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EvaluateAtPoint Method (ISurface)

Evaluates a surface at the specified XYZ point.

.NET Syntax

Visual Basic (Declaration) 
Function EvaluateAtPoint( _
   ByVal PositionX As System.Double, _
   ByVal PositionY As System.Double, _
   ByVal PositionZ As System.Double _
) As System.Object
Visual Basic (Usage) 
Dim instance As ISurface
Dim PositionX As System.Double
Dim PositionY As System.Double
Dim PositionZ As System.Double
Dim value As System.Object
value = instance.EvaluateAtPoint(PositionX, PositionY, PositionZ)
System.object EvaluateAtPoint( 
   System.double PositionX,
   System.double PositionY,
   System.double PositionZ
System.Object^ EvaluateAtPoint( 
&   System.double PositionX,
&   System.double PositionY,
&   System.double PositionZ



X position


Y position


Z position

Return Value

Array of doubles (see Remarks)



This method calculates the normal, the principal directions, and the principal curvatures, of the surface at the specified point.

Use IFace2::FaceInSurfaceSense to check the directions of the face normal and surface normal. IFace2::FaceInSurfaceSense returns true when the face normal and surface normal point in opposite directions, and false when they point in the same direction.

The return value is the following array of eleven doubles:

[surfNorm[i, j, k], principalDir1[i, j, k], principalDir2[I, j, k], principalCurvature1, principalCurvature2 ]


surfNorm[i, j, k] = normalized vector describing the surface normal

principalDir1[i, j, k] = normalized vector describing the first principal direction

principalDir2[i, j, k] = normalized vector describing the second principal direction

principalCurvature1 = first principal curvature

principalCurvature2 = second principal curvature

Principal Curvature 1 is the minimum normal curvature at the point (largest radius). Principal Curvature 2 is the maximum normal curvature at the point.

The tangent direction producing Principal Curvature 1 is called the first principal direction, and the tangent direction producing Principal Curvature 1 is called the second principal direction.

It is a property of differentiable surfaces that principalDir1 and principalDir2 are orthogonal.

A positive curvature by convention implies a centre of curvature on the side pointed away from by the surface normal (convex).

See "Faux and Pratt Computational Geometry for Design and Manufacture" for more information.


See Also

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