Procedural Venice

Venetian buildings are the gems of the history of architecture, attracting researchers to explore the trajectory of style evolution assiduously. Meanwhile, lots of artists also drown themselves in recreating these architectures by various works of art to enhance the sense of immersion and reality. Because of the centuries of development and cultural communication, Venice architecture has formed its unique style, which absorbed the symbolic features of Gothic, Byzantine, Renaissance, and Baroque styles, making it almost impossible to identify only one style on the existing building. These architectural elements collaborate and are always in harmony even they came from very different ages. Maybe that's one of the reasons that in recent years, we have seen many movies and computer games whose settings are in Venice cause a stir, for it usually requires a prodigious amount of work to replicate common Venetian architectures, not to mention the complex palaces and churches.

In this project, to experiment with a more efficient way of creating the rough buildings and even the city by a procedural modeling way, we propose a building pipeline that can handle any shape of footprints and generate a reasonable simple building. It’s noted that manual work on details is still necessary to create a more realistic model. Otherwise, we may get lost in adjusting every little thing while programming the procedural method.

Introduction

Procedural modeling is an umbrella term for several techniques in computer graphics especially in geometry processing to create 3D models by sets of rules. In this project, we are going to randomly generate the Venice building models and provide users with convenient controllers as many as possible using Houdini, with VEX scripts and some visualized nodes. Our project will mainly focus on the shape part of the average building in Venice but not the landmarks which usually require special attention while modeling.

The general pipeline uses a top-down approach and can be extended from each part. The detailed description is as follows:

City generator: creates part of city automatically.

Footprint generator: interprets the OSM data, which contains the geospatial information of the location of Venice buildings, and randomly creates the rough shapes of buildings.

Building generator: decides the distribution of floors and windows for one building, as well as the top-level settings of the accessories.

Roof generator: calculates the shape of roof of the given type and lay roof tiles accordingly. For a flat roof, arrange the distribution and shape of the handrail.

Window generator: assembles a single-window by controlling the parameters of arch, window size, shutters, and fences.

With all generator tools, we can model and iterate the base low-poly building quickly.

Architecture of the procedural Venice

Motivation

The creation of compelling models is a crucial task in the development of successful movies and computer games. However, modeling large three-dimensional environments, such as Venice city, is a very expensive process and can require several years' worth of labor. Fortunately, industries have come up with several procedural modeling methods to speed up the process and Houdini is one of the most popular tools.

In this specific project, most Venetian buildings (except for some landmark buildings such as churches and palaces), can also be automatically generated using the procedural method because from the visual perspective, they share the same construction pattern. Using the procedural generating method will save a lot of work and cost for quickly testing and iteration the scenarios. Another important reason is that the built-in architecture node in Houdini is still in the beta testing phase and only provides very limited parameters. What’s more, it lacks the functions for generating roofs and windows, which are both essential in procedural Venice. We also find that a large number of inner nodes makes the customizing become difficult and slows the cooking speed. So it will help a lot if we can have our generating pipeline.

Project Plan and Milestones

Finished: Finshed as planed

Delayed: Not finished as planed

Changed: Replaced by other method or abandoned

Date	Task
By Week 4	Collect information for the Procedural city generator and GAN painting generator. Prepare for the project kick-out slides.
By Week 5	Discuss with TA the implementation plan of procedurally generated Venice Obtain the original TA's method and engineering files of the procedural Venice. Read books about architecture and start to use Google Maps to classify Venice architecture.
By Week 6	Completed the basic classification of Venetian architecture. Determined the classification of simplified Venetian buildings, palaces, and complex churches. Distinguished and classified various components in simplified Venetian buildings and palaces.
By Week 8	learned the TA's city generator. learned the Houdini Basic operation and programming. Made some basic demos following the tutorial on youtube.
By Week 10	Create simplified building creators using Houdini. Create a basic roof generator. Create city generator with SideFX Labs tools. (We didn't use this method because we think it is difficult to make Venetian style building roof using this method)
By Week 11	Use Maya to build some windows and chimneys, import them in Houdini. Add more details to the basic roof generator( including add vertical roof structure, tiles, chimneys, attic). Solve the problem that the lab OSM node cannot connect to the self-written building generator. Create the basic city generator. Create a basic wall generator, with window models. Create another fence style roof generator.
By Week 12	Improve the building generator, which could adjust building height, windows num etc. Random assign the building height in the city generator. Implement web using Streamlit python package, deep learning method will be used on the web. input to Unreal and make a short video about the final scene (Abandoned because we want to focus on Houdini modeling generator, importing to Unreal might face new conflict and Unreal5 which comes next year will be much more powerful than Unreal4)
By Week 13	Push the models and engineering file to the GitHub. Finish the report. Testing Video (Abandoned because we do not import it into Unreal 4 Engine)
By Week 14	Final Presentation

Node handbook

This part provides the basic descriptions for important nodes and their parameters.

Building generator

Control the total number of floors, resample the footprint outline to decide the distribution of floors and windows, and provide basic information for adding accessories. The parameters are divided into three parts.

Building options: Converts the footprint to a rough building shape.

Parameter	Overview
Number of floors	Decides the number of floors. The max value is 10.
Default height	Controls the default height for each floor. If there is no overriding height for specific floors, it will be used as the floor height.
Default resample	Resamples the edges of the footprint by inner points and adjusts the width for every window unit. If there is no overriding resample value for specific floors, it will be used as the resample value.

Window options: Sets the concrete position of window units.

Parameter	Overview
Default position	The vertical distance from the window bottom to the floor. If there is no overriding value for specific floors, it will be used as default.
Default window height	Default height of the window placeholders. This value may differ from the actual height of the window models.
Default window width	Default width of the window placeholders. This value may differ from the actual width of the window models.

Details: Applies overriding control over specific floors.

Parameter	Overview
Floor index	The floor needs to be modified.
Height	Rewrites the height of the floors.
Resample length	Rewrites the resample value of the floors.
Window options - Position	Rewrites the window position of the floors.
Window options - Height	Rewrites the window height of the floors.
Window options - Width	Rewrites the window width of the floors.

Roof generator

Constructs a hip/gable/flat roof by the given type and distributes tiles automatically. For the hip/gable roof, only external corners will be covered by tiles.

Parameter	Overview
Expansion	Expands the footprint of the roof from the base footprints.
Roof type	Switches among hip/gable/flat roof types.

Notice that it may take a while to generate a single hip or gable roof because of the boolean operation on tiles.

Fence generator

Creates a fence on the given polyline. This node is automatically called while generating the flat roof.

Parameter	Overview
Resample	Controls the subdivision level of the pillars. Smaller value gives preciser controls over the pillar shapes.
Length	Controls the length of the pillars.
Common pillars	Controls the curve and thickness of the common pillars that are on the middle of polyline segments.
Special pillars	Controls the shapes of special pillars that are on the ends of polyline segments.
Fence	Controls the shapes of fence.

Ledge generator

Creates continuous or separated ledges on the given polyline.

Ledge decoration generator

Window generator

Methodology

Classification of Venetian buildings

Correctly classifying Venetian buildings is very important in this project. Using Google map of Venice, pictures on Google, we classify Venetian buildings into 3 types, which are churches, simplified normal buildings, and palaces (as the pictures below). For churches and palaces, due to their sophisticated design, they have more features and types than simplified normal buildings. Especially for churches, because of its uniqueness, procedural modeling is of little significance compared to manually modeling. After considering the technical difficulties and workload, we decided to focus on simplified Venetian buildings.

Venetian building types:

Churches (Need to model manually because of the uniqueness of the church)

Different types of churches in Venice

Palaces

Different types of palaces in Venice

Simplified buildings

Different types of simplified buildings in Venice

We can see that compared with palaces, simplified buildings have regular cubic shapes. The roofs are mostly sloping roofs with chimneys. The windows are simpler than palaces, and there are fewer windows with carved rails. Simplified Venetian style buildings has different components. We can classify them through texture(color, wall damages), chimneys, windows, doors.

Different component types:

Windows

Different types of windows in Venice

Chimneys

Different types of chimneys in Venice

Roofs

Different types of roofs in Venice

Roof generator

Two Roof types

roof generator type 1
roof generator type 2

Roof details

We used the 3D modeling software Maya to build some chimney models and exported the FBX file to Houdini. A certain density of points can be randomly generated on the plane of the roof of the house so that the chimney with the normal upward is assisted on the corresponding point.

chimney model 1	chimney model 2

Window generator

For the window generator, in the actual project, we did it in two methods at the same time:

One is to use the Maya modeling software to model the Venetian windows then import it into the Houdini engine. The advantage of this method is that it is relatively straightforward and we can use the Maya for complex window structures. However, the disadvantage is that there are not many variables that can be programmed and automatically controlled.

Window model 1	Window model 2	Window model 3	Window model 4	Window model 5

Another method is to use Houdini to program the windows. We chose the arched window structure to generate it, using the tangent relationship of the circle to generate a total of 7 types of arched structures. But due to the time limitation, we did not finish the whole window structure.

Window generator type 1	Window generator type 2	Window generator type 3	Window generator type 4
Window generator type 5	Window generator type 6	Window generator type 7

Simplified Building model

Compared with Houdini's original Building generator, our building generator has a simpler structure and at the same time increases the control of the roof shape, which can better fit the roof shape of Venice.

simplified building generator

Venice city generator

OpenStreetMap of Venice is used as a reference to pinpoint the location of every building. Using the sideFX Labs tools, the Venice city buildings' locations could be pinpointed in Houdini, and the street information and building inner parts are filtered using OSM filter node. Because there are some overlaps between different surfaces, so we add a boolean node and union the overlap surfaces.

Venice OSM data

In this step, we connect the OSM data to our building generators. First, we traverse all OSM surfaces and use each OSM surface as the bottom surface to reconstruct the building generator. All OSM surfaces are separated into individual small surface, and a single building is generated on the small surface specifically, the height of the building and the height of the roof bottom are given the same random height.

Bird view of Venice
Bird view of Venice
Different height of houses

Quality Assessment

Roof generator assessment

We have made two types of roof generators. For different shapes of ground, our roof generator can automatically generate the corresponding shape of the roof.

It can be seen that for a single roof, the roof can be automatically covered with tiles if the amount of computer calculation allows. On the roof of Venice, there are tiles neatly arranged on the roof, but due to the age, some tiles have faded and some degree of damage has also appeared.

real Venice roof
roof generator model

Among the buildings in Venice, a very small part of the roofs (mostly on the riverside) are fence-style. You can compare the following two pictures. Our second roof generator restores this type of roof style.

real fence roofs
roof details model

We can see that the roofs of Venice show irregular shapes. The roofs are vertical and inclined, but in our city generator, there are only inclined ones. That is because our vertical roof structure has some bugs when dealing with a large number of irregular models. So we commented it out temporarily. It can be seen that the effect of our roof generator results in fitting irregular roofs is very close to the real situation.

real roofs
roofs' model
Rendered roofs

We compared the top view of the roof near San Giacomo di Rialto in the real Venice with roofs generated by our roof generator, and found that from the top view, the shape and style of the roof are basically similar to the real Venice(the green box parts below). But if you look carefully, there will be some differences, for example, if there is an open space in the middle of the building, this area may be filled in the generated model(the red box below). At the same time, the roof will also have some randomly generated structures, just like the strange structures that would appear in real Venice.

Comparation of roofs near San Giacomo di Rialto from the top
Rendered roofs from the top

Building generator assessment

we used the building generator randomly generating two buildings for assessment, with different types of windows and roofs.

For buildings near the river, there will be a small number of fence-type roof buildings. When classifying, we classify them as palaces. In our single building generator, this type of building can be reproduced well. The disadvantage is that there are still some details missing, such as flower pots outside the windows, corner decorations, etc., which can be attached to the building generator in the same way as windows.

Simplified Building 1
Simplified Building 1
Simplified Building 2

For simple buildings, which are also the buildings with the most in Venice, we can see that our randomly generated buildings can also reproduce this type of building. We can control the number of windows on each floor, the height of each floor, the total number of floors. However, it has the same drawbacks as the last one: in a real Venetian architecture, there will be many details, such as clothes poles, telephone poles, etc., which need to be constantly improved to look more real. Compared to the real Venice, our generated models are still too clean, too neat, and lack traces of years.

Simplified Building 3
Simplified Building 3
Simplified Building 4
Simplified Building 5

City generator assessment

We used Houdini to generate 1,407 buildings in the central area of Venice. Compared with Google Maps 3D, from the perspective of a bird's-eye view, we can see that the generated city are very similar to Google 3D map.

Real venice city from Google Map 3D
Generated venice city in Houdini
Rendered venice city in Houdini(white model)

Limitation

Running time limitation

For procedurally generated roof with tiles, if all building tiles in the city are generated procedurally, it will cost a lot of computing time and resources. For a tile, there are more than 10 faces, and it takes much time to generate a roof covered with such tiles using Houdini(with GTX1060). Our test city OSM scene has 153 building planes, which is quite small compared to the real size of Venice. If we generate all the roofs covered with tiles, then it will definitely take hours or even days. We think Applying UV mapping to the roof can be an alternative method to deal with the roof tiles.

Archetecture Precision limitation

At present, the procedural generation of Venetian buildings can only correspond to the bottom contour of the building. However, it cannot automatically match the number of building windows, window styles, roof shapes, and other factors of the buildings. We have not build a connection with data points or pictures of Venice, which is very difficult in Houdini engineer.

Dilapidated

We did not think about the dilapidated problem when we actually modeled. Actually, many tiles in Venice buildings are damaged, many walls are worn, many bricks are missing, and many chimneys are damaged. The houses we generated are too clean, too tidy, no clothesline, no flower baskets, no breath of life, and lack of traces of yeas.

Github Link

Procedural-Venice

References

Literatures

[1] Tavakkol, Sasan & Han, Feng & Mayer, Brandon & Phillips, Mark & Shahabi, Cyrus & Chiang, Yao-Yi & Kiveris, Raimondas. (2020). Kartta Labs: Collaborative Time Travel.

[2] Răzvan, Cristea. (2020). Procedural Generation of Architecture & Props.

[3] A history of world architecture (before the end of 19th century), in Chinese.

[4] Procedural Modeling of Buildings. Article in ACM Transactions on Graphics · July 2006