nentselp

nentsel

N Functions

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nentselp

Provides similar functionality to that of the nentsel function without the need for user input

(nentselp [msg] [pt]) 

Arguments

msg

A string to be displayed as a prompt. If the msg argument is omitted, the Select object prompt is issued.

pt

A selection point. This allows object selection without user input.

Return Values

The nentselp function returns a 4×4 transformation matrix, defined as follows:

The first three columns of the matrix specify scaling and rotation. The fourth column is a translation vector.

The functions that use a matrix of this type treat a point as a column vector of dimension 4. The point is expressed in homogeneous coordinates, where the fourth element of the point vector is a scale factor that is normally set to 1.0. The final row of the matrix, the vector [M₃₀M₃₁M₃₂M₃₃], has the nominal value of [0 0 0 1]; it is currently ignored by the functions that use this matrix format. In this convention, applying a transformation to a point is a matrix multiplication that appears as follows:

This multiplication gives us the individual coordinates of the point as follows:

As these equations show, the scale factor and the last row of the matrix have no effect and are ignored.