[018] How to Convert Models to Shapes and Fix Perspective Distortion in Esri CityEngine

Transition from dynamic procedural models to editable static geometry and prepare clean, distortion-free facade textures.

In this Esri CityEngine tutorial, we conclude our look at the Shape menu by exploring two vital tools: Convert Models to Shapes and Crop Image. These functions allow you to "freeze" procedural results for manual editing and correct perspective issues in real-world building photography.

    Convert Models to Shapes: Transitioning to Static Geometry

    The Convert Models to Shapes function is used to transform a 3D model generated by a CGA rule—or an imported 3D object—back into an editable Shape. When a building is in its "model" state, it is actively driven by a Rule File and a Start Rule.

    [img 1 : Model status with active Rule File and Start Rule]
    [img 1 : Model status with active Rule File and Start Rule]

    After applying Convert Models to Shapes, the Rule File and Start Rule fields in the Inspector will become blank. This indicates that the procedural logic has been "baked" into the geometry, and the model has returned to a Shape state where new rules can be assigned.

    [img 2 : Empty rule fields after conversion to Shape]
    [img 2 : Empty rule fields after conversion to Shape]

    Once converted, the result of the previous rule remains as static geometry. By default, the polygons might be joined into a single shape. If you need to apply different rules to individual parts of this model, you can use the Separate Faces command.

    Refining Geometry with Separate Faces

    In the example above, 8 shapes are initially joined as one. By selecting the object and running Shape - Separate Faces, you can isolate every polygon, allowing for granular control and independent rule application for each face.

    [img 3 : Using Separate Faces to isolate polygons]
    [img 3 : Using Separate Faces to isolate polygons]

    Crop Image: Fixing Perspective for Facade Textures

    Video : how to correct architectural perspective distortion

    The Crop Image tool is essential for preparing building textures for the [013] How to Use Facade Wizard in Esri CityEngine for Procedural Facades Building facades should ideally be perfectly rectangular. However, photos taken from ground level often show the upper floors shrinking due to "keystone" perspective distortion.

    Crop Image allows you to manually correct this perspective distortion. By defining the four corners of a facade, you can flatten and crop the image into a clean orthophoto suitable for 3D modeling and high-quality texturing. 

    Practical Usage Tips

    When using the Crop Image tool, ensure you zoom in to select corners precisely. A clean crop leads to better tiling and more realistic procedural facade generation. This simple manual fix saves hours of external editing in Photoshop.

    What's Next?

    We have now completed our overview of the essential Shape menu tools. In the next session, we will explore how to extract real-time data from your models:

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    Modern architecture is the correct and magnificent play of masses brought together in light. To master the digital twin, one must first learn to freeze the logic of the rule into the reality of the shape.

    — Urban Designer

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