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Object vs Shapes

09-17-2018 07:38 AM
Occasional Contributor

Hi people.

Can someone help me understanding what is the difference between objects and shapes? I read the manual but I still can not figure it out exactly.

I have some trouble understanding what is what.

I see there are Object attributes AND shapes attributes. Is it the same thing?

Many thanks


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8 Replies
Esri Regular Contributor

Thank you for your question.

Objects is generic term that comprises (Shapes, Models, Graphs, Terrains, Viewsheds ...)

Some of these Objects like Shapes or Graphs can have Object Attributes.

I hope this clarifies the semantic.

Occasional Contributor

I see! Thanks  Thomas Fuchs

If shapes are a type of object, can I then ask what is the difference between a Object attribute and a Shape Attribute?

Is a shape attribute simply an object attribute of a shape? 

This is the passage from the manual which is confusing me:

"Attributes, Sources and Connections

attributes can have different sources, which allows connecting the values of the attributes in various ways. Sources can be of the types


The value is taken from the corresponding object attribute. The value is displayed in italic, and marked with (Object).


A rule attribute can use a shape source to take its value from the parent shape. For example a street shape may sample the street segment's streetWidth. The value is displayed in italic, and marked with (Shape).


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Esri Regular Contributor

There are Object Attributes and Shape Parameters, there are no Shape Attributes.

The Connection Editor displayed for attribute minArcRadius

Shape parameters define the dynamic shape generated by CityEngine.
Please read the CE help on Creation of Shapes from Graph Networks .

Also Note: Shape Parameters can also be connected to Object Attributes.

Occasional Contributor

Got it!

Thanks Thomas

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Occasional Contributor

Hi Thomas Fuchs . I stumbled into this passage in the manual. Apparently there ARE shape attributes. I am confused again lol 

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Esri Regular Contributor

You are right  in the CGA Language there are Shape Attributes.

These Shape Attributes are properties of current shape the rule is applied on.

The are completely unrelated to the CGA Attributes

attr id = expression

that can be connected to Object Attributes, Shape Parameters and Layer Attributes (see above)

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Occasional Contributor

Hi Thomas Fuchs, let me see if I got it right. To summarise:

OBJECT ATTRIBUTES: properties of a object (static and dynamic shapes, Models, Graphs, Terrains, Viewsheds ...)

LAYER ATTRIBUTES: Every layer can have an arbitrary set of layer attributes defined. Whereas map layers normally use their image data as source for layer attributes, vector data layers can query their vector objects to layer attributes.

SHAPE PARAMETERS: the parameters of blocks, intersections and streets.

SHAPE ATTRIBUTES: properties of the current shape.

BUT.. there seem to be a complication as there is a difference between Initial Shapes and CGA Shapes.


    Shapes are the most important entity within a CityEngine scene. They are the main input for procedural modeling with CGA rules. CGA rules operate on shapes and thus there must be some shape to apply the start rule. Through CGA operations, shapes are modified and finally result in model geometry.

 INITIAL SHAPES ATTRIBUTES: Shapes can reference a set of attributes, including a rule file, a start rule (the first rule that will be applied) as well as a seed to control randomness.

And instead: 


   CGA Shapes are different from the shapes previously mentioned in section Shapes; those shapes are so-called initial shapes.

CGA SHAPE ATTRIBUTES: These attributes contain the numeric and spatial description (including the geometry) of the shape. During the rule application process, these attributes can be accessed and modified by shape operations. The following are the most important shape attributes: Geometry, Scope, Pivot.

So, my question is: considering that both Initial Shapes and CGA shapes exists, what are the 


attributes? CGA Shapes attributes or Initial Shapes attributes, or are they available for BOTH?

AND, if all shapes are objects, are shapes attribute ALSO considered object attributes?

I am trying to make sense of the whole thing, because if I do not I don't think I will be able to understand CE completely. The manual is quite vague and fragmented so I am trying to put everything together. Maybe others have the same doubts I have  and this help 



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Occasional Contributor III

Here a printscreen of my project. There´s a "layer" with 28 objects, but not all the same.

Some objects are Collada Models (.dae file extesion from Trimble Sketchup ). Could be files like.obj, .fbx....

Some others are Shapes with attributes like Type of Space, Area SQM, Floor, building name.... - Shapes where it´s possible to apply Rules  to create 3D models using CityEngine.