted my question. David, not particularly automatic, but this will certainly come in handy from time to time.

Thanks everybody for your tips.

Re: Getting contour lines from a mesh

David Maudlin — Thu, 09 Apr 2009 11:59:22 GMT

I added a page to my web site illustrating the method outlined near the beginning of this thread:

Extracting Contour Lines From a Mesh

David

900

Re: Getting contour lines from a mesh

Anonymous — Thu, 09 Apr 2009 13:43:10 GMT

Roberto,
I really like this object - thanks alot.

Re: Getting contour lines from a mesh

rocorona — Thu, 09 Apr 2009 19:19:30 GMT

Mark wrote:
Roberto,
I really like this object - thanks alot.

Thanks for the appreciation. And it is so simple to make, that I'm surprised no one (including me) did it before

Re: Getting contour lines from a mesh

Anonymous — Thu, 09 Apr 2009 23:27:55 GMT

your right it is relatively simple but very useful, im sure theres other features you could add to objects by this principal....

Re: Getting contour lines from a mesh

R Muller — Thu, 05 Nov 2009 19:15:35 GMT

Thanks for the tips, guys.

I tried the library part, but no luck using it in AC13 (it hangs ArchiCAD on my Mac).

David, your cutting planes method worked, but I am clumsy using the cutting planes dialog box and I wanted something more automatic. I am working on a steep 10-acre site and need to draw 16 or more contour lines to evaluate various grading options.

I used a vertical stack of slabs to generate the contour lines, with SEO to automatically update them as the mesh changes. This generates all 16 contour lines in one step. It allows me to concentrate on the high points, valleys, and various spot elevations that I want to see on the site, and let the contours draw themselves.

Here are the instructions that I wrote for myself, so I can remember what I did the next time I need it. David, I have incorporated your technique for getting scaled lines out of a 3D view. I would never have come up with this all by myself.

1. Decide on your contour interval. For this discussion, I will assume a 2’ contour interval. Define the elevations of your lowest and highest contour lines. For this example, I will assume the lowest contour is 102’ and the highest is 124’.

2. On a separate layer, create a slab of the same thickness as the contour interval, with the bottom of the slab at the elevation of your lowest contour. For this example, this is a 2’ thick slab with top elevation 104’. Note that the top of this slab will generate a line for elevation 104’ and the bottom will generate a line for elevation 102’. Set the pen color and line type for the slab outlines to match what you want for your contour lines. The slab should completely cover your mesh, but it does not need to be trimmed to the mesh shape.

3. Multiply the slab to create slabs at elevation 108’, 112’, 116’, etc. You want to have a gap of one contour interval between each successive slab. Each slab will generate two contour lines: one for its top surface, and one for the bottom surface. Group the vertical array of slabs.

4. Use solid element operations to intersect the slabs with the mesh. The slabs are the target, the mesh is the operator.

5. Set 3D window settings to internal engine, hidden line. Set 3D projection settings to parallel, top view.

6. Select the group of slabs (but not the mesh), right click, show selection in 3D. You will see your contours. (See note below if you do not see any contours.)

7. Save this 3D view, with a name such as “generate mesh contours”.

8. Using the marquee tool (flat geometry method) in the 3D window, select the contours. Copy. In the copy dialog box, choose “Scaled Drawing”, “Edges”, “Remove Redundant Lines”.

9. Go to your 2D view, set the layer setting to your site plan. Paste. The contour lines will come in on the ArchiCAD layer at the original mesh/ slab location, which should be where you want them to be. In some cases they will come in behind other elements, and you won’t see them yet.

10. Undo/ redo the Paste to select all the contour lines, bring to the front if necessary, and assign to your chosen layer. You may wish to group the lines.

11. If you change your mesh, all you need to do is click on your “generate mesh contours” view to regenerate the new contours. Then erase the current contours and repeat steps 8-10 to revise the contours in the plan.

Note: if you do not see any contours in step 6, it may be because your slabs are touching, rather than gap-toothed. You want to omit alternate slabs, as noted in step 3. ArchiCAD removes the intersection lines in 3D view between two slabs where the top of one is the same as the bottom of the next.

Leave the group of slabs in your model, as a way of automatically revising your contours if you change your mesh.

Re: Getting contour lines from a mesh

Nader Belal — Wed, 19 Apr 2017 18:14:21 GMT

Hi everyone,

I'm fully aware that this topic is old, and could be considered even solved, but I just have seen it now, and I think I can contribute solving this issue.

This solution is easy to implement, and it's done in a step by step manner, but it requires the use of Grasshopper.

You can check at here

Anyway, I hope that with it you will get the result that you hoped for.