From 43bb8fd83a383affadb55c631c85943f183040f7 Mon Sep 17 00:00:00 2001
From: Luc Maisonobe <luc@orekit.org>
Date: Wed, 2 Apr 2014 11:21:44 +0200
Subject: [PATCH] Improved accuracy by taking speed of light into account in
transforms.
---
.../org/orekit/rugged/core/RuggedImpl.java | 20 ++++++++---
.../rugged/core/SpacecraftToObservedBody.java | 34 +++++++++++--------
2 files changed, 35 insertions(+), 19 deletions(-)
diff --git a/src/main/java/org/orekit/rugged/core/RuggedImpl.java b/src/main/java/org/orekit/rugged/core/RuggedImpl.java
index 7f52151d..c0625db0 100644
--- a/src/main/java/org/orekit/rugged/core/RuggedImpl.java
+++ b/src/main/java/org/orekit/rugged/core/RuggedImpl.java
@@ -374,17 +374,27 @@ public class RuggedImpl implements Rugged {
// select the sensor
final Sensor sensor = getSensor(sensorName);
- // compute once the transform between spacecraft and observed body
- final AbsoluteDate date = sensor.getDate(lineNumber);
- final Transform t = scToBody.getTransform(date);
+ // compute the approximate transform between spacecraft and observed body
+ final AbsoluteDate date = sensor.getDate(lineNumber);
+ final Transform scToInert = scToBody.getScToInertial(date);
+ final Transform inertToBody = scToBody.getInertialToBody(date);
+ final Transform approximate = new Transform(date, scToInert, inertToBody);
// compute localization of each pixel
final GroundPoint[] gp = new GroundPoint[sensor.getNbPixels()];
for (int i = 0; i < gp.length; ++i) {
+
+ // fix light travel time
+ 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 fixed = new Transform(date, scToInert, inertToBody.shiftedBy(-deltaT));
+
final GeodeticPoint geodetic =
algorithm.intersection(ellipsoid,
- t.transformPosition(sensor.getPosition(i)),
- t.transformVector(sensor.getLos(i)));
+ fixed.transformPosition(sensor.getPosition(i)),
+ fixed.transformVector(sensor.getLos(i)));
gp[i] = new GroundPoint(geodetic.getLatitude(),
geodetic.getLongitude(),
geodetic.getAltitude());
diff --git a/src/main/java/org/orekit/rugged/core/SpacecraftToObservedBody.java b/src/main/java/org/orekit/rugged/core/SpacecraftToObservedBody.java
index 5ec98eec..044471c8 100644
--- a/src/main/java/org/orekit/rugged/core/SpacecraftToObservedBody.java
+++ b/src/main/java/org/orekit/rugged/core/SpacecraftToObservedBody.java
@@ -21,18 +21,14 @@ import org.orekit.attitudes.AttitudeProvider;
import org.orekit.errors.OrekitException;
import org.orekit.frames.Frame;
import org.orekit.frames.Transform;
-import org.orekit.frames.TransformProvider;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.PVCoordinatesProvider;
-/** Transform provider from Spacecraft frame to observed body frame.
+/** Provider for observation transforms.
* @author Luc Maisonobe
*/
-class SpacecraftToObservedBody implements TransformProvider {
-
- /** Serializable UID. */
- private static final long serialVersionUID = 20140311L;
+class SpacecraftToObservedBody {
/** Inertial frame. */
private Frame inertialFrame;
@@ -61,9 +57,12 @@ class SpacecraftToObservedBody implements TransformProvider {
this.aProvider = aProvider;
}
- /** {@inheritDoc} */
- @Override
- public Transform getTransform(final AbsoluteDate date)
+ /** Get transform from spacecraft to inertial frame.
+ * @param date date of the transform
+ * @return transform from spacecraft to inertial frame
+ * @exception OrekitException if spacecraft position or attitude cannot be computed at date
+ */
+ public Transform getScToInertial(final AbsoluteDate date)
throws OrekitException {
// propagate/interpolate orbit and attitude
@@ -71,15 +70,22 @@ class SpacecraftToObservedBody implements TransformProvider {
final Attitude attitude = aProvider.getAttitude(pvProvider, date, inertialFrame);
// compute transform from spacecraft frame to inertial frame
- final Transform scToInert = new Transform(date,
+ return new Transform(date,
new Transform(date, attitude.getOrientation().revert()),
new Transform(date, pv));
- // compute transform from inertial frame to body frame
- final Transform inertToBody = inertialFrame.getTransformTo(bodyFrame, date);
+ }
- // combine transforms
- return new Transform(date, scToInert, inertToBody);
+ /** Get transform from inertial frame to body frame.
+ * @param date date of the transform
+ * @return transform from inertial frame to body frame
+ * @exception OrekitException if frames cannot be computed at date
+ */
+ public Transform getInertialToBody(final AbsoluteDate date)
+ throws OrekitException {
+
+ // compute transform from inertial frame to body frame
+ return inertialFrame.getTransformTo(bodyFrame, date);
}
--
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