CUBIZEN: Global Mapper, CityEngine & Creative Tech

Single-file vs Modular CGA Structure

When CGA code becomes too long, you can separate rules by function into modules and reuse them as needed.

This is extremely useful because it is easy to modify and can be reused in other code.

This is a very familiar concept for those who do programming.

For example,

Suppose there are mixed parcels with different uses, and the regulations require changes in building form according to the use, such as through district unit plans.

Writing all the rules for different types of buildings within a single CGA file would result in a massive amount of code, and even with good comments, it remains inconvenient.

This becomes even more inefficient when the file includes building rules that may never be used in certain scenarios.

In such cases, you can save the rules constituting buildings for each use in separate CGA files and then call them for use.

Today, we will look at how import is used through a very simple example.

First, let's look at an example where all rules are included in one CGA.

@Range
attr BD_1_Height = 20
# Height of Building 1

@Color
attr BD_1_color = "#FF0000"
# Color of Building 1

@Range
attr BD_2_Height = 20
# Height of Building 2

@Color
attr BD_2_color = "#00FF00"
# Color of Building 2

Lot -->
    case geometry.area() > 1000:
        extrude(BD_1_Height) color(BD_1_color) X.
    else:
        extrude(BD_2_Height) color(BD_2_color) X.
# If the building area is greater than 1000, attributes of BD_1 are applied; otherwise, attributes of BD_2 are applied.

The above example sets a condition on the building area so that buildings are represented in red if the area is greater than 1000, and green otherwise.

This is the result of the code above. Take note of the Inspector panel shown on the right.

Import-Based Modular Workflow in CityEngine

Now, let's look at an example of separating BD_1 and BD_2 into separate files and importing them.

1st_BD.cga

@Range
attr BD_1_Height = 20
# Height of Building 1

@Color
attr BD_1_color = "#FF0000"
# Color of Building 1

Lot --> extrude(BD_1_Height) color(BD_1_color) X.

2nd_BD.cga

@Range
attr BD_2_Height = 20
# Height of Building 2

@Color
attr BD_2_color = "#00FF00"
# Color of Building 2

Lot --> extrude(BD_2_Height) color(BD_2_color) X.

Once you have saved the rules you want to use as separate CGA files, you create a CGA file that will call these modules.

main.cga

import BD_1 : "1st_BD.cga"
import BD_2 : "2nd_BD.cga"

Lot -->
    case geometry.area() > 1000:
        BD_1.Lot
    else:
        BD_2.Lot

Now, let's look at the result after applying main.cga to the shape.

The attributes of the CGA files called as modules appear separately in the Inspector window.(You can achieve a similar grouping by putting all rules in one file and using annotation functions.)

Although import is not directly related to the interface itself, it is an important concept to understand before diving into CGA coding.

For more detailed information, please refer to the CGA reference regarding import.

Import supports a wide range of advanced syntax options, including style inheritance, independent attribute usage, and rule or attribute overriding.

As the coding content progresses and we reach the point of using import, I plan to cover it by syntax as well.

The time to cover CGA coding is approaching.

Whenever you have time, it will be helpful to look ahead at the code needed for the beginner stage informed in Lesson 17.

Next is the SketchUp extension that allows CGA files to be used in SketchUp.

I intended to cover it, but when I installed the SketchUp trial and checked today, the provided RPK works well, but the RPK I created myself causes a forced termination.

Although I do not actively use SketchUp, I hope the extension continues to receive updates.

I will replace the content about the extension with a link to GitHub.

https://github.com/highered-esricanada/CityEngine-Sketchup-Extension/tree/master