## Basic Concepts

Coordinate Axes
Metasequoia's 3D coordinate system is organized as in the diagram on the right. It is a right-handed coordinate system. By default, X is horizontal, Y is vertical, and Z is into and out of the screen. Notice the color coding: X is red, Y is green, and Z is blue.

Document Model
A Metasequoia document holds zero or more objects, and zero or more materials. If you want to edit more than one Metasequoia document at once, start multiple copies of Metasequoia. If you run two copies of the same version of Metasequoia, you can use the Cut, Copy, and Past commands to exchange data between the different documents.

Objects
One document can contain two or more objects. Object panel You can use the object panel to perform "layer"-like operations, where some parts of your document are visible, but inactive, while other parts can be freely edited. Objects are made up of three parts: vertices, edges, and faces. (Abbreviated V, E, and F.) Faces have two sides: a front and a back.. When viewed from the back, a face is not visible. In Metasequoia only triangles and quads are allowed. Faces with more than four edges are not allowed.

Materials
Each face can be assigned a material, and the same material can be assigned to many faces. The Material Property Panel can be used to edit a material's properties (such as its color or texture). Any faces that don't have a material assigned to them automatically get a default material.

Texture mapping and UV values
Texture mapping is used to add realism and/or details to your models. UV coordinates are used to control which part of a texture is mapped to a face. Metasequoia contains several commands which allow you to edit the UV values of an object's faces.
Texture maps can be specified using the Material Property Panel. The texture's data can be edited by using the Paint Panel. In addition, you can edit the texture by drawing directly on the 3D object in the 3D window, by using the Paint command.

World coordinates vs. Screen Coordinates
With some commands, such as the "Movement" command, you can choose which coordinate system to use to perform the command. World coordinates are relative to the scene, no matter how the camera is pointed. Screen coordinates are relative to the camera. You can switch between coordinate systems by pressing the "W" and "S" buttons in the "Edit Option" panel.