org.tinfour.interpolation

Class TriangularFacetInterpolator

java.lang.Object

org.tinfour.interpolation.TriangularFacetInterpolator

All Implemented Interfaces:

IProcessUsingTin, IInterpolatorOverTin

public class TriangularFacetInterpolator
extends Object
implements IInterpolatorOverTin

Provides interpolation based on treating the surface as a collection of planar triangular facets.

Constructor Summary

Constructors

Constructor and Description
TriangularFacetInterpolator(IIncrementalTin tin) Construct an interpolator that operates on the specified TIN.

Method Summary

Modifier and Type	Method and Description
String	getMethod() Gets a string describing the interpolation method that can be used for labeling graphs and printouts.
double[]	getSurfaceNormal() Gets the unit normal to the surface at the position of the most recent interpolation.
double	interpolate(double x, double y, IVertexValuator valuator) Perform linear interpolation treating the triangle that contains the query point as a flat plane.
double	interpolateWithExteriorSupport(double x, double y, IVertexValuator valuator) Performs an interpolation with special handling to provide values for regions to the exterior of the Delaunay Triangulation.
boolean	isSurfaceNormalSupported() Indicates whether the interpolation class supports the computation of surface normals through the getUnitNormal() method.
void	resetForChangeToTin() Used by an application to reset the state data within the interpolator when the content of the TIN may have changed.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TriangularFacetInterpolator

public TriangularFacetInterpolator(IIncrementalTin tin)

Construct an interpolator that operates on the specified TIN. Because the interpolator will access the TIN on a read-only basis, it is possible to construct multiple instances of this class and allow them to operate in parallel threads.

Important Synchronization Issue

To improve performance, the classes in this package frequently maintain state-data about the TIN that can be reused for query to query. They also avoid run-time overhead by not implementing any kind of Java synchronization or or even the concurrent-modification testing provided by the Java collection classes. If an application modifies the TIN, instances of this class will not be aware of the change. In such cases, interpolation methods may fail by either throwing an exception or, worse, returning an incorrect value. The onus is on the calling application to manage the use of this class and to ensure that no modifications are made to the TIN between interpolation operations. If the TIN is modified, the internal state data for this class must be reset using a call to resetForChangeToTIN().

Parameters:

tin - a valid instance of an incremental TIN.

Method Detail

resetForChangeToTin

public void resetForChangeToTin()

Used by an application to reset the state data within the interpolator when the content of the TIN may have changed. Reseting the state data unnecessarily may result in a minor performance reduction when processing a large number of interpolations, but is otherwise harmless.

Specified by:

resetForChangeToTin in interface IProcessUsingTin

interpolate

public double interpolate(double x,
                          double y,
                          IVertexValuator valuator)

Perform linear interpolation treating the triangle that contains the query point as a flat plane. This interpolation develops a continuous surface, but does not provide first-derivative continuity at the edges of triangles.

This interpolation is not defined beyond the convex hull of the TIN and this method will produce a Double.NaN if the specified coordinates are exterior to the TIN.

Specified by:

interpolate in interface IInterpolatorOverTin

Parameters:

x - the x coordinate for the interpolation point

y - the y coordinate for the interpolation point

valuator - a valid valuator for interpreting the z value of each vertex or a null value to use the default.

Returns:

if the interpolation is successful, a valid floating point value; otherwise, a NaN.

isSurfaceNormalSupported

public boolean isSurfaceNormalSupported()

Description copied from interface: IInterpolatorOverTin

Indicates whether the interpolation class supports the computation of surface normals through the getUnitNormal() method.

Specified by:

isSurfaceNormalSupported in interface IInterpolatorOverTin

Returns:

true if the class implements the ability to compute surface normals; otherwise, false.

getSurfaceNormal

public double[] getSurfaceNormal()

Gets the unit normal to the surface at the position of the most recent interpolation. The unit normal is computed based on the partial derivatives of the surface polynomial evaluated at the coordinates of the query point. Note that this method assumes that the vertical and horizontal coordinates of the input sample points are isotropic.

Specified by:

getSurfaceNormal in interface IInterpolatorOverTin

Returns:

if defined, a valid array of dimension 3 giving the x, y, and z components of the normal, respectively; otherwise, a zero-sized array.

getMethod

public String getMethod()

Description copied from interface: IInterpolatorOverTin

Gets a string describing the interpolation method that can be used for labeling graphs and printouts. Because this string may be used as a column header in a table, its length should be kept short.

Specified by:

getMethod in interface IInterpolatorOverTin

Returns:

A valid string

interpolateWithExteriorSupport

public double interpolateWithExteriorSupport(double x,
                                             double y,
                                             IVertexValuator valuator)

Performs an interpolation with special handling to provide values for regions to the exterior of the Delaunay Triangulation. If the query point (x,y) lies inside the triangulation, the interpolation will be identical to the results from the interpolate() method. If the query point (x,y) lies to the exterior, it will be projected down to the nearest edge and a value will be interpolated between the values of the edge-defining vertices (v0, v1).

When the query point is outside the TIN, the normal vector is computed based on the behavior of the plane generated by the z values in the region adjacent to the perimeter edge.

This method does not perform an extrapolation. Instead, the computed value is assigned the value of the nearest point on the convex hull of the TIN.

Note that this method can still return a NaN value if the TIN is not populated with at least one non-trivial triangle.

Parameters:

x - the planar x coordinate of the interpolation point

y - the planar y coordinate of the interpolation point

valuator - a valid valuator for interpreting the z value of each vertex or a null value to use the default.

Returns:

if successful, a valid floating point value; otherwise, a null.