Functions common to both the Surface Definition and the Surface Interrogation modules.

• Create and Initialize an Instance of a Surface
• Copy an Instance of a Surface
• Free the Space Occupied by a Surface
• Compute Position, Derivatives and Normal of a Surface
  To evaluate and compute the normal and the primary, or all, derivatives of a SISL surface at a given parameter position.
• Compute Position and Left-/Right-hand Derivatives of a Surface
  To evaluate and compute the primary, or all, left-/right-hand derivatives of a SISL surface at a given parameter position.

Subdivide a Surface
To subdivide a SISL surface along a given internal parameter line.

Insert New Knots into the Description of a Surface
To insert a set of new knots into the representation of a SISL surface using the Oslo algorithm.

Pick a Curve in a Surface Along a Constant Parameter Line of the Surface
To make a curve lying in a SISL surface along a given constant parameter line of the surface.

Pick the Curve Lying in a Surface, Described by a Curve in the Parameter Plane of the Surface
To create a 3D approximation to a curve in the parameter plane of a SISL surface.

Pick a Part of a Surface
To pick a rectangular part of a SISL surface and make a new SISL surface of that part.

Turn the Direction of the Surface Normal Vector
To interchange the two parameter directions used in the description of a SISL surface and thereby change the direction of the normal vector to the surface.

Device Dependent Drawing Primitives to Draw a Sequence of Straight Lines
To draw a broken line as a sequence of straight lines described by the array points, in two or three dimensions. Two routines, one to move the graphics cursor and one to draw a line segment, must be interfaced to the host graphics system.

Draw Constant Parameter Lines in a Surface using Piecewise Straight Lines
To draw constant parameter lines in a SISL surface. Uses the previous function for drawing.

Draw Constant Parameter Lines in a Surface Bounded by a Curve
To draw constant parameter lines in a SISL surface. The lines are limited by a closed SISL curve lying in the parameter plane of the surface. All lines are drawn as piecewise straight lines using the function above.