Coplanar and open edges

[DavidOConnor]

I'm fairly sure this is impossible, but I have to ask.

Is there a solution in CityEngine to avoid coplanar and open edges on models?  When I split scopes away, it detaches faces from each other.  So when I import the models into 3ds Max, the model looks perfect.  However, the some of the polygons are 'floating', i.e. not attached to the polygons nearby.  It isn't a bug, I know, it is just the way the CGA rules operate using a shape tree.

Sometimes, I can weld 'floating' polygons together if there is a handy vertex nearby, but often there isn't.  Is there a solution for these orphan polygons, to avoid coplanar and open edges?

Just to emphasize, the models look perfect in 3ds Max and it isn't a bug.  Thanks for reading!

[LechKar_owicz]

If I understand you correctly you mean the situation shown on an attached image
[ATTACH=CONFIG]16764[/ATTACH]
Red and green horizontal edges are coplanar but they are not connected. It that's what troubles you, then I'll tell you that it troubles me a bit too. That's just not good topology of the model. For the purpose of visualisations I guess it's ok when it looks ok. But if you want to process the model further in some other 3D graphics program, especially if it involves some automatic processing, I'm affraid it can be a problem. I suspect it can also be a problem if you export the model to a multipatch (for ArcGIS) and you want to use it with some of ArcGIS tools which require the multipatches to be closed-geometry. I guess the model with open edges isn't closed, am I right? I can't confirm if there realy is a problem here, because the trial version I have installed doesn't allow for any kind of export.
One of solutions I tried is to use offset operator insted of extensive use of split. This way you have a kind of equivalnet of extrude and scale operation from traditional 3D graphics. One problem is that you can only set one offset value which will be applied to all the edges of a face. I tried using shapeO operator which allows for defining offset for every edge of a face separately ie. separately for front edge, for left edge etc., but for some reason I can't get it to work with faces different than lots' shapefiles.
The second picture shows the use of offset operator for tiling windows.
[ATTACH=CONFIG]16765[/ATTACH]

Ofcourse this doesn't solve the problem with connecting eg. a front fasade with sides of the building and its roof without the open edges...

[DavidOConnor]

Hi Ledrom

Thanks for your reply, and your solution.

You are exactly right, a watertight mesh would be useful 😄

Cheers, David

[LechKar_owicz]

There is also the possibility that when making splits CityEngine uses n-gones to deal with apparently open edges and triangulates them during export to some external format, but I can't check it because I have only the trial version which comes with all the export options blocked.
As my company is interested in CityEngine to ArcGIS workflow I'd appreciate if someone confirmed or disproved my doubts about closeness or non-closeness of multipatches (made using split operator) exported to ArcGIS.

[CarrieDavis]

Hi Ledrom,

I�??m a support analyst at Esri and not a CityEngine expert (sorry), but I do work with the 3D Analyst tools in ArcGIS.  I was checking out the forums and thought I maybe I could at least provide some answer to your question about how particular models would function as multipatches.  I used the following rules to split models in CityEngine 2011.2 and then exported them as Collada using defaults.

[ATTACH=CONFIG]16932[/ATTACH] [ATTACH=CONFIG]16933[/ATTACH]

The multipatches look the same in ArcScene, but are not closed.   It is possible there are export option changes with the upcoming CityEngine 2012 or rule parameters that I am unaware of that would assist you in exporting a closed geometry model.  My façade rule based building was hollow so definitely did not pass the Is Closed 3D tool test. I understand that you want enclosed multipatches for use with the 3D Analysis tools.  In version 10.1 of ArcGIS there is a new tool available called Enclose Multipatch.  This tool successfully created closed multipatches from these imported models.
 
Enclose Multipatch (version 10.1 help documentation)
http://resources.arcgis.com/en/help/main/10.1/index.html#/Enclose_Multipatch/00q9000000mn000000/

I would also suggest discussing the options for trial versions with your Esri account manager if you would like to test this.

Hope this helps,  Carrie

[MatthiasBuehler1]

hi !

Thanks for all inputs of the posts before.

CityEngine can merge those faces which share the same material. That is defined in the exporter settings.

Thus, yes, you do have the chance to join the faces by merging the vertices.

[LechKar_owicz]

Thank you for all the answers. I guess that clears up some things for me. I have now the possibility to test 10.1 environment so I'll definitely look into the Enclose Mulitipatch tool.