vlax-curve-getDistAtPoint, vlax-curve-getParamAtPoint

Hi guys, I have some question:

Whats the difference between "distance" and "parameter" on vlax-curve-**** functions?

I can't imagine it graphically...

Does "parameter" means the length value of the curve at a given point from it?

For example, if the curve is "unrolled" up to a straight line, and measured.

If so, what does "Distance" mean?

I've been reading several times acad's help file, but I don't/can't understand/imagine the difference.

From help the paramatpoint can give tangent angle for a curve or ellipse.

Distatpoint gives you distance - just opposite of what you stated Grrr, and like BIGAL pointed parameters are numerical derivation of curve from which you can get other data - vector of tangent (vlax-curve-getfirstderiv curve param), or secondderiv which data can be used in calculation position of center and radius of curvature at that parameter of curve belonging to your reference point on curve... Starting parameter may have value different than 0.0 - for distances it's always 0.0, and for POLYLINES it was implemented such convention that for every vertex of polyline, parameter should be every next floating integer number (for first vertex - param=0.0, for second - param=1.0, ... , for last vertex - param=number of vertices - 1 in floating form...)

Thank you for the explanation, Marko!

I was hoping for you to reply (as I've read some of your old posts about vlax-curve-* functions, surely you know alot about them).

I did some experiments with ParamAtPoint on polylines, where the results on the vertices are exactly as you mentioned (still this seems kinda odd for me).

Sorry for my late reply.

I still can't utilize (vlax-curve-getfirstderiv curve param), quoted from help:

Signature
(vlax-curve-getFirstDeriv curve-obj param)

curve-obj
Type: VLA-object
The object to be measured.

param
Type: Integer or Real
A number specifying a parameter on the curve.

Return Values
Type: List or nil
[b]A 3D vector, if successful[/b]; otherwise nil.

When I have this list representing that "3D vector", how can I emake/grdraw the tangent on a given parameter?

Can someone post examples about using First/Second Deriv?

Sorry if I'm going slightly offtopic.

A example

(defun alg-ang (obj pnt)
 (angle '(0. 0. 0.)
    (vlax-curve-getfirstderiv
      obj
      (vlax-curve-getparamatpoint
        obj
        pnt
      )
    )
 )
)

A example

 

(defun alg-ang (obj pnt)
 (angle '(0. 0. 0.)
    (vlax-curve-getfirstderiv
      obj
      (vlax-curve-getparamatpoint
        obj
        pnt
      )
    )
 )
)

Thank you so much, Big Al !