Attributes on Start Shapes, such your specific Lot's StreetWidth attributes are constant for the Model since those Attributes are specific INPUTS for CGA to create the Model on this shape.
Once the Model Generation is started, CGA works just with the input it gets.
CGA just executes a series of geometric operations.
Once the Model Generation is started, CGA can not go back and check the environment around the shape and read more info to further process that data in the current Model.
That is currently not possible, but may change with an upcoming release. [same is true with sampled map layer information: it is constant during the Model Generation process.]
Does this also mean that once a generation process starts it can't be interrupted, it has to complete generation and end in a resulting leaf(or error)?
i.e. by the changing of an attribute during the generation process such as streetWidth Attr does it not halt execution and restart the generation? Not that i require this I'm just interested.
What I am not understanding is if I place a list to appear in a UI (@Range) for a shapeNode, for a user to select a streetWidth, for the initialStreetShapeSegment, why the result of this change can not set the attribute on that initialStreetShapeSegment and have it start the regeneration of the initialStreetShape leaf. Yet a map layer can alter this value?
Is there a way to customise per project the attributes and settings on those initialShapes(non user StartShapes)?
I have struggled with this as well. Generally, my way around this was to set the streetWidth attributes in python in GIS then import into CityEngine, but my focus was creating hundreds of cross sections. In a Street Rule, I don't think it is currently possible to have a CGA parameter set a shape parameter (as much as I wish it was possible). In most urban planning use cases it is less annoying because we typically assume we have to keep the ROW constant (so changing sidewalk and street width is a more intentional action).
If your use case is in entertainment, you could write a python script that reacts to your 'width' attribute by setting the streets to match that width. The python examples for setAttribute provide some good code samples. This however would require running your script in the background or when you want to change all your widths. Not great, but a "solution".