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Building a world

This tutorial describes the process of creating a world with both static and dynamic objects.

Terminology

World: The term used to describe a collection of robots and objects (such as buildings, tables, and lights), and global parameters including the sky, ambient light, and physics properties.
Static: Entities marked as static (those having the <static>true</static> element in SDF), are objects which only have collision geometry. All objects which are not meant to move should be marked as static, which is a performance enhancement.
Dynamic: Entities marked as dynamic (either missing the <static> element or setting false in SDF), are objects which have both inertia and a collision geometry.

Setup

Make sure Gazebo is installed.
Start up gazebo, and you should see a world with just a ground plane.
```
$ gazebo
```

Adding Objects

Gazebo provides two mechanisms for adding objects to Gazebo.

The first is a set of simple shapes, located above the render window.
The second is via the model database, which is accessible by selecting the Insert tab in the upper left corner.

Adding Simple Shapes

Boxes, spheres, and cylinders may be added to the world by clicking on the appropriate icon above the render window. Each shape is of unit size:

Box: 1x1x1 meter
Sphere: 1 meter diameter
Cylinder: 1 meter diameter, 1 meter length

Select the box icon, and then move your mouse onto the render window. You will see a box that moves with your mouse. Left click when you are happy with the position of the box.

Repeat the same procedure for the sphere and cylinder. You should end with a world similar to this:

Adding Model from the Model Database

Gazebo's model database is a repository of all types of models including robots, tables, and building.

Select the Insert tab in the upper left hand corner to access the model database.

The list of models are divided into sections according to their current location. Each section is labeled with a path or URI. Selecting an object located on a remote server will cause the model to be downloaded and stored in ~/.gazebo/models.
Try adding various models to the world. Be patient when downloading models, as some may be large.
You should end up with something similar to the following, depending on the models you decided to add:

Position Models

The pose of each model may be altered through the translate and rotate tools:

Translation

The translate tool allows you to move the object along the x, y, and z axes. Select this tool now (or press t) and click on the object you want to move. A three axes visual marker will appear over the object, which allows you to move the object in x, y, and z directions.

You can also just click on the object itself and drag it to move on the x-y plane. You may control which axis the object moves along by pressing and holding the x, y, or z key while dragging the object.
You can hold the Ctrl key to snap the movement to a 1 meter grid.
If the object is not aligned with the world (for example after you use the rotate tool explained next), you can hold the Shift key so the visual markers show up aligned with the world, and you can translate in world coordinates.

Try moving the objects around now into a different configuration.

Rotation

The rotate tool allows you to orient a model around the x, y, and z axes. Select this tool now (or press r) and click on the object you want to move. Three ring-shaped visual marker will appear over the object, which allows you to rotate the object around the x, y, and z axes.

You can also just click on the object itself and hold the x, y, or z keys while dragging it to constrain the motion to one of these axes.
You can hold the Ctrl key to snap the movement to 45 degree increments.
If the object is not aligned with the world, you can hold the Shift key so the visual markers show up aligned with the world, and you can rotate about the world axes.

Try rotating the objects into a different configuration.

Scale

The scale tool allows you to resize a model in the x, y, and z directions. Currently the scale tool only works with simple shapes, i.e. box, cylinder and sphere. Select this tool now (or press s) and click on a simple shape. A three axes visual marker will appear over the object, which allows you to scale the x, y, and z dimensions of the object.

You can also just click on the object itself and hold the x, y, or z keys while dragging it to constrain the scaling to one of these axes.
You can hold the Ctrl key to scale in 1 meter increments.

Try scaling the simple shapes into different sizes.

Delete Models

Models may also be deleted by selecting them and the hitting the Delete key, or by right-clicking on a model and selecting Delete.

Try deleting a few models.

Saving a World.

Once you are happy with a world it can be save through the File menu.

Select the File menu now, and choose Save World As.

A pop-up will appear asking you to enter a new filename. Enter my_world.sdf and click okay.

Loading a World

A saved world may be loaded on the command line:

gazebo my_world.sdf

The filename must be in the current working directory, or you must specify the complete path.

Next: Modifying a world tutorial