SL Cert - Basic LSL Rotations

This is an initial take on a set of guidelines for scripting position and rotations. It still needs a lot of work and a good deal of thought.

This list of requirements is part of the Second Life Certification project. It is an effort to create a list of specific skills for different topic areas. It is part of a standard to make it easier for people to demonstrate their abilities.

Basic Requirements

In the basic skill sets a person should be able to demonstrate that they understand the basic definitions. The person should also be able to demonstrate that they understand the basic idea. For example, a person should know how to calculate a dot product but also understand its relationship to the idea of a projection of one vector on to another.

Basic definition of position

• Absolute position
• Local position

A person should know what position is in the context of SL. This means the person should know the difference between an absolute position within a sim and the local position within a linkset. An understanding of the different contexts when you might use local versus absolute is vital to working with rotations and vectors. For example, when working within a linkset a local coordinate system is used. At the same time it is not uncommon to make use of local offsets when dealing with two separate objects.

Basic definition of a rotation

• Euler
• Axis and angle
• Quarternions

A person should demonstrate that they know the definitions of a rotation. The person should know the difference between an Euler rotation and a quarternion. A person need not know the specific implementation of a quarternion but should be understand a roation in terms of an axis of rotation and an angle around that axis.

Changing position and rotation via the edit window

A person should be proficient using the edit window to manually move and rotate an object. The person should be able to move and rotate an object to a specific orientation (position and rotation). Also, the person should be able to read the position and rotation for a given object using the edit window.

Vectors and Operations

• Definition of vector in LSL
• Working with vector components (x, y, and z)
• Linear combinations of vectors
• Dot product
• Cross product
• Unit vectors

A person should know the basic mathematical vector operations. The person should know how the calculations are performed and the LSL overloaded operators. For example, given two vectors u and v, the person should know how to calculate the dot product and also know that in LSL u*v will give you the dot product. The person should know how to multiply a scalar and a vector in LSL and add vectors that have been multiplied by a scalar in LSL.

Intermediate Requirements

Reference Frames

• Global
• Local

Basic commands to get position information

• llGetPos
• llGetLocalPos
• llGetRootPosition

Basic commands to get rotation information

• llGetRot
• llGetLocalRot
• llGetRootRotation

Basic commands for changing position

• llSetPos
• llSetPrimitiveParams
• llSetPos within different reference frames.

Basic commands for changing rotation

• llSetRot
• llSetLocalRot
• llSetPrimitiveParams
• How the commands work in different reference frames.
• Rotations
  • Multiplication and division of rotations
  • Difference between left and right multiplication

Working with vectors

• Finding a vector component in a given direction
• Finding a vector perpendicular to two vectors.
• Finding a vector perpindicular to a plane.

Advanced Requirements

Rotations and position

• using llSetPrimitiveParams to move and rotate at the same time
• Rotating and moving a prim to a specified orientation
  • Absolute coordinates
  • Relative coordinates (in a link set)

Smooth movements

Absolute coordinates

• Rotate and movement around the edge of a prim
• Rotate and move around a fixed point
• Rotate and move around a predefined axis

Local coordinates (within a linkset)

• Rotate and movement around the edge of a prim
• Rotate and move around a fixed point
• Rotate and move around a predefined axis

Transitions

• Smooth movements from one orientation (position and rotation) to another.

Determining specific orientations

Absolute coordinates

• Given a point rotate an object to face the point.
• Given two points rotate an object to face perpindicular to the two points.

Local coordinates to local

• Given a point rotate an object to face a local point.
• Given two local points rotate an object to face perpindicular to the two points.

Local coordinates to absolute

• Given a point rotate an object to face a point in absolute coordinates.
• Given two absolute points rotate a local object to face perpindicular to the two points.