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CityEngine - Mesh Merging/StaticMeshActor/"Pivot" Actor Inconsistencies

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    CityEngine - Mesh Merging/StaticMeshActor/"Pivot" Actor Inconsistencies

    I have been working with CityEngine/Datasmith/Unreal, trying to find optimal export settings that are optimal to my workflow. Right now the export settings are giving me mixed results – specifically the mesh merging. I think I can rewrite my CGA to work around it, but what is not clear is when CityEngine/datasmith creates a new actor or merges a mesh. The “pivot” actor adds a whole other layer of complexity but I think I can work around that.

    Here is a CityEngine Screencap.

    The buildings in the foreground are what I call detailed buildings - where I generate architectural details inside my CGA code in CityEngine. Things like walls, windows, parapets, awnings, etc...
    Buildings in the background are real simple - a textured box essentially. I am not having any issues with those. I'll explain below.

    ​​Unreal/Datasmith - Export Settings: Mesh Merging: Initial Shape, Instancing: Disabled.
    The accuracy of the models are correct and the mesh/merch is perfect. However, the problem with this approach is that I would like to replace static meshes - like these simple trees - inside of Unreal. This approach does not allow me to do that. The Static Mesh is merged at the CityEngine shape - in my case the parcel.

    Unreal/Datasmith - Export Settings: Mesh Merging: Initial Shape, Instancing: Use Instancing
    This approach gives me the ability to replace static meshes of trees and cars and things, but the instancing I have noticed, creates instances of my "Walls" in my CGA and the accuracy of the placement is not always accurate. So I am getting these big gaps in my buildings - where instances are not being placed with 100% accuracy. Another thing I've noticed is that the "pivot" actor created for the group/shape is placed at 0,0 for every shape or parcel. Working with a model of an entire city...this is pretty difficult.

    I suppose it would be helpful to know why there are inaccuracies with the placement of the instancing, or perhaps ever better, when CGA creates a new instance or object.

    The City Engine datasmith exporter is coded and maintained by ESRI. I will try to bring your issue to their attention as I don't think they monitor actively this forum
    Pierre-Felix Breton

    Sr Technical Product Manager AEC, Unreal Engine Enterprise
    Epic Games - LinkedIn

    Unreal Studio Documentation
    Unreal Studio Technical Support
    Report Unreal Studio Bugs


      Thanks Pierre - I've been in contact with their staff and evidently they do check up on this from time to time so that's reassuring. I'll be sure to post my solution to leave a trail of help for anyone else here.



        Hello, I have exactly the same problem... for me this happens for objects that are placed in the CityEngine with the insert method. For me, this looks like numerical instabilities as I'm using a geo-referenced coordinate system and, thus, having quite large pivot coordinates.

        Is there any news on this topic?


          Sorry about the silence on this - we're looking into it.



            I'm looking into the issue. Would it be possible to send us the scene you encountered the issue with?



              Better late than never: CityEngine 2019.1 will have a fix for this (exporting instances which are located at large GIS coordinates had a precision issue).