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`SKEL`

files represent collections of points and polylines, with
shared vertices.
The conventional suffix for `SKEL`

files is `.skel`.

Syntax:

[C][4][n]SKEL [NDim] # Vertex dimension, present only if nSKELNVerticesNPolylinesx[0]y[0]z[0] # Vertices # if 4SKEL, each vertex has 4 components # if nSKEL, each vertex has NDim components # if C[4][n]SKEL vertex coordinates are # followed by an RGBA color specification ...x[NVertices-1]y[NVertices-1]z[NVertices-1] # Polylines #Nv= # vertices on this polyline (1 = point) #v[0] ...v[Nv-1]: vertex indices # in range 0..NVertices-1Nvv[0]v[1] ...v[Nv-1] [colorspec] ... #colorspeccontinues pastv[Nv-1] # to end-of-line; may be nothing, or 3 or 4 numbers. # nothing: default color # 3 or 4 floats: RGB[A] values 0..1

The syntax resembles that of `OFF`

files, with a table of vertices
followed by a sequence of polyline descriptions, each referring to vertices
by index in the table. Each polyline has an optional color.

For `nSKEL`

objects, each vertex has `NDim` components.
For `4nSKEL`

objects, each vertex has `NDim+1` components;
the final component is the homogeneous divisor.

A `[4][n]SKEL BINARY` format is accepted; See Binary format.
It resembles the ASCII format in almost the way you'd expect,
with 32-bit integers for all counters and vertex indices and 32-bit
floats for vertex positions.

Exception: each polyline's vertex indices are followed by an integer indicating how many color components accompany it. Polyline color components must be floats, not integer values. Thus a colorless polyline with 3 vertices might be represented as

int int int int int 3 17 5 9 0

while the same polyline colored red might be

int int int int int float float float float 3 17 5 9 4 1.0 0.0 0.0 1.0