Procedural Colosseum

Procedural rules are normally associated with creating detailed 3D models for a large set of data.

CGA (Computer Generated Architecture) rules are also effective in terms of reducing the time it takes to create a detailed landmark (such as the Colosseum) manually. This post shows a simple process and the code that was used to create a quick landmark.


A simple arch and ledge object (.dae) was created in Sketch Up, which was used on the outer level.

Arch collada object from SketchUp

The Colosseum footprint digitized manually as a shapefile from the ArcGIS Imagery basemap.

Oval footprint shapefile

The code with some comments is below:
## Levels attribute serves as a counter, similar as the ## count in a for Method attr levels = 4 Lot--> Go ## The outer level only has an offset of -2, therefore it ## calls the Level Rule with an argument of (-2) Go--> case levels == 4: Level(-2) case levels == 3: Level(-15) case levels == 2: Level(-15) case levels == 1: Level(-15) else: color("#FFC68C") ## The Level rule creates an offset using the argument is ## was called with (x). It then calls the Border_Split rule ## to extrude each level Level(x)--> offset (x) Border_Split Border_Split--> comp(f){border: Extrude| inside: Recursive} ## The Extrude rule extrudes each level 12 (level height) * levels, making ## sure that each ## level's height is reduced by 12. ## Also the first level (a.k.a the outside level) is represented ## differently from the ## other levels, as it will have Arches on the side Extrude--> case levels == 4: extrude (levels*12) Split_First else: extrude (levels*12) Split_Rest ## The recursive rule deducts 1 from the counter and Re-calls the Go rule, ## creating a different extrusion height for each level Recursive--> set(levels, levels - 1) Go ## First (outer) level is divided into the front (which are assigned arch ## geometries) and top sides (tower) Split_First--> comp(f){front: Wall| top: Tower} ## Splits the outer-wall vertically every 12 meters, leaving a 2 meter ## ledge ## at the top. Each split is assigned an arch, while the ledge keeps its ## normal shape Wall--> split(y){{12:Arch}* | 2: Shape} Arch--> i("data/Raw/Arch.dae") r(0, 90, 0) s(scope.sx-0.1, scope.sy-0.1, 5.5) color("#F1B57E") ## The top part of the outer level is split into blocks on the X and Y axes ## and the middle bloch is extruded 5m creating a pole/tower Tower--> split(x){2.6:Shape| 0.2: Tower2| 2.6:Shape} Tower2--> split(y){1: Shape| 0.2:TowerExtrude| 1: Shape} TowerExtrude--> extrude (5) Color ##The remaining levels are colored dark grey on top and light on the sides Split_Rest--> comp(f) {back: DarkColor| top: Color} Color--> color("#514E4D") DarkColor--> color("#F1B57E")



The Result:

Random Tree Generation using 3D Vegetation Library

The 3D Vegetation Models Library from LumenRT is a very user friendly way of creating quick, realistic urban vegetation with a variety of plant species.

The library offers a large variety of trees (some of which I have never used). I wanted the CGA rule to create trees for my shapes at random, from a specified selection. A small alteration to the CGA code changes the default value.

For this example I used the Plant_Loader_with_LumenRT_Models.cga

The Plant_Loader_with_LumenRT_Models.cga uses the Name attribute to determine the file path of the model. The "Alder Buckthorn" model is used as a default. As seen below.

attr Name = 'Alder Buckthorn'

By changing the Name attribute to a conditional attribute, and setting a probability for specified plant models, the CGA rule will automatically assign models to shapes. In the example below, only 20 tree models were specified with a propablity of 5% each.

attr Name = 5%:"Alder Buckthorn" 5%:"American Chestnut" 5%:"American Sycamore" 5%:"Australian Pine" 5%:"Black Locust" 5%:"California Walnut" 5%:"Date Palm" 5%:"Ficus" 5%:"Field Elm" 5%:"Northern Red Oak" 5%:"Red Hickory" 5%:"Sassafras" 5%:"Southern Magnolia" 5%:"Strawberry Tree" 5%:"Sweetgum" 5%:"Umbrella Acacia" 5%:"White Ash" 5%:"White Oak" 5%:"White Poplar" else:"White Willow"

The resulting rule only assigns the models  that were specified as a default. Keeping the original @Range annotation in order to still be able to select any of the other available models.