What are FreeCAD's coordinate systems?

Contents

  • 00:00 Introduction
  • 01:12 Explanation of 3D space
  • 03:09 Simple explanation of planes
  • 03:53 FreeCAD's basic planes
  • 05:35 Local coordinates
  • 06:37 Placement and Attachments points

FreeCAD like all CADD systems uses a coordinate system that provides a basis for defining all objects in the model. Some CADD systems use a two dimensional (2D) coordinate system which only allows you to draw in two dimensions, while other systems use a three dimensional (3D) coordinate system that allows objects to be drawn in three dimensions. FreeCAD uses a three dimensional coordinate system.

Types of coordinate systems

FreeCAD has a global coordinate system that defines the entire universe that a FreeCAD model can utilise. You can place objects anywhere within that space. This coordinate system is used by the Draft Workbench and the Part Workbench.

FreeCAD's Part Design Workbench also has the concept of a local coordinate system. A local coordinate system is similar but different to the global coordinate system. We'll expand on this a little further on in the article.

What is the Global coordinate system?

The global coordinate system defines the entire 3D model. When viewed from the front of the model, the:

  • x-axis runs left to right horizontally;
  • the z-axis runs up and down vertically;
  • and the y-axis runs in and out of the screen;

Every object in a FreeCAD model has a placement point in the global coordinate system. The placement point is the object's origin point. You are manipulating the object's origin directly when you manipulate the placement point.

Note

FreeCAD's Part Design Workbench has the concept of an attachment point which is different to the placement point. This will be explained later in the article.

Workbenches such as the Draft Workbench and Part Workbench create objects that only have a placement point. You can move these objects by manipulating the placement point which is in the global coordinate system.

What is the Local coordinate system?

The local coordinate system is a coordinate system that is attached to a specific feature in the Part Design Workbench. They differ from an object using the global coordinate system which is not attached to anything else. They are specific to the Part Design Workbench.

Important

The major difference between the local coordinate system and the global coordinate system is the direction of the axes. In the local coordinate system the:

  • x-axis runs left to right horizontally;
  • the y-axis runs up and down vertically;
  • and the z-axis runs in and out of the screen;

Changing the values of the attachement point in the local coordinate system changes the offset from the placement point and moving the feature in the global coordinate system.

A feature that has a Local coordinate systems has been attached to another feature and also has what's known as an attachment point. The attachement point should be considered as an offset to the feature's placement point.