3DVeniceBridges

Introduction

Venice is built on a group of 118 small islands that are separated by canals and linked by over 400 bridges. Venice is built on a group of 118 small islands that are separated by canals and linked by over 400 bridges. The Bridge plays such an important part in Venice that studying the bridge can help us understand better the history and structure of Venice. Our project is mainly based on the book Catalogo Veneziano – Ponti Santa Croce and Catalogo Veneziano – Ponti San Polo, to build specific 3D models for these bridges and to create specific additional layers on the geographical information system.

The bridges of Venice

Motivation

With more than 400 bridges, Venice is known as the “city of bridges”. In fact, the evidence of the first stone bridges dates back to 1170, and before that time people only used boats to go from one of the 121 islands to another island. Because of technological progress, population growth, and the city’s increase in trade it became necessary to build routes that would connect the various areas. That is how the bridges of Venice were born.

Bridges are an integral part of Venice. The bridge connected Venice from a number of scattered islands into a whole, facilitating economic and cultural exchanges and development within the city, while the economic and cultural development also contributed to the construction of the bridges. The construction of bridges’ 3D models allows us to understand more about the structure and history of the city. What’s more, digitalizing this information allows the researchers to carry out further analyses.

Our project is based on the materials (Catalog Venezia), combined with today's bridge photo, to upgrade the Napoleonic cadaster with bridge information. Given the huge number of bridges in Venice, it would take a long time to build each bridge manually. We have found that the majority of the bridges mentioned in the materials are composed of 4 parts: arc, plane, stairs, and railings. And different parts have different types. So we want to create a bridge generator in which we can specify the type and data of each component based on the materials to build the 3D model for bridges of Venice.

Methodology

1. Build Database

1.1 Classify the Bridge

Before building the 3D model, we need to figure out the typologies of bridges. To facilitate 3D modeling, we treat the bridge as four parts: arc, bridge body, stairs, and railings. Different parts have different types, which form a wide variety of bridges.

1.1.1 Arc

There are two main types of bridges in Venice, arch bridges and girder bridges：

1. Non-arched bridges are referred to as girder bridges, also called truss bridges. Truss bridges generally have a horizontal deck between two imposts and therefore require longer access ramps than arch bridges, whose ramps are inclined from the keystone to the abutments; in addition, generally speaking, girder bridges need to have higher structural depth than arch bridges. Against these disadvantages, truss bridges have the undoubted advantage of generating mainly vertical reactions on the foundations, making them highly suitable for the city’s soil characteristics.
2. Arch bridges are much more prevalent, as they successfully integrate the need for a continuous pedestrian walkway with the need to leave sufficient space underneath for boats to pass. Arches are designed according to various formal types: semi-circular, horseshoe, segmental, equilateral pointed, elliptical.
   • (a) Round, when the curve of the arch is equal to a semi-circumference (fig. 1): tutto sesto.
   • (b) Curved, when the curve of the arch is greater than a semi-circumference (fig. 2):sesto rialato.
   • (c) Normal, when it is a low-slung arch, cod with the curve smaller than a semi-circumference (fig. 3): normale.
   • (d) Only if the curve is smaller than a semi-circumference is the arch called a low arch (fig. 4)sesto ribassato.
   • (e) Equilateral pointed(fig 5):acuto o gotico.
   • (f) Polycentric, when the curve results from the union of several (3 or 5) arcs of circles of different radii (fig. 6): policentrico.

Different types of arcs

3_pionts_circle

We found that most of the bridges from the materials are type c and type d, and very few bridges of type e and f. Thus, we can draw the arc using “3 points” ways to build the 3D model for most bridges.

1.1.2 Bridge Body

According to the books “I ponti di Venezia” there are three types of bridges material:

1. Wooden bridges (Struttura in legno ).
2. Stone bridges (struttura in pietra d'Istria / struttura in pietra).
3. Iron bridges (struttura in ferro).

Wooden bridge

Stone bridge

Iron bridge

1.1.3 Stairs

Staircases are generally the straight flight of stairs, with some differences in shape the shape of the step. There are two different types of step’s shape:

1. Normal Rectangle.
2. Normal Rectangle with an arc in the corner.

normal stair

circle stair

1.1.4 Railing

According to the book “I ponti di Venezia” there are two types of railing material:

1. Iron railings (spallette in ferro).

   All metal handrails are composed of balusters, which differ in their shape.

2. Stone railings (spallette in pietra).

   There are two types of railings made of stone; one is composed of balustrade, the other is solid railings.

Iron railing

Stone railing with balustrade

Stone railing with solid railing

1.2 Digitalize and OCR the Materials

First, we digitalize the materials (Catalog Venezia) with printers to get the ‘.pdf’ file. Then, we use OCR to recognize the descriptive text information from the scanned pdf file. As for recognizing results, we first delete the messy code and then manually check and correct the results to get our final information.

1.3 Organize the Collected Data and Build Database

1.3.1 Description Data

The information that we got from OCR pdf file is descriptive text information, which tells us the information of name, location, and types of bridges.

Parameter	Description	Usage
id	The unique id of each bridge	--
name	The name of the bridge	--
river	The river which the bridge crosses	Update GIS information
street	The street connected by this bridge	Update GIS information
district	The community where the bridge is located	Update GIS information
structure	The type of the arc. ‘0’ is the flat bridge, ‘1’ to ‘6’ are six types of arch bridges, and these six tags correspond to the categories in section 1.1.1	Build the arc model
material	The material of the bridge body ‘1’ is the wooden bridge, ‘2’ is the stone bridge, ‘3’ is the iron bridge,	Do the texture mapping
railing	The type of the bridge railings ‘2’ is the stone railing, ‘3’ is the metal railing	Build the railing model

1.3.2 Measurement Data

In order to build the 3D model based on the plan of the bridge provided in the material, we need to get some length parameters of the bridges in the plan. We import the plan into Rhino to take measurements and get the following data:

Parameter	Description	Usage
river width	--	The width of the arc
bridge length	--	Build the bridge body model
bridge width	--	Build the bridge body model
stair number	The number of steps (left and right)	Build the stair model
stair tread	The tread (length) of each step	Build the stair model
railing width	--	Build the railing model
elevation difference	The height difference between left landing and right landing	Build arc and bridge body model

Using the data above, we can calculate other data like the width of stairs (bridge width - 2 * railing width).

1.3.3 Data to Be Speculated

There are still some data we cannot get from the materials, and we need to speculate these data with our common knowledge and the photographs of these bridges.

Parameter	How to speculate
step riser	According to the relation between riser and tread we can get an approximate value of the riser.
bridge height	Calculate the height of the bridge based on the height and number of the step.
arc height	The approximate range of the arc height can be obtained from the type of arc, while the height of the arc is less than the height of the bridge. Based on these 2 conditions, we can estimate a suitable value.
railing height	Estimate height of railing based on real pictures

2. Build 3D Model

2.1 Build A General Bridge Model

We first build a simple and general bridge model to better understand the whole structure of the bridge and the relationship between the components.

2.2 Build Models of Different Components

We create 3D models of the four components separately according to the previous classification.

2.2.1 Arc Model

Since most of the bridges are type c and type d, we use the way that creates a circle depending on 3 points to build the arc model. We have one arc model and one flat model.

2.2.2 Bridge Body Model

The difference between different types of bridge body is the material. So we make three types of texture mapping on the bridge body according to the bridge’s material.

2.2.3 Stairs Model

Staircases are generally the straight flight of stairs, and the shape of the step is mainly a normal rectangle. So we create one type of stair and modify it according to the parameters. There could be multiple staircases on the bridge, and we can adjust the parameters and create multiple staircases according to the specific bridge.

Multiple stairs

As for the special shape of the step which is a rectangle with an arc in the corner, since there are not many of them, we will treat them as special cases to be improved at a later stage.

2.2.4 Railing Model

We build two types of railing models, one is solid railing and the other is railing with balustrade. And then we make texture mapping according to their railing materials.

2.3 Input Parameters into 3D Model

We import the plane into Rhino, measure the length of the bridge, and store the data in the component in the grasshopper. Then we connect these components with the model, i.e. the parameters are passed into the model. So we can generate the 3D model of bridges semi-automatically.

Project Plan and Milestones

Milestones

1. Initial research on Venice Bridge: books and other materials, work on general methods. ✓

2. Classification of the Bridge: common and special features. ✓

3. Determination of relevant parameters: description, measurement and speculation. ✓

4. Digitalization of the books: formation of structured data. ✓

5. Preliminary model: simple bridge structure. ✓

6. Modular design: implementation of different components of the bridges

7. Parameters input: create models for common bridges

8. Adjustment on special bridges

Project Plan

Date	Task	Completion
By Week 3	Brainstorm projects ideas Prepare slides for initial project idea presentation.	✓
By Week 4 - 5	Discuss the implementation of 3D bridges modelling with TA, and figure out specific steps to achieve Learn about classification and the basic structure of Venice bridges. Learn to use Rhino and Grasshopper	✓
By Week 6	Learn to use Rhino and grasshopper Digitalize the material "CATALOGO VENEZIANO-PONTI" Find the parameters that are needed for modeling and build the framework of the database	✓
By Week 7	Build a simple and standard bridge model	✓
By Week 8	Build the arc and bridge body model Find out a method to measure the length of bridges on the materials	✓
By Week 9	Get the information from the material using OCR Build the stair model Get the length data from the plan using Rhino	✓
By Week 10	Build the railing model Write the introduction, motivation, and project plan on wiki Prepare slides for midterm presentation.
By Week 11	Complete different railing model Add texture mapping to the bridge according to its material Finish the 3D bridge model
By Week 12	Input the data and types of bridges to the 3D bridge model, and generate the 3D models of bridges.
By Week 13	Complete the wiki on motivation, methods, results, and limitations. Build and refine some special bridge models
By Week 14	Final presentation

Limitation

1. 部分信息缺失 2. 图片 Precision limitation 3. 不是1808年的信息 4. 桥的细节没有完全一样

Future work

1. 去获得更具体的信息 2. 细节建模和材质渲染 3. 研究1808年的桥到底啥样 4. 探索新的建模方式

References

Literatures

• STUDIO SAÒR. (2018). Catalogo veneziano.
• RIZZO, T. (1983). I Ponti di Venezia. Roma, Newton Compton.
• de miranda, Mario & Pogacnik, Marco & Skansi, Luka. (2010). Bridges in Venice - Architectural and Structural Engineering Aspects. IABSE Symposium Report. 97. 88-95.10.2749/222137810796063841.