[BlenderBIM] clash detection first impressions

edited June 25 in General

Hi All,
My first post here!
Below is the post from OSArch IRC forum. Hope it helps. More experiened users can add more points.

<I wanted to to check the precision of my 3d model and wanted to carry out clash detection. So I used blenderbim clash detection and a few other tools. After needing to figuring it out a bit I got bbim clash detection working. These are some points i found, not necessarily an universal issue. Also please note that these opinions are only mine and I am in no way criticising the addon itself.
blender version used 2.93.7 with bbim v0.0.220422

1) For me, the button "Add clash source" was a bit confusing, I was thinking that there is some .py file that needs to be loaded from the blenderbim user directory. So may be "Add ifc file" or "path to ifc file" would be better here? I figured it out after watching the tutorial video here https://wiki.osarch.org/index.php?title=BlenderBIM_Add-on_Clash_detection

2) Moving from one clash to the other seems to not exit at the moment. A way to navigate from one clash to another needs to be implemented in the UI.
-Open IFC viewer has a list view that one can double click.
-DDSCAD viewer also shows a list view and double clicking it highlights the clashed objects.

The issue in bbim is when highlighted objects are deselected, I was not able to re-highlight them. Running it again, didn't seem to do anything.

3) I think an option to choose the kind of clash would be good. Intersection type, Clearance type and any other, if any.

4) Getting back to regular mode after using "create snapshot" would be useful. Since I don't know how to do this with blender natively, I will have to learn it as an extra step. The whole model turns translucent and i don't know how to get back to regular mode from here. The snapshot itself has a lot of noise since all objects have the same transparency level and the actual object that has a clash cannot be identified properly even though highlighted.

5) Carrying out clash detection with all objects should also be possible, I don't know if it is present in bbim currently.

6) instead of adding syntax, which might lead to spelling and capitalisation errors, a list with a tick box would be extremely helpful. May be another option "clash all" can be provided here as well ?

7) When I press "Execute IFC clash" all objects that have a clash are selected, I don't exactly know where the clash is happening. This becomes important when the clash is less that a few millimetres. Again I find the automatic zoom to "clash object" and the way objects are highlighted with transparency settings in open ifc viewer very useful. Even the clip to clash option in DDSCAD viewer is good.

I have used DDSCAD viewer, open ifc viewer and blenderbim for clash detection of ifc files and Open ifc viewer seems to be the best of the 3 because it is the easiest to use. OIV has zero learning curve, however advance controls seem to be missing currently. For example, checking all clashes between only walls & beams, levels, etc are missing. It also doesn't highlight clashed objects in tree view which is crucial to create snapshots for making clash reports.

DDSCAD viewer is more advanced and needs a bit more learning but has a lot of features.>



  • This is great feedback! Comment 1 is a great idea and a great first easy fix for anyone wanting to making their first contribution to the code :)

    Did you save your clash results as a BCF and use the BCF viewer? That would address point 2. I think the tolerance option which can be set to negative values cover both intersection tolerances and clearance limits for point 3. Agreed for point 4, that is another nice easy contribution for someone :) For point 5, by default if you don't specify any query, it clashes all objects. Point 6 agreed, we need some help to design a UI that is both easy but flexible and retains the power of a query. For point 7, shouldn't the BCF viewer solve this?

  • @Moult
    For point 2 - I ran the IFC file in the metioned softwares, and both OIV and DDS have native support for navigation from one clash to another. I saved it as BCF only later from open ifc viewer and found that it was missing a few details ( like levels, building, site info, ifc element property etc..) when opened in BFC viewer, and I dont know which software needs to be tweaked such that the clash can be identified in the authoring software. I could see the UUID of the IFC element, but it wasn't copyable from within BCF viewer. So the BCF report was more or less useless.
    Is there a way to save to BCF from bbim after clash detection ?
    For point 3 - I didnt know that adding a negative value was possible. It would help if a small writeup is displayed explaing the same, when the cursour hovers over the value field.
    For point 5 - I dont know that was possible. I think this will all be more clear once there are some docs, or an official video tutorial release. A small learning curve is nothing to worry about. I will try these next time though.
    For point 7 - I am not sure what you mean, When you say "....BCF viewer should solve this?" Am I correct to assume that BCF viewer is integrated to bbim, and BFC viewer takes over IFCclash withing bbim for displaying clashes ? Does that mean that we need to wait till the further development of BCF viewer?

  • Yes indeed there is a built-in BCF viewer in the BlenderBIM Add-on. When you execute clashes with IfcClash, you are prompted for a filename with a .bcf extension. You can save this BCF file, then load the BCF project in the BCF panel in the scene properties. This will give you a list of clashes you can go from one to another (select one, then click the camera icon to activate the view).

  • Ah, I see! I will try this out soon. Thank you :) TNow i know bbim asks to save a bcf file format! I was wondering why it did that without prompting.

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