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Shapes, Models and Model Export

Question asked by MBuehler-esristaff Employee on Nov 1, 2012
Dear CE community

I've seen that there are quite a few users for whom some concepts of the model creation are still unclear. :) So let me explain the main concepts behind 'Shapes', 'Models' and 'Model Export'.

Please have a look at the attached scheme image.

Notes about the scheme :
1] CityEngine is a procedural modeling application, thus the 'result' of working with CityEngine is a '3D Model'.
2] 1 'Shape' + 1 'CGA Rule File' (+assets/textures) --> Model Generation --> 1 'Model'
3] Assets can also be placed in the scene as so-called 'Static Models', which themselves represent already a final 'Model' and have no more need for being processed with CGA. (Static Models have no 'Rule File' and 'Start Rule' slots in the Inspector)
4] Both 'CGA generated Models' and imported 'Static Models' can be CONVERTED to Shapes for further processing with CGA (dashed line in the scheme).
5] Shapes by default are not textured, e.g. if you draw them manually with the 'Polygonal Shape Modeling Tool' (CE 2012 and later). But Shapes can also have textures as a result from importing a textured asset as 'Shapes'. Or Shapes can be textured with the 'Shape Texturing Tool' (CE 2012 and later).
6] --> both 'Shapes' and 'textured Shapes' are - conceptually spoken - not 'Models', even if they look as such in the viewport.
7] If you want to explicitily generate a 'Model' from a Shape within CE, you have to use a CGA rule file. For a simple conversion, the following CGA code already suffices (which you have to attach to the rule, then generate):
Shape --> MyModel.

This simply copies the incoming shape plus it's textures in a simple final 'Model'.
8] Nevertheless, you can also export Shapes which have NO RULE ASSIGNED as Models, as if they were Models. It is important to understand that this is the default behavior in the Export settings which just exports the shapes. Check the attached screenshot with the export settings. You'll notice an option where Shapes without assigned rules can also be ignored instead of exporting their basic Shape geometry.

--> Make sure on what type of geometry you are working.
Shapes �?� Models !

Hope this gave some insight. :o

Cheers !