[gambit2.2]What does "geometry not C1 or G1" meant?

[1]. http://www.caddigest.com/subjects/solidworks/select/cadcamnet_proe_vs_solidworks.htm
Curvature continuity
To appreciate what enables CAD software to produce graceful flowing curves, it’s important to understand some concepts of continuous curvature. The curvature of a curve or surface is the inverse of the radius of the curve at each point along its length. An arc, circle, or cylinder has a constant curvature as does a straight line or plane whose curvature is zero. When a circular fillet is tangent to a straight-line segment, the curvature falls abruptly from a constant value to zero.
The human eye can perceive abrupt changes in the curvature of surfaces. A round fillet meeting a plane surface appears to have a ridge at its edge, even though none physically exists. Artfully designed products thus avoid discontinuities in the derivative (rate of change) of the curvature of curves and surfaces except where ridges and sharp edges are used for accent. Entities whose curvature derivative is continuous are said to be C2 (or sometimes G2) continuous. Curves and surfaces that are tangent are said to be C1 (or G1) continuous, while continuous curves or surfaces with sharp edges are said to be C0 (or G0) continuous.
Most CAD systems can produce curves and surfaces that are continuous (C0) or tangent (C1). However, only the best systems can produce surfaces that can be joined with C2 continuity under a wide range of conditions. Pro/Engineer Wildfire maintains C2 continuity between adjacent surfaces under more conditions than SolidWorks 2004.

[2].http://www.cs.stevens.edu/~quynh/courses/cs537-notes/lesson6-CurvesAndSurfaces.ppt#257,2,Curves and Surfaces

Joining Curve Segments Together
G0 geometric continuity: Two curve segments join together
G1 geometric continuity: The direction of the two segments’ tangent vectors are equal at the join point
C1 (parametric) continuity: Tangent vectors of the two segments are equal in magnitude and direction
(C1 Þ G1 unless tangent vector = [0, 0, 0])
Cn (parametric) continuity: Direction and magnitude through the nth derivative are equal at the join point



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