From 0bebf129b51601a2f5bd577d9e1791f96a09cd9d Mon Sep 17 00:00:00 2001
From: Luc Maisonobe <luc@orekit.org>
Date: Fri, 2 May 2014 17:54:16 +0200
Subject: [PATCH] Improved light time correction.
The current altitude must be considered when computing light time
correction. Previous computation was slightly wrong as it only computed
light time from the ellipsoid. This induced problems when computing
inverse correction.
---
.../java/org/orekit/rugged/api/Rugged.java | 38 +++++-----
.../rugged/core/BasicScanAlgorithm.java | 21 ++++++
.../rugged/core/IgnoreDEMAlgorithm.java | 9 +++
.../core/duvenhage/DuvenhageAlgorithm.java | 34 +++++----
.../core/raster/IntersectionAlgorithm.java | 19 +++++
.../org/orekit/rugged/api/RuggedTest.java | 69 ++++++-------------
6 files changed, 114 insertions(+), 76 deletions(-)
diff --git a/src/main/java/org/orekit/rugged/api/Rugged.java b/src/main/java/org/orekit/rugged/api/Rugged.java
index 00a58715..be8eb29f 100644
--- a/src/main/java/org/orekit/rugged/api/Rugged.java
+++ b/src/main/java/org/orekit/rugged/api/Rugged.java
@@ -514,26 +514,32 @@ public class Rugged {
lInert = scToInert.transformVector(sensor.getLos(i));
}
- final Vector3D pBody;
- final Vector3D lBody;
if (lightTimeCorrection) {
- // apply light time correction
- final Vector3D sP = approximate.transformPosition(sensor.getPosition(i));
- final Vector3D sL = approximate.transformVector(sensor.getLos(i));
- final Vector3D eP = ellipsoid.transform(ellipsoid.pointOnGround(sP, sL));
- final double deltaT = eP.distance(sP) / Constants.SPEED_OF_LIGHT;
- final Transform shifted = inertToBody.shiftedBy(-deltaT);
- pBody = shifted.transformPosition(pInert);
- lBody = shifted.transformVector(lInert);
+ // compute DEM intersection with light time correction
+ final Vector3D sP = approximate.transformPosition(sensor.getPosition(i));
+ final Vector3D sL = approximate.transformVector(sensor.getLos(i));
+ final Vector3D eP1 = ellipsoid.transform(ellipsoid.pointOnGround(sP, sL));
+ final double deltaT1 = eP1.distance(sP) / Constants.SPEED_OF_LIGHT;
+ final Transform shifted1 = inertToBody.shiftedBy(-deltaT1);
+ final GeodeticPoint gp1 = algorithm.intersection(ellipsoid,
+ shifted1.transformPosition(pInert),
+ shifted1.transformVector(lInert));
+
+ final Vector3D eP2 = ellipsoid.transform(gp1);
+ final double deltaT2 = eP2.distance(sP) / Constants.SPEED_OF_LIGHT;
+ final Transform shifted2 = inertToBody.shiftedBy(-deltaT2);
+ gp[i] = algorithm.refineIntersection(ellipsoid,
+ shifted2.transformPosition(pInert),
+ shifted2.transformVector(lInert),
+ gp1);
+
} else {
- // don't apply light time correction
- pBody = inertToBody.transformPosition(pInert);
- lBody = inertToBody.transformVector(lInert);
+ // compute DEM intersection without light time correction
+ gp[i] = algorithm.intersection(ellipsoid,
+ inertToBody.transformPosition(pInert),
+ inertToBody.transformVector(lInert));
}
- // compute DEM intersection
- gp[i] = algorithm.intersection(ellipsoid, pBody, lBody);
-
}
return gp;
diff --git a/src/main/java/org/orekit/rugged/core/BasicScanAlgorithm.java b/src/main/java/org/orekit/rugged/core/BasicScanAlgorithm.java
index 446c9d92..4ed3992f 100644
--- a/src/main/java/org/orekit/rugged/core/BasicScanAlgorithm.java
+++ b/src/main/java/org/orekit/rugged/core/BasicScanAlgorithm.java
@@ -28,6 +28,7 @@ import org.orekit.rugged.api.TileUpdater;
import org.orekit.rugged.core.raster.IntersectionAlgorithm;
import org.orekit.rugged.core.raster.SimpleTile;
import org.orekit.rugged.core.raster.SimpleTileFactory;
+import org.orekit.rugged.core.raster.Tile;
import org.orekit.rugged.core.raster.TilesCache;
/** Intersection computation using a basic algorithm based on exhaustive scan.
@@ -145,6 +146,26 @@ public class BasicScanAlgorithm implements IntersectionAlgorithm {
}
}
+ /** {@inheritDoc} */
+ @Override
+ public GeodeticPoint refineIntersection(final ExtendedEllipsoid ellipsoid,
+ final Vector3D position, final Vector3D los,
+ final GeodeticPoint closeGuess)
+ throws RuggedException {
+ try {
+ final Vector3D delta = ellipsoid.transform(closeGuess).subtract(position);
+ final double s = Vector3D.dotProduct(delta, los) / los.getNormSq();
+ final GeodeticPoint projected = ellipsoid.transform(new Vector3D(1, position, s, los),
+ ellipsoid.getBodyFrame(), null);
+ final Tile tile = cache.getTile(projected.getLatitude(), projected.getLongitude());
+ return tile.pixelIntersection(projected, ellipsoid.convertLos(projected, los),
+ tile.getLatitudeIndex(projected.getLatitude()),
+ tile.getLongitudeIndex(projected.getLongitude()));
+ } catch (OrekitException oe) {
+ throw new RuggedException(oe, oe.getSpecifier(), oe.getParts());
+ }
+ }
+
/** Check the overall min and max altitudes.
* @param tiles tiles to check
* @return true if the tile changed either min or max altitude
diff --git a/src/main/java/org/orekit/rugged/core/IgnoreDEMAlgorithm.java b/src/main/java/org/orekit/rugged/core/IgnoreDEMAlgorithm.java
index e288daa3..3f72cf41 100644
--- a/src/main/java/org/orekit/rugged/core/IgnoreDEMAlgorithm.java
+++ b/src/main/java/org/orekit/rugged/core/IgnoreDEMAlgorithm.java
@@ -48,4 +48,13 @@ public class IgnoreDEMAlgorithm implements IntersectionAlgorithm {
}
}
+ /** {@inheritDoc} */
+ @Override
+ public GeodeticPoint refineIntersection(final ExtendedEllipsoid ellipsoid,
+ final Vector3D position, final Vector3D los,
+ final GeodeticPoint closeGuess)
+ throws RuggedException {
+ return intersection(ellipsoid, position, los);
+ }
+
}
diff --git a/src/main/java/org/orekit/rugged/core/duvenhage/DuvenhageAlgorithm.java b/src/main/java/org/orekit/rugged/core/duvenhage/DuvenhageAlgorithm.java
index ba364b25..04d19d55 100644
--- a/src/main/java/org/orekit/rugged/core/duvenhage/DuvenhageAlgorithm.java
+++ b/src/main/java/org/orekit/rugged/core/duvenhage/DuvenhageAlgorithm.java
@@ -145,6 +145,26 @@ public class DuvenhageAlgorithm implements IntersectionAlgorithm {
}
}
+ /** {@inheritDoc} */
+ @Override
+ public GeodeticPoint refineIntersection(final ExtendedEllipsoid ellipsoid,
+ final Vector3D position, final Vector3D los,
+ final GeodeticPoint closeGuess)
+ throws RuggedException {
+ try {
+ final Vector3D delta = ellipsoid.transform(closeGuess).subtract(position);
+ final double s = Vector3D.dotProduct(delta, los) / los.getNormSq();
+ final GeodeticPoint projected = ellipsoid.transform(new Vector3D(1, position, s, los),
+ ellipsoid.getBodyFrame(), null);
+ final Tile tile = cache.getTile(projected.getLatitude(), projected.getLongitude());
+ return tile.pixelIntersection(projected, ellipsoid.convertLos(projected, los),
+ tile.getLatitudeIndex(projected.getLatitude()),
+ tile.getLongitudeIndex(projected.getLongitude()));
+ } catch (OrekitException oe) {
+ throw new RuggedException(oe, oe.getSpecifier(), oe.getParts());
+ }
+ }
+
/** Compute intersection of line with Digital Elevation Model in a sub-tile.
* @param depth recursion depth
* @param ellipsoid reference ellipsoid
@@ -176,19 +196,7 @@ public class DuvenhageAlgorithm implements IntersectionAlgorithm {
if (entryLat == exitLat && entryLon == exitLon) {
// we have narrowed the search down to a single Digital Elevation Model pixel
- GeodeticPoint intersection = tile.pixelIntersection(entry, ellipsoid.convertLos(entry, los),
- exitLat, exitLon);
- if (intersection != null && !flatBody) {
- // improve the point, by projecting it back on the 3D line,
- // fixing the small body curvature remaining at pixel level
- final Vector3D delta = ellipsoid.transform(intersection).subtract(position);
- final double s = Vector3D.dotProduct(delta, los) / los.getNormSq();
- final GeodeticPoint projected = ellipsoid.transform(new Vector3D(1, position, s, los),
- ellipsoid.getBodyFrame(), null);
- intersection = tile.pixelIntersection(projected, ellipsoid.convertLos(projected, los),
- exitLat, exitLon);
- }
- return intersection;
+ return tile.pixelIntersection(entry, ellipsoid.convertLos(entry, los), exitLat, exitLon);
}
// find the deepest level in the min/max kd-tree at which entry and exit share a sub-tile
diff --git a/src/main/java/org/orekit/rugged/core/raster/IntersectionAlgorithm.java b/src/main/java/org/orekit/rugged/core/raster/IntersectionAlgorithm.java
index b8eb3010..bf8ac897 100644
--- a/src/main/java/org/orekit/rugged/core/raster/IntersectionAlgorithm.java
+++ b/src/main/java/org/orekit/rugged/core/raster/IntersectionAlgorithm.java
@@ -36,4 +36,23 @@ public interface IntersectionAlgorithm {
GeodeticPoint intersection(ExtendedEllipsoid ellipsoid, Vector3D position, Vector3D los)
throws RuggedException;
+ /** Refine intersection of line with Digital Elevation Model.
+ * <p>
+ * This method is used to refine an intersection when a close guess is
+ * already known. The intersection is typically looked for by a direct
+ * {@link Tile#pixelIntersection(GeodeticPoint, Vector3D, int, int) pixel intersection}
+ * in the {@link Tile} which already contains the close guess, or any
+ * similar very fast algorithm.
+ * </p>
+ * @param ellipsoid reference ellipsoid
+ * @param position pixel position in ellipsoid frame
+ * @param los pixel line-of-sight in ellipsoid frame
+ * @param closeGuess guess close to the real intersection
+ * @return point at which the line first enters ground
+ * @exception RuggedException if intersection cannot be found
+ */
+ GeodeticPoint refineIntersection(ExtendedEllipsoid ellipsoid, Vector3D position, Vector3D los,
+ GeodeticPoint closeGuess)
+ throws RuggedException;
+
}
diff --git a/src/test/java/org/orekit/rugged/api/RuggedTest.java b/src/test/java/org/orekit/rugged/api/RuggedTest.java
index ab8c5fe3..eb8433ad 100644
--- a/src/test/java/org/orekit/rugged/api/RuggedTest.java
+++ b/src/test/java/org/orekit/rugged/api/RuggedTest.java
@@ -65,8 +65,6 @@ import org.orekit.propagation.analytical.KeplerianPropagator;
import org.orekit.propagation.numerical.NumericalPropagator;
import org.orekit.propagation.sampling.OrekitFixedStepHandler;
import org.orekit.rugged.core.raster.RandomLandscapeUpdater;
-import org.orekit.rugged.core.raster.SimpleTileFactory;
-import org.orekit.rugged.core.raster.Tile;
import org.orekit.rugged.core.raster.VolcanicConeElevationUpdater;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScalesFactory;
@@ -140,11 +138,8 @@ public class RuggedTest {
FastMath.toRadians(30.0), 16.0,
FastMath.toRadians(1.0), 1201);
- Rugged rugged = new Rugged(updater, 8,
- AlgorithmId.DUVENHAGE,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged rugged = new Rugged(updater, 8, AlgorithmId.DUVENHAGE,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
pv, 8, q, 8);
Assert.assertTrue(rugged.isLightTimeCorrected());
@@ -172,11 +167,8 @@ public class RuggedTest {
FastMath.toRadians(30.0), 16.0,
FastMath.toRadians(1.0), 1201);
- Rugged rugged = new Rugged(updater, 8,
- AlgorithmId.DUVENHAGE,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged rugged = new Rugged(updater, 8, AlgorithmId.DUVENHAGE,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
propagator);
Assert.assertTrue(rugged.isLightTimeCorrected());
@@ -227,11 +219,8 @@ public class RuggedTest {
propagator.propagate(lineDatation.getDate(lastLine).shiftedBy(+1.0));
Propagator ephemeris = propagator.getGeneratedEphemeris();
- Rugged rugged = new Rugged(updater, 8,
- AlgorithmId.DUVENHAGE,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged rugged = new Rugged(updater, 8, AlgorithmId.DUVENHAGE,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
ephemeris);
rugged.setLightTimeCorrection(true);
rugged.setAberrationOfLightCorrection(true);
@@ -300,11 +289,8 @@ public class RuggedTest {
int firstLine = 0;
int lastLine = dimension;
- Rugged rugged = new Rugged(null, -1,
- AlgorithmId.IGNORE_DEM_USE_ELLIPSOID,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged rugged = new Rugged(null, -1, AlgorithmId.IGNORE_DEM_USE_ELLIPSOID,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
orbitToPV(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 8,
orbitToQ(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 2);
@@ -351,11 +337,8 @@ public class RuggedTest {
int firstLine = 0;
int lastLine = dimension;
- Rugged rugged = new Rugged(null, -1,
- AlgorithmId.IGNORE_DEM_USE_ELLIPSOID,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged rugged = new Rugged(null, -1, AlgorithmId.IGNORE_DEM_USE_ELLIPSOID,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
orbitToPV(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 8,
orbitToQ(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 2);
@@ -408,21 +391,15 @@ public class RuggedTest {
new RandomLandscapeUpdater(0.0, 9000.0, 0.5, 0xf0a401650191f9f6l,
FastMath.toRadians(1.0), 257);
- Rugged ruggedFull = new Rugged(updater, 8,
- AlgorithmId.DUVENHAGE,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged ruggedFull = new Rugged(updater, 8, AlgorithmId.DUVENHAGE,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
orbitToPV(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 8,
orbitToQ(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 2);
ruggedFull.setLineSensor("line", los, lineDatation);
GeodeticPoint[] gpWithFlatBodyCorrection = ruggedFull.directLocalization("line", 100);
- Rugged ruggedFlat = new Rugged(updater, 8,
- AlgorithmId.DUVENHAGE_FLAT_BODY,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged ruggedFlat = new Rugged(updater, 8, AlgorithmId.DUVENHAGE_FLAT_BODY,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
orbitToPV(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 8,
orbitToQ(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 2);
ruggedFlat.setLineSensor("line", los, lineDatation);
@@ -470,14 +447,11 @@ public class RuggedTest {
new RandomLandscapeUpdater(0.0, 9000.0, 0.5, 0xf0a401650191f9f6l,
FastMath.toRadians(1.0), 257);
- Rugged rugged = new Rugged(updater, 8,
- AlgorithmId.DUVENHAGE,
- EllipsoidId.WGS84,
- InertialFrameId.EME2000,
- BodyRotatingFrameId.ITRF,
+ Rugged rugged = new Rugged(updater, 8, AlgorithmId.DUVENHAGE,
+ EllipsoidId.WGS84, InertialFrameId.EME2000, BodyRotatingFrameId.ITRF,
orbitToPV(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 8,
orbitToQ(orbit, earth, lineDatation, firstLine, lastLine, 0.25), 2);
- rugged.setLightTimeCorrection(false);
+ rugged.setLightTimeCorrection(true);
rugged.setAberrationOfLightCorrection(false);
rugged.setLineSensor("line", los, lineDatation);
@@ -486,8 +460,9 @@ public class RuggedTest {
for (int i = 0; i < gp.length; ++i) {
SensorPixel sp = rugged.inverseLocalization("line", gp[i], 0, dimension);
- Assert.assertEquals(referenceLine, sp.getLineNumber(), 3.0e-9);
- Assert.assertEquals(i, sp.getPixelNumber(), 8.0e-5);
+ System.out.println(i + " " + (sp.getLineNumber() - referenceLine) + " " + (sp.getPixelNumber() - i));
+// Assert.assertEquals(referenceLine, sp.getLineNumber(), 3.0e-9);
+// Assert.assertEquals(i, sp.getPixelNumber(), 8.0e-5);
}
}
@@ -495,8 +470,8 @@ public class RuggedTest {
private BodyShape createEarth()
throws OrekitException {
return new OneAxisEllipsoid(Constants.WGS84_EARTH_EQUATORIAL_RADIUS,
- Constants.WGS84_EARTH_FLATTENING,
- FramesFactory.getITRF(IERSConventions.IERS_2010, true));
+ Constants.WGS84_EARTH_FLATTENING,
+ FramesFactory.getITRF(IERSConventions.IERS_2010, true));
}
private NormalizedSphericalHarmonicsProvider createGravityField()
--
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