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Re: [Orekit Users] orekit and Jython

Petrus Hyvönen <petrus.hyvonen@gmail.com> a écrit :


Hi all,


Hi Petrus,
I was playing around with the idea of using Python for mission design, and found Jython and the orekit library. As new to both Python and Java, I had some initial troubles of getting things to work, primary the access to orekit-data, what was current dir and javapaths etc. I am now using Eclipse with pydev extension, and can add the orekit jars and orekit-data to the eclipse project.
As an exercise I took the liberty to translate a few of the orekit examples from java to jython, and copy them below as it could be of interest for others. I have been exploring scipy before (based on regular python) and it contains very good plotting and array routines, which is not available in jython. So next step would be to find a suitable java plotting and arrays library to be able to represent the results.
While answering to the next message in this thread, I noticed I forgot to answer you, I'm sorry for that. 

First I thank you very much for this contribution.
Concerning Java plotting, I'll suggest something like jfreechart (<http://www.jfree.org/jfreechart/>) which we have used extensively. It is also free software, but beware the license terms are different from Orekit or Apache Commons Math. JFreechart is a distributed under the terms of LGPL (which is a weak copyleft type license). 

Luc



Regards
/Petrus

First, a jython translation of the SlaveMode.java:
__________________________________________

# -*- coding: utf-8 -*-
'''
/* Copyright 2002-2010 CS Communication & Systèmes
 * Licensed to CS Communication & Systèmes (CS) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * CS licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

Translated from SlaveMode.java to jython by Petrus Hyvönen 2011-05-04
'''
# orekit.jar,orekit-data.zip and commons-maths in CLASSPATH through eclipse project 
import java, os

from org.orekit.errors import OrekitException
from org.orekit.frames import Frame
from org.orekit.frames import FramesFactory
from org.orekit.orbits import KeplerianOrbit
from org.orekit.orbits import Orbit
from org.orekit.propagation import SpacecraftState
from org.orekit.propagation.analytical import KeplerianPropagator
from org.orekit.data import DataProvidersManager
from org.orekit.data import ZipJarCrawler
from org.orekit.time import AbsoluteDate
from org.orekit.time import TimeScalesFactory

from math import radians

# Configure Orekit. The file orekit-data.zip must be in current dir
DM = DataProvidersManager.getInstance()
crawler=ZipJarCrawler("orekit-data.zip")
DM.clearProviders()
DM.addProvider(crawler)

#Initial orbit parameters
a = 24396159    # semi major axis in meters
e = 0.72831215  # eccentricity
i = radians(7.0)# inclination
omega = radians(180) # perigee argument
raan = radians(261) #right ascension of ascending node
lM = 0.0 # mean anomaly

#Inertial frame
inertialFrame = FramesFactory.getEME2000()

#Initial date in UTC time scale
utc = TimeScalesFactory.getUTC();
initialDate = AbsoluteDate(2004, 01, 01, 23, 30, 00.000, utc)

#gravitation coefficient
mu =  3.986004415e+14

#Orbit construction as Keplerian
initialOrbit = KeplerianOrbit(a, e, i, omega, raan, lM,
                              KeplerianOrbit.MEAN_ANOMALY,
                              inertialFrame, initialDate, mu)

#Simple extrapolation with Keplerian motion
kepler = KeplerianPropagator(initialOrbit)
#Set the propagator to slave mode (could be omitted as it is the default mode) 
kepler.setSlaveMode()

#Overall duration in seconds for extrapolation
duration = 90*60.0

#Stop date
finalDate =  AbsoluteDate(initialDate, duration, utc)

#Step duration in seconds
stepT = 30.0

#Extrapolation loop
cpt = 1
extrapDate = initialDate
while extrapDate.compareTo(finalDate) <= 0:
    currentState = kepler.propagate(extrapDate)
print "step %d: time %s %s" % (cpt, currentState.getDate(), currentState.getOrbit()) 
    extrapDate = AbsoluteDate(extrapDate, stepT, utc)
    cpt=cpt+1


____________________________

An interesting example of jython inheritance of java class:
_____________________________


# -*- coding: utf-8 -*-
'''
/* Copyright 2002-2010 CS Communication & Syst?mes
 * Licensed to CS Communication & Syst?mes (CS) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * CS licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

Translated from SlaveMode.java to jython by Petrus Hyv?nen 2011-05-04
'''
# orekit and common maths in CLASSPATH through eclipse project
import java, os

from org.orekit.data import DataProvidersManager
from org.orekit.data import ZipJarCrawler
from org.apache.commons.math.geometry import Vector3D
from org.orekit.bodies import BodyShape
from org.orekit.bodies import GeodeticPoint
from org.orekit.bodies import OneAxisEllipsoid
from org.orekit.errors import OrekitException;
from org.orekit.frames import Frame
from org.orekit.frames import FramesFactory
from org.orekit.frames import TopocentricFrame
from org.orekit.orbits import KeplerianOrbit
from org.orekit.orbits import Orbit
from org.orekit.propagation import Propagator
from org.orekit.propagation import SpacecraftState
from org.orekit.propagation.analytical import KeplerianPropagator
from org.orekit.propagation.events import ElevationDetector
from org.orekit.propagation.events import EventDetector
from org.orekit.time import AbsoluteDate
from org.orekit.time import TimeScalesFactory
from org.orekit.utils import PVCoordinates

from math import degrees, radians, pi

# Configure Orekit
DM = DataProvidersManager.getInstance()
crawler=ZipJarCrawler("orekit-data.zip")
DM.clearProviders()
DM.addProvider(crawler)

# Initial state definition: date, orbit
initialDate = AbsoluteDate(2004, 01, 01, 23, 30, 00.000, TimeScalesFactory.getUTC()) 
mu =  3.986004415e+14
inertialFrame = FramesFactory.getEME2000() # inertial frame for orbit definition 
position  = Vector3D(-6142438.668, 3492467.560, -25767.25680)
velocity  = Vector3D(505.8479685, 942.7809215, 7435.922231)
pvCoordinates = PVCoordinates(position, velocity)
initialOrbit = KeplerianOrbit(pvCoordinates, inertialFrame, initialDate, mu)

# Propagator : consider a simple keplerian motion (could be more elaborate)
kepler = KeplerianPropagator(initialOrbit)

#Earth and frame
ae =  6378137.0 # // equatorial radius in meter
f  =  1.0 / 298.257223563 #; // flattening
ITRF2005 = FramesFactory.getITRF2005() #; // terrestrial frame at an arbitrary date 
earth = OneAxisEllipsoid(ae, f, ITRF2005)

# Station
longitude = radians(45.0)
latitude  = radians(25.0)
altitude  = 0.0
station1 = GeodeticPoint(latitude, longitude, altitude)
sta1Frame = TopocentricFrame(earth, station1, "station1")

# Event definition
maxcheck  = 1.0
elevation = radians(5.0)


class VisibilityDetector(ElevationDetector):
# Class for handling the eventOccured java. Example of subclassing
# a java class in jython
    def __init__(self,  maxCheck,  elevation, topo):
        ElevationDetector.__init__(self,maxCheck, elevation, topo)

    def eventOccurred(self, s, increasing):
        if (increasing):
print "Visibility on", self.topocentricFrame.getName(),"begins at" , s.getDate() 
        else:
print "Visibility on", self.topocentricFrame.getName(), "ends at" , s.getDate() 
        return self.CONTINUE

sta1Visi = VisibilityDetector(maxcheck, elevation, sta1Frame)

#Add event to be detected
kepler.addEventDetector(sta1Visi)
#Propagate from the initial date to the first raising or for the fixed duration 
finalState = kepler.propagate(initialDate.shiftedBy(1500.0))

print "Final state : " , finalState.getDate().durationFrom(initialDate)

_________________________________







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