Spline representations

NIKHILKRISHNAN
nikhilkrishnan0101@gmail.com

SPLINE REPRESENTATIONS
 a spline is a flexible strip used to produce a smooth
curve through a designated set of points.
 Several small weights are distributed along the length
of the strip to hold it in position on the drafting table
as the curve is drawn.
 The term spline curve originally referred to a curve
drawn in this manner.
 Mathematically describe such a curve with a piecewise
cubic polynomial function whose first and second
derivatives are continuous across the various curve
sections.

In Computer Graphics, -Splines
Spline curve now refers to any composite curve
formed with polynomial sections satisfying specified
continuity conditions at the boundary of the pieces.
A spline surface can be described with two sets of
orthogonal spline curves.
There are several different kinds of spline
specifications that are used in graphics applications.
Each individual specification simply refers to a
particular type of polynomial with certain specified
boundary conditions.

Splines are used in
1. Graphic applications to design curve and surface
shapes.
2. To digitize drawings for computer storage.
3. To specify Animation paths for the objects for the
camera in a scene.
4. Typical CAD applications for splines include the
design automobile bodies.
5. Aircraft, Spacecraft surfaces & Ship hulls.

Interpolation & Approximation splines
Spline curve by giving a set of coordinate positions,
called control points.
Which indicates the general shape of the curve.
Fitted with piecewise continuous parametric
polynomial functions in one of two ways.
Interpolation
Approximatio n

Interpolation
“Polynomial sections are fitted so that the curve passes
through each control point, Resulting curve is said to
interpolate the set of control points.”
 Interpolation curves are commonly used to digitize
drawings or to specify animation paths.

Approximation
“The polynomials are fitted to thegeneral control-point path
without necessarily passing through any control point, the
resulting curve is said to approximate the set of control
points.”
 Approximation curves are primarily used as design tools to
structure object surfaces
 approximation spline surface created for a design
application. Straight lines connect the control-point
positions above the surface.

Spline Curve
 A spline curve is defined, modified, and manipulated with
operations on the control points.
 By interactively selecting spatial positions for the control
points, a designer can set up an initial curve.
 Designer can then reposition some or all of the control
points to restructure the shape of the curve.
 The curve can be translated, rotated, or scaled with
transformations applied to the control points.
 CAD packages can also insert extra control points to aid a
designer in adjusting the curves shapes.

CONVEX HULL
 The convex polygon boundary that encloses a set of
control points is called the convex hull.
 Convex hulls provide a measure for the deviation of a
curve or surface from the region bounding the control
points.
 Some splines are bounded by the convex hull, thus
ensuring that the polynomials smoothly follow the
control points without erratic oscillations.
 The polygon region inside the convex hull is useful in
some algorithms as a clipping region.

CONTROL GRAPH
 A polyline connecting the sequence of control points
for an approximation spline is usually displayed to
remind a designer of the control-point ordering.
 This set of connected line segments is often referred
to as the control graph of the curve. Other names for
the series of straight-line sections connecting the
control points in the order specified are control
polygon and characteristic polygon.

An approximation splines surface for a CAD
application in automotive design

Spline representations

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