Hello,
If you're referring to my post, in wich one could find a polygon oriented
algorithm, here's the answer :
A polyline can be handled just like an unclosed polygon. Take a look at the
implementation, you'll see it's not a problem. The algorithm computes the
signed area of the polygon constitued by the polylines segments, and adds
the last, closing one ... Depending on the general shape of your polylines,
it might be wiser (and enough) to study the rotation of 3 consecutive nodes
(2 segments and a virtual closing one). That would define a triangle, made
of the 3 first nodes of your polyline, and should be enough to check CCW.
For information, the mathematical background of this is about direct or
inverse orientation of consecutive node in a given axis system (remember
the corkscrew turning right or left or fiddling with your fingers (3
fingers painted with x,y,z) in your math class?). This kind of check is
needed if you display a triangle (polygon) in a display viewport, for it
defines where the surface normal is pointing to, and thus on wich side of
the triangle it has to be drawn (in the computer world, a triangle has two
faces, and only one has to be drawn: the one facing the user). Please refer
to your favorite geometry and trigonometry class book for more accurate
details :), and avoid twisting your elbow too much ...
Eric Maranne
EMI Informatiques
web : www.cycweb.com/equipage
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GIS - VRML Integration
> -----Message d'origine-----
> De: MAPPER MAN [SMTP:[EMAIL PROTECTED]]
> Date: jeudi 24 fevrier 2000 22:24
> A: [EMAIL PROTECTED]
> Objet: MI re: Line Direction
>
> who was the owner of the question ? i found a algorithm for this question
> but it is working for poligon..
>
> i wanna ask what is the meaning of a polyline object clockwise direction
?
> it can have a general south north east northeast ... direction but to
have
> a clockwise or counterclockwise direction it must be a closed polyline
???
>
> Maper Man
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