AutoCAD Lesson 10 Introduction
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Any position in space can be specified in terms of its distance from a fixed point in the x, y, z directions.
But Einstein tells us that everything is relative. So the question is does "Everything" include virtually everything or only literaly everything. Is our virtual 3D CAD space relative or absolute, and if the former, relative to what.
Happily AutoCAD gives us the best of both worlds:
- Absolute Co-ordinates
- Relative Co-ordinates
Absolute Co-Ordinate System
Every Drawing is supplied with a World Co-ordinate System (WCS). This is
a reference co-ordinate system against which all others can be compared.
This is essential to allow different drawings/models to be combined or
compared.
Relative Co-Ordinate Systems
The WCS on its own would be very restrictrive. To have to specify all
locations against a fixed co-ordinate system would be almoost impossible
for any models involving inclined planes at odd angles.
What would be much more useful, would be to create new/temporary
co-ordinate systems to locate objects. These are caled User Co-ordinate
Systems (UCS), and can be defined in numerous different ways. Control
of the UCS is essential to taking control of 3D space. It is important
to realise that without the WCS, UCS could not exist, the refernece is
is necessary to be able to relate the various UCS to each other.
This tutorial is the copyright of J. Attree
South Bank University, London UK