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Program: Visualization Toolkit
Module: vtkProjectedTerrainPath.h
Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
All rights reserved.
See Copyright.txt or for details.
This software is distributed WITHOUT ANY WARRANTY; without even
PURPOSE. See the above copyright notice for more information.
// .NAME vtkProjectedTerrainPath - project a polyline onto a terrain
// .SECTION Description
// vtkProjectedTerrainPath projects an input polyline onto a terrain. (The
// terrain is defined by a 2D height image and is the second input to the
// filter.) The polyline projection is controlled via several modes as
// follows. 1) Simple mode projects the polyline points onto the terrain,
// taking into account the height offset instance variable. 2) Non-occluded
// mode insures that no parts of the polyline are occluded by the terrain
// (e.g. a line passes through a mountain). This may require recursive
// subdivision of the polyline. 3) Hug mode insures that the polyine points
// remain within a constant distance from the surface. This may also require
// recursive subdivision of the polyline. Note that both non-occluded mode
// and hug mode also take into account the height offset, so it is possible
// to create paths that hug terrain a certain distance above it. To use this
// filter, define two inputs: 1) a polyline, and 2) an image whose scalar
// values represent a height field. Then specify the mode, and the height
// offset to use.
// An description of the algorithm is as follows. The filter begins by
// projecting the polyline points to the image (offset by the specified
// height offset). If the mode is non-occluded or hug, then the maximum
// error along each line segment is computed and placed into a priority
// queue. Each line segment is then split at the point of maximum error, and
// the two new line segments are evaluated for maximum error. This process
// continues until the line is not occluded by the terrain (non-occluded
// mode) or satisfies the error on variation from the surface (hug
// mode). (Note this process is repeated for each polyline in the
// input. Also, the maximum error is computed in two parts: a maximum
// positive error and maximum negative error. If the polyline is above the
// terrain--i.e., the height offset is positive--in non-occluded or hug mode
// all negative errors are eliminated. If the polyline is below the
// terrain--i.e., the height offset is negative--in non-occluded or hug mode
// all positive errors are eliminated.)
// .SECTION Caveats
// This algorithm requires the entire input image to be in memory, hence it
// may not work for extremely large images.
// The input height image is assumed to be positioned in the x-y plane so the
// scalar value is the z-coordinate, height value.
// A priority queue is used so that the 1) the total number of line segments
// can be controlled, and 2) the algorithm can terminate when the errors in
// the queue are less than the specified error tolerance.
// .SECTION See Also
// vtkGreedyTerrainDecimation
#ifndef __vtkProjectedTerrainPath_h
#define __vtkProjectedTerrainPath_h
#include "vtkPolyDataAlgorithm.h"
class vtkPriorityQueue;
class vtkImageData;
class vtkEdgeList;
class vtkPoints;
class VTK_HYBRID_EXPORT vtkProjectedTerrainPath : public vtkPolyDataAlgorithm
// Description:
// Standard methids for printing and determining type information.
void PrintSelf(ostream& os, vtkIndent indent);
// Description:
// Instantiate the class.
static vtkProjectedTerrainPath* New();
// Description:
// Specify the second input (the terrain) onto which the polyline(s) should
// be projected.
void SetSource(vtkImageData *source);
vtkImageData *GetSource();
// Description:
// Determine how to control the projection process. Simple projection
// just projects the original polyline points. Non-occluded projection
// insures that the polyline does not intersect the terrain surface.
// Hug projection is similar to non-occulded projection except that
// produces a path that is nearly parallel to the terrain (within the
// user specified height tolerance).
void SetProjectionModeToSimple()
void SetProjectionModeToNonOccluded()
void SetProjectionModeToHug()
// Description:
// This is the height above (or below) the terrain that the projected
// path should be. Positive values indicate distances above the terrain;
// negative values indicate distances below the terrain.
// Description:
// This is the allowable variation in the altitude of the path
// with respect to the variation in the terrain. It only comes
// into play if the hug projection mode is enabled.
// Description:
// This instance variable can be used to limit the total number of line
// segments created during subdivision. Note that the number of input line
// segments will be the minimum number that cab be output.
virtual int RequestData(vtkInformation *, vtkInformationVector **,
vtkInformationVector *);
virtual int FillInputPortInformation(int port, vtkInformation *info);
// Supporting methods
void GetImageIndex(double x[3], double loc[2], int ij[2]);
double GetHeight(double loc[2], int ij[2]);
void ComputeError(vtkIdType edgeId);
void RemoveOcclusions();
void HugTerrain();
void SplitEdge(vtkIdType eId, double t);
//ivars that the API addresses
int ProjectionMode;
double HeightOffset;
double HeightTolerance;
vtkIdType MaximumNumberOfLines;
//Bookeeping arrays
int Dimensions[3];
int Extent[6];
double Origin[3];
double Spacing[3];
vtkDataArray *Heights;
vtkPoints *Points;
vtkIdType NumLines;
//Errors above/below terrain. In both instances, negative values are
//inserted because the priority queue puts smallest values on top.
vtkPriorityQueue *PositiveLineError; //errors above terrain
vtkPriorityQueue *NegativeLineError; //errors below terrain
//This is a PIMPL'd vector representing edges
vtkEdgeList *EdgeList;
vtkProjectedTerrainPath(const vtkProjectedTerrainPath&); // Not implemented.
void operator=(const vtkProjectedTerrainPath&); // Not implemented.
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