tangent of spline point

Helper

On 05/05/2013 at 11:57, xxxxxxxx wrote:

If I wanted to move the points of a spline.
This is the way I'd do it:

#include "lib_splinehelp.h"  
  
  
  BaseDocument *doc = GetActiveDocument();  
  BaseObject *spline = doc->SearchObject("Spline");  
  PointObject *sp = ToPoint(spline);  
  
  AutoAlloc<SplineHelp> sh;  
  if(!sh) return FALSE;  
  sh->InitSpline(sp);  
  if(!sh->Exists()) return FALSE;  
  
  Vector *spPnts = sp->GetPointW();           //Get all the points in the spline  
  
  Real offsetX = 100.0;  
  Real offsetY = 100.0;                       //Some offset values that can be bound to GUI gizmos  
  Real offsetZ = 100.0;  
  
  LONG pntCnt = sh->GetPointCount();  
  for(LONG i=0; i<pntCnt; i++)  
  {  
      spPnts[i].x += offsetX;  
      spPnts[i].y += offsetY;                 //Move all the points in the spline by this offset amount  
      spPnts[i].z += offsetZ;  
  }  
  
  sp->Message(MSG_UPDATE);                    //Update the changes made to the spline

-ScottA

Helper

On 06/05/2013 at 00:15, xxxxxxxx wrote:

yes, i know how to move points, but how do i get the direction when there is no tangent and when i need to take care that the points need to move all relatively to the right or left side of the spline.. thats the main problem i have here

Helper

On 06/05/2013 at 03:07, xxxxxxxx wrote:

You can get the bisecting vector of a point by calculating the arithmetic middle of the adjacent points.

Helper

On 06/05/2013 at 04:26, xxxxxxxx wrote:

i guess you mean something like

tRot = Vector((getAngle(points[i-1],points[i]).x+getAngle(points[i+1],points[i]).x)/2,0,0);
  
Matrix richtung = HPBToMatrix(tRot, ROTATIONORDER_DEFAULT);
tPos += Vector(0,0,_ipOffset)*richtung;

this still makes some objects move to the one direction end others to the opposite direction...

Helper

On 06/05/2013 at 14:13, xxxxxxxx wrote:

double post, sorry.

Helper

On 06/05/2013 at 14:15, xxxxxxxx wrote:

Not exactly. But I expressed myself not 100% correct. You can get a point that lies on the bisecting
line this way:

p1 = points[i]
p2 = (points[i - 1] + points[i + 1]) * (1 / 2.0)   // I think division is not supported by the vector class
bv = (p2 - p1).GetNormalized()

Then again you can cross it with one of the adjacent lines and cross it
again and you have the tangent:

n = bv.Cross(points[i] - points[i - 1])
tangent = bv.Cross(n)

Best,
Niklas

Helper

On 06/05/2013 at 21:32, xxxxxxxx wrote:

thank you niklas. i'll try if this helps me solve my problem and report back...

Helper

On 07/05/2013 at 01:44, xxxxxxxx wrote:

hm, this still produces the wrong direction for some points. i have no idea how to get this working...

Helper

On 07/05/2013 at 03:18, xxxxxxxx wrote:

Hi ello,

here, some example code quickly plucked together.

import c4d
  
class Tag(c4d.plugins.TagData) :
  
    SIZE_SPHERE = c4d.Vector(10)
    COLOR_SPHERE = c4d.Vector(1, 0.66, 0.02)
  
    LENGTH_TANGENT = 20
    COLOR_TANGENT = c4d.Vector(0.1, 0.95, 0.5)
  
    def Draw(self, tag, op, bd, bh) :
  
        if not isinstance(op, c4d.SplineObject) :
            return True
  
        bd.SetMatrix_Matrix(op, op.GetMg())
        segments = [op.GetSegment(i) for i in xrange(op.GetSegmentCount())]
        if not segments:
            segments = [{'cnt': op.GetPointCount(), 'closed': op.IsClosed()}]
  
        pi = 0
        for segment in segments:
            cnt = segment['cnt']
            closed = segment['closed']
  
            start = pi
            end = pi + cnt
            i_start = start
            i_end = end
            if not closed:
                i_start += 1
                i_end -= 1
  
                bd.DrawSphere(op.GetPoint(pi), self.SIZE_SPHERE, self.COLOR_SPHERE, 0)
                bd.DrawSphere(op.GetPoint(pi + cnt - 1), self.SIZE_SPHERE, self.COLOR_SPHERE, 0)
  
            bd.SetPen(self.COLOR_TANGENT)
            if start < end:
                for i in xrange(i_start, i_end, 1) :
                    left = i - 1
                    right = i + 1
  
                    if left < start:
                        left = end - 1
                    if right >= end:
                        right = start
  
                    print left, i, right
  
                    pleft = op.GetPoint(left)
                    pright = op.GetPoint(right)
                    point = op.GetPoint(i)
  
                    mid = (pleft + pright) * 0.5
                    bv = point - mid
                    n = bv.Cross(point - pleft)
                    tangent = n.Cross(bv).GetNormalized() * self.LENGTH_TANGENT
  
                    pmin = point - tangent
                    pmax = point + tangent
                    bd.DrawLine(pmin, pmax, 0)
  
            pi += cnt
  
        print "-------------------"
  
        return True
  
if __name__ == "__main__":
    c4d.plugins.RegisterTagPlugin(100003, "Spline Tangents", c4d.TAG_VISIBLE, Tag, "Tsplinetangents", None)

Best,
-Niklas

http://www.file-upload.net/download-7562607/spline-tangents.zip.html

Helper

On 07/05/2013 at 03:20, xxxxxxxx wrote:

Originally posted by xxxxxxxx

this still makes some objects move to the one direction end others to the opposite direction...

Uhm, I just see: The result in the image is correct. What else did you expect?
The only thing left would be to rotate them about 90° to get the actual tangent (see my example code).

Helper

On 07/05/2013 at 04:05, xxxxxxxx wrote:

thank you very much, but when i rotate the direction the problem still remains. it just doesnt move left/right but back and forward.. still some point to the opposite..