package com.github.mikephil.charting.data.filter;
import com.github.mikephil.charting.data.Entry;
import java.util.ArrayList;
import java.util.List;
/**
* Implemented according to Wiki-Pseudocode {@link}
* http://en.wikipedia.org/wiki/Ramer�Douglas�Peucker_algorithm
*
* @author Philipp Baldauf & Phliipp Jahoda
*/
public class Approximator {
/** the type of filtering algorithm to use */
private ApproximatorType mType = ApproximatorType.DOUGLAS_PEUCKER;
/** the tolerance to be filtered with */
private double mTolerance = 0;
private float mScaleRatio = 1f;
private float mDeltaRatio = 1f;
/**
* array that contains "true" on all indices that will be kept after
* filtering
*/
private boolean[] keep;
/** enums for the different types of filtering algorithms */
public enum ApproximatorType {
NONE, DOUGLAS_PEUCKER
}
/**
* Initializes the approximator with type NONE
*/
public Approximator() {
this.mType = ApproximatorType.NONE;
}
/**
* Initializes the approximator with the given type and tolerance. If
* toleranec <= 0, no filtering will be done.
*
* @param type
*/
public Approximator(ApproximatorType type, double tolerance) {
setup(type, tolerance);
}
/**
* sets type and tolerance, if tolerance <= 0, no filtering will be done
*
* @param type
* @param tolerance
*/
public void setup(ApproximatorType type, double tolerance) {
mType = type;
mTolerance = tolerance;
}
/**
* sets the tolerance for the Approximator. When using the
* Douglas-Peucker-Algorithm, the tolerance is an angle in degrees, that
* will trigger the filtering.
*/
public void setTolerance(double tolerance) {
mTolerance = tolerance;
}
/**
* Sets the filtering algorithm that should be used.
*
* @param type
*/
public void setType(ApproximatorType type) {
this.mType = type;
}
/**
* Sets the ratios for x- and y-axis, as well as the ratio of the scale
* levels
*
* @param deltaRatio
* @param scaleRatio
*/
public void setRatios(float deltaRatio, float scaleRatio) {
mDeltaRatio = deltaRatio;
mScaleRatio = scaleRatio;
}
/**
* Filters according to type. Uses the pre set set tolerance
*
* @param points the points to filter
* @return
*/
public List<Entry> filter(List<Entry> points) {
return filter(points, mTolerance);
}
/**
* Filters according to type.
*
* @param points the points to filter
* @param tolerance the angle in degrees that will trigger the filtering
* @return
*/
public List<Entry> filter(List<Entry> points, double tolerance) {
if (tolerance <= 0)
return points;
keep = new boolean[points.size()];
switch (mType) {
case DOUGLAS_PEUCKER:
return reduceWithDouglasPeuker(points, tolerance);
case NONE:
return points;
default:
return points;
}
}
/**
* uses the douglas peuker algorithm to reduce the given List of
* entries
*
* @param entries
* @param epsilon
* @return
*/
private List<Entry> reduceWithDouglasPeuker(List<Entry> entries, double epsilon) {
// if a shape has 2 or less points it cannot be reduced
if (epsilon <= 0 || entries.size() < 3) {
return entries;
}
// first and last always stay
keep[0] = true;
keep[entries.size() - 1] = true;
// first and last entry are entry point to recursion
algorithmDouglasPeucker(entries, epsilon, 0, entries.size() - 1);
// create a new array with series, only take the kept ones
List<Entry> reducedEntries = new ArrayList<Entry>();
for (int i = 0; i < entries.size(); i++) {
if (keep[i]) {
Entry curEntry = entries.get(i);
reducedEntries.add(new Entry(curEntry.getVal(), curEntry.getXIndex()));
}
}
return reducedEntries;
}
/**
* apply the Douglas-Peucker-Reduction to an List of Entry with a given
* epsilon (tolerance)
*
* @param entries
* @param epsilon as y-value
* @param start
* @param end
*/
private void algorithmDouglasPeucker(List<Entry> entries, double epsilon, int start,
int end) {
if (end <= start + 1) {
// recursion finished
return;
}
// find the greatest distance between start and endpoint
int maxDistIndex = 0;
double distMax = 0;
Entry firstEntry = entries.get(start);
Entry lastEntry = entries.get(end);
for (int i = start + 1; i < end; i++) {
double dist = calcAngleBetweenLines(firstEntry, lastEntry, firstEntry, entries.get(i));
// keep the point with the greatest distance
if (dist > distMax) {
distMax = dist;
maxDistIndex = i;
}
}
// Log.i("maxangle", "" + distMax);
if (distMax > epsilon) {
// keep max dist point
keep[maxDistIndex] = true;
// recursive call
algorithmDouglasPeucker(entries, epsilon, start, maxDistIndex);
algorithmDouglasPeucker(entries, epsilon, maxDistIndex, end);
} // else don't keep the point...
}
/**
* calculate the distance between a line between two entries and an entry
* (point)
*
* @param startEntry line startpoint
* @param endEntry line endpoint
* @param entryPoint the point to which the distance is measured from the
* line
* @return
*/
public double calcPointToLineDistance(Entry startEntry, Entry endEntry, Entry entryPoint) {
float xDiffEndStart = (float) endEntry.getXIndex() - (float) startEntry.getXIndex();
float xDiffEntryStart = (float) entryPoint.getXIndex() - (float) startEntry.getXIndex();
double normalLength = Math.sqrt((xDiffEndStart)
* (xDiffEndStart)
+ (endEntry.getVal() - startEntry.getVal())
* (endEntry.getVal() - startEntry.getVal()));
return Math.abs((xDiffEntryStart)
* (endEntry.getVal() - startEntry.getVal())
- (entryPoint.getVal() - startEntry.getVal())
* (xDiffEndStart))
/ normalLength;
}
/**
* Calculates the angle between two given lines. The provided Entry objects
* mark the starting and end points of the lines.
*
* @param start1
* @param end1
* @param start2
* @param end2
* @return
*/
public double calcAngleBetweenLines(Entry start1, Entry end1, Entry start2, Entry end2) {
double angle1 = calcAngleWithRatios(start1, end1);
double angle2 = calcAngleWithRatios(start2, end2);
return Math.abs(angle1 - angle2);
}
/**
* calculates the angle between two Entries (points) in the chart taking
* ratios into consideration
*
* @param p1
* @param p2
* @return
*/
public double calcAngleWithRatios(Entry p1, Entry p2) {
float dx = p2.getXIndex() * mDeltaRatio - p1.getXIndex() * mDeltaRatio;
float dy = p2.getVal() * mScaleRatio - p1.getVal() * mScaleRatio;
double angle = Math.atan2(dy, dx) * 180.0 / Math.PI;
return angle;
}
/**
* calculates the angle between two Entries (points) in the chart
*
* @param p1
* @param p2
* @return
*/
public double calcAngle(Entry p1, Entry p2) {
float dx = p2.getXIndex() - p1.getXIndex();
float dy = p2.getVal() - p1.getVal();
double angle = Math.atan2(dy, dx) * 180.0 / Math.PI;
return angle;
}
}