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[Bugfix] ThrustCurve motor interpolation fixed.

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This commit is contained in:
Daniel_M_Williams 2016-06-25 11:11:28 -04:00
parent 7b2e195392
commit 56463b02fc
2 changed files with 46 additions and 44 deletions
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82
core/src/net/sf/openrocket/motor/ThrustCurveMotor.java
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@ -215,44 +215,51 @@ public class ThrustCurveMotor implements Motor, Comparable<ThrustCurveMotor>, Se
* @return a pseudo index to this motor's data.
*/
protected double getPseudoIndex( final double motorTime ){
final double SNAP_DISTANCE = 0.001;
if( time.length == 0 ){
if(( time.length == 0 )||( 0 > motorTime )){
return Double.NaN;
}
if( 0 > motorTime ){
return 0.0;
}
final int lowerIndex = getIndex( motorTime);
final double fraction = getIndexFraction( motorTime, lowerIndex );
return ((double)lowerIndex)+fraction;
}
private int getIndex( final double motorTime ){
int lowerBoundIndex=0;
int upperBoundIndex=0;
while( ( upperBoundIndex < time.length ) && ( motorTime >= time[upperBoundIndex] )){
lowerBoundIndex = upperBoundIndex;
++upperBoundIndex;
}
lowerBoundIndex = upperBoundIndex-1;
return lowerBoundIndex;
}
private double getIndexFraction( final double motorTime, final int index ){
final double SNAP_DISTANCE = 0.0001;
final int lowerBoundIndex= index;
final int upperBoundIndex= index+1;
// we are already at the end of the time array.
if( upperBoundIndex == time.length ){
return lowerBoundIndex; // == time.length-1;
return 0.;
}
if ( SNAP_DISTANCE > Math.abs( motorTime - time[lowerBoundIndex])){
return lowerBoundIndex;
}
final double lowerBoundTime = time[lowerBoundIndex];
final double upperBoundTime = time[upperBoundIndex];
final double timeFraction = motorTime - lowerBoundTime;
final double indexFraction = ( timeFraction ) / ( upperBoundTime - lowerBoundTime );
double lowerBoundTime = time[lowerBoundIndex];
double upperBoundTime = time[upperBoundIndex];
double timeFraction = motorTime - lowerBoundTime;
double indexFraction = ( timeFraction ) / ( upperBoundTime - lowerBoundTime );
if( indexFraction < SNAP_DISTANCE ){
// round down to last index
return lowerBoundIndex;
}else if( indexFraction > (1-SNAP_DISTANCE)){
if( SNAP_DISTANCE > indexFraction ){
// round down to previous index
return 0.;
}else if( (1-SNAP_DISTANCE)< indexFraction ){
// round up to next index
return ++lowerBoundIndex;
return 1.;
}else{
// general case
return lowerBoundIndex + indexFraction;
return indexFraction;
}
}
@ -304,7 +311,9 @@ public class ThrustCurveMotor implements Motor, Comparable<ThrustCurveMotor>, Se
@Override
public double getThrust( final double motorTime ){
double pseudoIndex = getPseudoIndex( motorTime );
return ThrustCurveMotor.interpolateAtIndex( thrust, pseudoIndex);
final double thrustAtTime= ThrustCurveMotor.interpolateAtIndex( thrust, pseudoIndex);
return thrustAtTime;
}
@Override
@ -369,18 +378,6 @@ public class ThrustCurveMotor implements Motor, Comparable<ThrustCurveMotor>, Se
public double getUnitRotationalInertia() {
return this.unitRotationalInertia;
}
public double getIxx( final double searchTime) {
final double pseudoIndex = getPseudoIndex( searchTime);
//return this.unitLongitudinalInertia * this.getMassAtIndex( index);
return this.unitLongitudinalInertia * interpolateCenterOfMassAtIndex( pseudoIndex).weight;
}
public double getIyy( final double searchTime) {
final double pseudoIndex = getPseudoIndex( searchTime);
//return this.unitRotationalInertia * this.getMassAtIndex( index);
return this.unitRotationalInertia * interpolateCenterOfMassAtIndex( pseudoIndex).weight;
}
@Override
public String getDesignation() {
@ -443,12 +440,13 @@ public class ThrustCurveMotor implements Motor, Comparable<ThrustCurveMotor>, Se
private static double interpolateAtIndex( final double[] values, final double pseudoIndex ){
final double SNAP_TOLERANCE = 0.0001;
// assumes that pseudoIndex > 1
final double upperFrac = pseudoIndex%1;
final double lowerFrac = 1-upperFrac;
final int lowerIndex = (int)pseudoIndex;
final int upperIndex= lowerIndex+1;
//
final double lowerFrac = pseudoIndex - ((double) lowerIndex);
final double upperFrac = 1-lowerFrac;
// if the pseudo
if( SNAP_TOLERANCE > lowerFrac ){
// index ~= int ... therefore:
@ -460,8 +458,8 @@ public class ThrustCurveMotor implements Motor, Comparable<ThrustCurveMotor>, Se
final double lowerValue = values[lowerIndex];
final double upperValue = values[upperIndex];
// return simple linear interpolation
return ( lowerValue*lowerFrac + upperValue*upperFrac );
// return simple linear inverse interpolation
return ( lowerValue*upperFrac + upperValue*lowerFrac );
}

8
core/test/net/sf/openrocket/motor/ThrustCurveMotorTest.java
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@ -1,6 +1,7 @@
package net.sf.openrocket.motor;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;
import org.junit.Test;
@ -116,8 +117,11 @@ public class ThrustCurveMotorTest {
};
for( Pair<Double,Double> testCase : testPairs ){
final double time = testCase.getV();
final double motorTime = testCase.getV();
final double expThrust = testCase.getU();
final double actThrust = mtr.getThrust(motorTime);
assertEquals( "Error in interpolating thrust: ", expThrust, actThrust, 0.001 );
}
}
@ -133,7 +137,7 @@ public class ThrustCurveMotorTest {
public void testTimeIndexingNegative(){
final ThrustCurveMotor mtr = motorX6;
// attempt to retrieve for a time before the motor ignites
assertEquals( 0.0, mtr.getTime( -1 ), 0.00000001 );
assertTrue( "Fault in negative time indexing: ", Double.isNaN( mtr.getTime( -1 )) );
}
@Test