"Normal" in GDL

[Anonymous]

In the Archicad Help dbx, under the TUBE definitition, there is a note that say, "Note: The path comprises two points more than the number of generated sections. The first and the last points determine the position in space of the first and the last surfaces belonging to the TUBE. These points only play a role in determining the normal of the surfaces, they are not actual nodes of the path. The orientation of the surfaces is the same as that of the surfaces that would be generated at the nodes nearest to the two endpoints, if the TUBE were continued in the directions indicated by these.)".

What is the "normal" that it's referring to? This is the only part of the TUBE definition that I don't understand.

Thanks in advance.

[James Murray]

The phantom points determine the miters at the beginning and end of the tube. The ends will be angled to meet imaginary segments between the real ends and the phantom points.

Recent specific example here.

HTH,

[Anonymous]

So...Let's say I create a 3d object based on a rectangle. The final object in 'plan' view looks like the Letter 'U' (3 sides total). I make the object by starting on the left hand side of the 'U'. That means I draw in a 270 degree direction for the first line of the path, a 0 degree direction for the second leg of the path, and a 90 degree direction for the last leg of the path. That means in GDL there will be 5 coordinates, 3 of which are the path, and the first and last are the "normal" that this is talking about. In this example, what would the "normal" be? Is it a point in a plane that's 90 degree's in the z direction (in plan view) coming toward me or what?

Thanks for any help.

[Ignacio Azpiazu]

'Normal' means perpendicular, what they are saying is that the first and last points are not part of the tube itself and are needed for determining the normal to (the perpendicular to the plane that contains) the end faces, which is like saying 'used for determining the plane'.

The orientation of the start and end faces is that of a mitered/mitred joint with the first and last 'invisible' segments of the tube. (So that if you want the start face to be perpendicular to the axis of the first segment, the first 'reference' point should be along the axis of the first true tube segment, as if you were extending it --the 'mitered' joint of the invisible start tube and your first true tube giving you the butt joint/perpendicular plane.)

[Anonymous]

Does this help?

Think of the tube as a set of edges. The cross section at each vertex is created on the mitre angle between the two edges.


For example, if you want a 45 degree end on the tube, you would create a 90 degree angle between the last two edges.

tube 4,4,51, !m, n, mask
0,0,0, !profile points (all sharp edges) …
w,0,0,
w,h,0,
0,h,0, !end of profile points
-1,0,0,0, !path points (a ‘lead in’ edge starts at - 1,0,0; angles all zero) …
0,0,0,0,
a,0,0,0,
a,1,0,0 !end of path points (the ‘tail out’ edge ends at a,1,0 - that is at 90 degrees to the previous edge, so forms a 45 degree angle)

[Laszlo Nagy]

I have included the illustration found at the TUBE command in the Help file. Watch the little index numbers along the path (thick multi-segment line in space): at the beginning 1, 2 then at the end of the path: m-1, m. Point 1 and point m do not create an actual TUBE segment; they are only there for the definition of the beginning and ending NORMALs of the beginning and ending sections of the TUBE.

[Anonymous]

Thank you, all of you, for your help! I think I got it now (we'll find out the more I experiment with it).