Merge pull request #505 from teyrana/fix_500_cg

[fixes #500] May Calculate CG for fins on zero-dimension mounts

core/src/net/sf/openrocket/rocketcomponent/FinSet.java

@@ -412,8 +412,12 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 				- outerArcAngle * filletRadius * filletRadius / 2
 				- innerArcAngle * bodyRadius * bodyRadius / 2);
 
-		// each fin has a fillet on each side
+		if(Double.isNaN(crossSectionArea)) {
-		crossSectionArea *= 2;
+			crossSectionArea = 0.;
+		}else {
+			// each fin has a fillet on each side
+			crossSectionArea *= 2;
+		}
 
 		// heuristic, relTo the body center
 		double yCentroid = bodyRadius + filletRadius /5;
@@ -435,28 +439,26 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 	 * 5. Return twice that since there is a fillet on each side of the fin.
 	 */
 	protected Coordinate calculateFilletVolumeCentroid() {
-		Coordinate[] bodyPoints = this.getBodyPoints();
+		Coordinate[] mountPoints = this.getRootPoints();
-		if (0 == bodyPoints.length) {
+		if( null == mountPoints ){
 			return Coordinate.ZERO;
 		}
-
+		
 		final SymmetricComponent sym = (SymmetricComponent) this.parent;
 		if (!SymmetricComponent.class.isInstance(this.parent)) {
 			return Coordinate.ZERO;
 		}
 
 		Coordinate filletVolumeCentroid = Coordinate.ZERO;
-
+		Coordinate prev = mountPoints[0];
-
+		for (int index = 1; index < mountPoints.length; index++) {
-		Coordinate prev = bodyPoints[0];
+			final Coordinate cur = mountPoints[index];
-		for (int index = 1; index < bodyPoints.length; index++) {
-			final Coordinate cur = bodyPoints[index];
 
 			// cross section at mid-segment
 			final double xAvg = (prev.x + cur.x) / 2;
 			final double bodyRadius = sym.getRadius(xAvg);
 			final Coordinate segmentCrossSection = calculateFilletCrossSection(this.filletRadius, bodyRadius).setX(xAvg);
-
+			
 //			final double xCentroid = xAvg;
 //			final double yCentroid = segmentCrossSection.y; ///< heuristic, not exact
 			final double segmentLength = Point2D.Double.distance(prev.x, prev.y, cur.x, cur.y);
@@ -468,10 +470,7 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 
 			prev = cur;
 		}
-
+		
-		// translate to be relative to the fin-lead-root
-		filletVolumeCentroid = filletVolumeCentroid.sub(getAxialFront(), 0,0);
-
 		if (finCount == 1) {
 			Transformation rotation = Transformation.rotate_x( getAngleOffset());
 			return rotation.transform(filletVolumeCentroid);
@@ -541,7 +540,7 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 		final double xTabTrail_body = xFinFront_body + xTabTrail_fin;
 				
 		// always returns x coordinates relTo fin front:
-		Coordinate[] upperCurve = getBodyPoints( xTabFront_body, xTabTrail_body );
+		Coordinate[] upperCurve = getMountInterval( xTabFront_body, xTabTrail_body );
 		// locate relative to fin/body centerline
 		upperCurve = translatePoints( upperCurve, -xFinFront_body, 0.0);
 		
@@ -572,15 +571,15 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 	 */
 	private Coordinate calculateSinglePlanformCentroid(){
 		final Coordinate finFront = getFinFront();
-
+		
-		final Coordinate[] upperCurve = translatePoints( getFinPoints(), finFront.x, finFront.y );
+		final Coordinate[] upperCurve = getFinPoints();
-		final Coordinate[] lowerCurve = getBodyPoints();
+		final Coordinate[] lowerCurve = getRootPoints();
 		final Coordinate[] totalCurve = combineCurves( upperCurve, lowerCurve);
-
+		
 		Coordinate planformCentroid = calculateCurveIntegral( totalCurve );
 
 		// return as a position relative to fin-root
-		return planformCentroid.sub(finFront.x,0,0);
+		return planformCentroid.add(0., finFront.y, 0);
 	}
 
 	/** 
@@ -1042,11 +1041,12 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 	 * 
 	 * @return points representing the fin-root points, relative to ( x: fin-front, y: centerline ) i.e. relto: fin Component reference point
 	 */
-	public Coordinate[] getBodyPoints() {
+	public Coordinate[] getMountPoints() {
-		final double xFinStart = getAxialFront();
+		if( null == parent){
-		final double xFinEnd = xFinStart+getLength();
+			return null;
-
+		}
-		return getBodyPoints( xFinStart, xFinEnd);
+		
+		return getMountInterval(0., parent.getLength());
 	}
 
 	/**
@@ -1055,19 +1055,22 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 	 * @return points representing the fin-root points, relative to ( x: fin-front, y: fin-root-radius ) 
 	 */
 	public Coordinate[] getRootPoints(){
-		final Coordinate finLead = getFinFront();
-		final double finTailX = finLead.x + getLength();
-
-		final Coordinate[] bodyPoints = getBodyPoints( finLead.x, finTailX);
-
-		return translatePoints(bodyPoints, -finLead.x, -finLead.y);
-	}
-
-	private Coordinate[] getBodyPoints( final double xStart, final double xEnd ) {
 		if( null == parent){
 			return new Coordinate[]{Coordinate.ZERO};
 		}
 		
+		final Coordinate finLead = getFinFront();
+		final double finTailX = finLead.x + getLength();
+
+		final Coordinate[] bodyPoints = getMountInterval( finLead.x, finTailX);
+
+		return translatePoints(bodyPoints, -finLead.x, -finLead.y);
+	}
+
+	
+	private Coordinate[] getMountInterval(  final double xStart, final double xEnd ) {
+//		System.err.println(String.format("    .... >> mount interval/x: ( %g, %g)]", xStart, xEnd));
+
 		// for a simple bodies, one increment is perfectly accurate.
 		int divisionCount = 1;
 		// cast-assert
@@ -1101,7 +1104,7 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 		if( body.getLength()-0.000001 < points[lastIndex].x) {
 			points[lastIndex] = points[lastIndex].setX(body.getLength()).setY(body.getAftRadius());
 		}
-
+		
 		return points;
 	}
 
@@ -1125,7 +1128,8 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 		buf.append( getPointDescr( this.getFinPoints(), "Fin Points", ""));
 
 		if (null != parent) {
-			buf.append( getPointDescr( this.getBodyPoints(), "Body Points", ""));
+			buf.append( getPointDescr( this.getRootPoints(), "Root Points", ""));
+			buf.append( getPointDescr( this.getMountPoints(), "Mount Points", ""));
 		}
 
 		if( ! this.isTabTrivial() ) {
@@ -1146,7 +1150,7 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 		final double tabVolume = tabCentroid.weight * thickness;
 		final double tabMass = tabVolume * material.getDensity();
 		final Coordinate tabCM = tabCentroid.setWeight(tabMass);
-
+		
 		Coordinate filletCentroid = calculateFilletVolumeCentroid();
 		double filletVolume = filletCentroid.weight;
 		double filletMass = filletVolume * filletMaterial.getDensity();
@@ -1156,7 +1160,7 @@ public abstract class FinSet extends ExternalComponent implements RingInstanceab
 
 		final double eachFinMass = finBulkMass + tabMass + filletMass;
 		final Coordinate eachFinCenterOfMass = wettedCM.average(tabCM).average(filletCM).setWeight(eachFinMass);
-
+		
 		// ^^ per fin
 		// vv per component
 

core/test/net/sf/openrocket/rocketcomponent/FreeformFinSetTest.java

@@ -1179,13 +1179,13 @@ public class FreeformFinSetTest extends BaseTestCase {
 		final Coordinate[] finPointsFromBody = FinSet.translatePoints( finPoints,  0.0, fins.getFinFront().y);
 
 		{ // body points (relative to body)
-			final Coordinate[] bodyPoints = fins.getBodyPoints();
+			final Coordinate[] mountPoints = fins.getMountPoints();
 	
-			assertEquals("Method should only generate minimal points for a conical transition fin body! ", 2, bodyPoints.length );
+			assertEquals("Method should only generate minimal points for a conical transition fin body! ", 2, mountPoints.length );
-			assertEquals("incorrect body points! ", finPointsFromBody[0].x, bodyPoints[0].x, EPSILON);
+			assertEquals("incorrect body points! ", finPointsFromBody[0].x, mountPoints[0].x, EPSILON);
-			assertEquals("incorrect body points! ", finPointsFromBody[0].y, bodyPoints[0].y, EPSILON);
+			assertEquals("incorrect body points! ", finPointsFromBody[0].y, mountPoints[0].y, EPSILON);
-			assertEquals("incorrect body points! ", finPointsFromBody[finPoints.length-1].x, bodyPoints[1].x, EPSILON);
+			assertEquals("incorrect body points! ", finPointsFromBody[finPoints.length-1].x, mountPoints[1].x, EPSILON);
-			assertEquals("incorrect body points! ", finPointsFromBody[finPoints.length-1].y, bodyPoints[1].y, EPSILON);
+			assertEquals("incorrect body points! ", finPointsFromBody[finPoints.length-1].y, mountPoints[1].y, EPSILON);
 		}
 		{ // root points (relative to fin-front)
 			final Coordinate[] rootPoints = fins.getRootPoints();
@@ -1203,18 +1203,16 @@ public class FreeformFinSetTest extends BaseTestCase {
 		final Rocket rkt = createTemplateRocket();
 		final FreeformFinSet fins = (FreeformFinSet) rkt.getChild(0).getChild(2).getChild(0);
 
-		final Coordinate finFront = fins.getFinFront();
 		final Coordinate[] finPoints = fins.getFinPoints();
-		final Coordinate[] finPointsFromBody = FinSet.translatePoints( finPoints,  finFront.x, finFront.y);
+		
-
 		{ // body points (relative to body)
-			final Coordinate[] bodyPoints = fins.getBodyPoints();
+			final Coordinate[] bodyPoints = fins.getMountPoints();
 
 			assertEquals("Method should only generate minimal points for a conical transition fin body! ", 2, bodyPoints.length );
-			assertEquals("incorrect body points! ", finPointsFromBody[0].x, bodyPoints[0].x, EPSILON);
+			assertEquals("incorrect body points! ", 0.0, bodyPoints[0].x, EPSILON);
-			assertEquals("incorrect body points! ", finPointsFromBody[0].y, bodyPoints[0].y, EPSILON);
+			assertEquals("incorrect body points! ", 1.0, bodyPoints[0].y, EPSILON);
-			assertEquals("incorrect body points! ", finPointsFromBody[finPoints.length-1].x, bodyPoints[1].x, EPSILON);
+			assertEquals("incorrect body points! ", 1.0, bodyPoints[1].x, EPSILON);
-			assertEquals("incorrect body points! ", finPointsFromBody[finPoints.length-1].y, bodyPoints[1].y, EPSILON);
+			assertEquals("incorrect body points! ", 0.5, bodyPoints[1].y, EPSILON);
 		}
 		{ // body points (relative to root)
 			final Coordinate[] rootPoints = fins.getRootPoints();
@@ -1236,7 +1234,6 @@ public class FreeformFinSetTest extends BaseTestCase {
 		final Coordinate finFront = fins.getFinFront();
 		final Coordinate[] finPoints = fins.getFinPoints();
 		
-		
 		{ // fin points (relative to fin) // preconditions
 			assertEquals(4, finPoints.length);
 			
@@ -1281,35 +1278,30 @@ public class FreeformFinSetTest extends BaseTestCase {
 			    }
 			}
 		}{ // body points (relative to body)
-			// translate from fin-frame to body-frame
+			final Coordinate[] mountPoints = fins.getMountPoints();
-			final Coordinate[] finPointsFromBody = FinSet.translatePoints( fins.getFinPoints(), finFront.x, finFront.y );
+			assertEquals(101, mountPoints.length);
 			
-			final Coordinate[] bodyPoints = fins.getBodyPoints();
-			assertEquals(101, bodyPoints.length);
-			
-			final Coordinate expectedEndPoint = finPointsFromBody[ finPoints.length-1];
-
 			// trivial, and uninteresting:
-			assertEquals("incorrect body points! ", finPointsFromBody[0].x, bodyPoints[0].x, EPSILON);
+			assertEquals("incorrect body points! ", 0.0, mountPoints[0].x, EPSILON);
-			assertEquals("incorrect body points! ", finPointsFromBody[0].y, bodyPoints[0].y, EPSILON);
+			assertEquals("incorrect body points! ", 0.0, mountPoints[0].y, EPSILON);
 	
 			// n.b.: This should match EXACTLY the end point of the fin. (in fin coordinates)
-			assertEquals("incorrect body points! ",  expectedEndPoint.x, bodyPoints[bodyPoints.length-1].x, EPSILON);
+			assertEquals("incorrect body points! ",  1.0, mountPoints[mountPoints.length-1].x, EPSILON);
-			assertEquals("incorrect body points! ",  expectedEndPoint.y, bodyPoints[bodyPoints.length-1].y, EPSILON);
+			assertEquals("incorrect body points! ",  1.0, mountPoints[mountPoints.length-1].y, EPSILON);
 	
 			{// the tests within this scope is are rather fragile, and may break for reasons other than bugs :(
 				// the number of points is somewhat arbitrary, but if this test fails, the rest *definitely* will.
-				assertEquals("Method is generating how many points, in general? ", 101, bodyPoints.length );
+				assertEquals("Method is generating how many points, in general? ", 101, mountPoints.length );
-	
-				final int[] testIndices = {  2,      5,     61,      88};
-				final double[] expectedX = { 0.036,  0.06,   0.508,   0.724};
 	
+				final int[] testIndices = {  3,     12,     61,    88};
+				final double[] expectedX = { 0.03,   0.12,   0.61,  0.88};
+
 				for( int testCase = 0; testCase < testIndices.length; testCase++){
 					final int testIndex =  testIndices[testCase];
 					assertEquals(String.format("Body points @ %d :: x coordinate mismatch!", testIndex),
-							expectedX[testCase], bodyPoints[testIndex].x, EPSILON);
+							expectedX[testCase], mountPoints[testIndex].x, EPSILON);
 					assertEquals(String.format("Body points @ %d :: y coordinate mismatch!", testIndex),
-							body.getRadius(bodyPoints[testIndex].x), bodyPoints[testIndex].y, EPSILON);
+							body.getRadius(mountPoints[testIndex].x), mountPoints[testIndex].y, EPSILON);
 			    }
 			}
 		}

core/test/net/sf/openrocket/rocketcomponent/TrapezoidFinSetTest.java

@@ -90,7 +90,7 @@ public class TrapezoidFinSetTest extends BaseTestCase {
 		final Rocket rkt = createSimpleTrapezoidalFin();
 		final TrapezoidFinSet fins = (TrapezoidFinSet)rkt.getChild(0).getChild(0).getChild(0);
 
-		// This is a simple square fin with sides of 1.0.
+		// This is a simple square fin with sides of 0.1.
 		fins.setFinShape(0.1, 0.1, 0.0, 0.1, .005);
 
 		// should return a single-fin-planform area
@@ -170,14 +170,14 @@ public class TrapezoidFinSetTest extends BaseTestCase {
 		//        /      \
 		//   [0] +--------+ [3]
 		//
+		assertEquals(0.06, fins.getLength(), EPSILON);
 		assertEquals("Body radius doesn't match: ", 0.1, body.getOuterRadius(), EPSILON);
 
 		final Coordinate actVolume = fins.calculateFilletVolumeCentroid();
 
-		assertEquals("Line volume doesn't match: ", 5.973e-07, actVolume.weight, EPSILON);
+		assertEquals("Fin volume doesn't match: ", 5.973e-07, actVolume.weight, EPSILON);
-
+		assertEquals("Fin mass center.x doesn't match: ", 0.03, actVolume.x, EPSILON);
-		assertEquals("Line mass center.x doesn't match: ", 0.03, actVolume.x, EPSILON);
+		assertEquals("Fin mass center.y doesn't match: ", 0.101, actVolume.y, EPSILON);
-		assertEquals("Line mass center.y doesn't match: ", 0.101, actVolume.y, EPSILON);
 
 
 		{ // and then, check that the fillet volume feeds into a correct overall CG:
@@ -189,7 +189,6 @@ public class TrapezoidFinSetTest extends BaseTestCase {
 
 	@Test
 	public void testTrapezoidCGComputation() {
-		
 		{
 			// This is a simple square fin with sides of 1.0.
 			TrapezoidFinSet fins = new TrapezoidFinSet();
@@ -200,9 +199,7 @@ public class TrapezoidFinSetTest extends BaseTestCase {
 			assertEquals(1.0, fins.getPlanformArea(), 0.001);
 			assertEquals(0.5, coords.x, 0.001);
 			assertEquals(0.5, coords.y, 0.001);
-		}
+		}{
-		
-		{
 			// This is a trapezoid.  Height 1, root 1, tip 1/2 no sweep.
 			// It can be decomposed into a rectangle followed by a triangle
 			//  +---+
@@ -218,7 +215,77 @@ public class TrapezoidFinSetTest extends BaseTestCase {
 			assertEquals(0.3889, coords.x, 0.001);
 			assertEquals(0.4444, coords.y, 0.001);
 		}
+	}
+	
+	@Test
+	public void testGetBodyPoints_phantomMount() {
+		final Rocket rkt = createSimpleTrapezoidalFin();
 		
+		// set mount to have zero-dimensions:
+		final BodyTube mount = (BodyTube)rkt.getChild(0).getChild(0);
+		mount.setLength(0.0);
+		mount.setOuterRadius(0.0);
+		assertEquals( 0, mount.getLength(), 0.00001);
+		assertEquals( 0, mount.getOuterRadius(), 0.00001);
+		assertEquals( 0, mount.getInnerRadius(), 0.00001);
+		
+		final TrapezoidFinSet fins = (TrapezoidFinSet)mount.getChild(0);
+		final Coordinate[] mountPoints = fins.getMountPoints();
+		
+		assertEquals(2, mountPoints.length );
+		assertEquals( 0.00, mountPoints[0].x, 0.00001);
+		assertEquals( 0.00, mountPoints[0].y, 0.00001);
+		assertEquals( 0.00, mountPoints[1].x, 0.00001);
+		assertEquals( 0.00, mountPoints[1].y, 0.00001);
+	}
+	
+	@Test
+	public void testGetBodyPoints_zeroLengthMount() {
+		final Rocket rkt = createSimpleTrapezoidalFin();
+		
+		// set mount to have zero-dimensions:
+		final BodyTube mount = (BodyTube)rkt.getChild(0).getChild(0);
+		mount.setLength(0.0);
+		mount.setOuterRadius(0.1);
+		mount.setInnerRadius(0.08);
+		assertEquals( 0, mount.getLength(), 0.00001);
+		assertEquals( 0.1, mount.getOuterRadius(), 0.00001);
+		assertEquals( 0.08, mount.getInnerRadius(), 0.00001);
+		
+		final TrapezoidFinSet fins = (TrapezoidFinSet)mount.getChild(0);
+		final Coordinate[] mountPoints = fins.getMountPoints();
+				
+		assertEquals(2, mountPoints.length );
+		assertEquals( 0.0, mountPoints[0].x, 0.00001);
+		assertEquals( 0.1, mountPoints[0].y, 0.00001);
+		assertEquals( 0.0, mountPoints[1].x, 0.00001);
+		assertEquals( 0.1, mountPoints[1].y, 0.00001);
+	}
+	
+	@Test
+	public void testTrapezoidCGComputation_phantomMount() {
+		final Rocket rkt = createSimpleTrapezoidalFin();
+		
+		// set mount to have zero-dimensions:
+		final BodyTube mount = (BodyTube)rkt.getChild(0).getChild(0);
+		mount.setLength(0.0);
+		mount.setOuterRadius(0.0);
+
+		assertEquals( 0, mount.getLength(), 0.00001);
+		assertEquals( 0, mount.getOuterRadius(), 0.00001);
+		assertEquals( 0, mount.getInnerRadius(), 0.00001);
+		
+		final TrapezoidFinSet fins = (TrapezoidFinSet)mount.getChild(0);
+		
+		assertEquals( 0.06, fins.getLength(), 0.00001);
+		assertEquals( 0.05, fins.getHeight(), 0.00001);
+		assertEquals( 0.06, fins.getRootChord(), 0.00001);
+		assertEquals( 0.02, fins.getTipChord(), 0.00001);
+		
+		final Coordinate coords = fins.getCG();
+		assertEquals(0.002, fins.getPlanformArea(), 0.001);
+		assertEquals(0.03, coords.x, 0.001);
+		assertEquals(0.02, coords.y, 0.001);
 	}
 	
 	@Test