gifTarget Mechanism Overview

The “Target” mechanism allows you to apply modelling operations on two different “Target” lattices: A and B, each of which has Primal and Dual quad-edge manifold.

Setting the Target

Set the target on the Toolbar using the Target choice pop-up menu:

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When the target is set to ‘Target A’, all operations apply to Primal_A and Dual_A. Conversely, when the target is set to ‘Target B’, all operations apply to Primal_B and Dual_B. When you change to a specific target it is automatically made visible. You can hide or show a target by checking/unchecking its entry in the ‘View’ menu.

Whenever the target is changed, the title bars of all relevant windows update to show the current target. For example, the title of the Attributes window shows either ‘Target A’ or ‘Target B’.

Target Mechanism Purpose

The purpose of the target mechanism is to allow the creation of spaceframes that span between the manifolds of ‘Target A’ and ‘Target B’. Each vertex, edge and face in a manifold is assigned a QE_ID (quad-edge ID). Providing that subdivision types and frequencies match between targets, the QE_IDs in ‘Target A’ will match the QE_IDs in ‘Target B’. Thus a vertex in the Primal manifold of ‘Target A’ can be joined to its twin vertex in the Primal manifold of ‘Target B’. Further, the duality inherent in the quad-edge data structure means that a Primal vertex can also be linked with its Dual face and vice-versa – and this dual linkage extends between targets. For example, you can create trifans in the Primal faces of ‘Target A’, and then project the trifan centroids to the corresponding Dual vertices of ‘Target B’.

To this end, the Target choice works in tandem with operations in the ‘Modify’ and ‘Spaceframe’ menus:

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Be aware that Frequency, Class and Breakdown Method should be the same for both targets. Further, the truncation plane of one target must match the truncation plane of the other.

When the Frequency, Class and Breakdown Method are the same for both targets, ‘Target B’ will be superimposed upon ‘Target A’. It is only when you change the envelope extents or the Dual offset of a target that the manifolds separate, thus creating a void for the spaceframe(s) that will connect them.

Trivial Example

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  1. Target A: Primal and Dual
  2. Target B: Primal and Dual. Primal envelope extents increased.
  3. Targets A & B: Primal and Dual
  4. Spaceframe added: ‘Target A Dual Vertex to Target B Dual Vertex’
  5. Spaceframe added: ‘Target B Dual Cell to Target A Primal Vertex’