DEIMOS
Earth Observation Mission CFI Software
Pointing Software User Manual
for JAVA
ESA

Earth Observation Mission CFI Software
POINTING SOFTWARE USER MANUAL
for JAVA
Code EO-MA-DMS-GS-025
Issue 4.27
Date 07/06/24
  Name Function Signature
Prepared by: EOCFI Team Project Engineers  
Checked by: Inês Estrela Project Manager  
Approved by: Antonio Gutierrez Division Head  

DOCUMENT INFORMATION

Contract Data Classification
Contract Number: 4000102614/1O/NL/FF/ef Internal  
Public  
Contract Issuer: ESA / ESTEC Industry X
Confidential  
External Distribution
Name Organization Copies
     
Electronic handling
Document generator: Doxygen 1.7.1
Electronic file name: eo-ma-dms-gs-015-10

Document Status Log

Issue Change Description Date Approval
1.0 These libraries corresponds to version 4.0 of C libraries. 22/06/09  
4.1 These libraries corresponds to version 4.1 of C libraries. 07/05/10  
4.2 These libraries corresponds to version 4.2 of C libraries. 31/01/11  
4.3 These libraries corresponds to version 4.3 of C libraries. 06/02/12  
4.4 These libraries corresponds to version 4.4 of C libraries. 05/07/12  
4.5 These libraries corresponds to version 4.5 of C libraries. 01/03/13  
4.6 These libraries corresponds to version 4.6 of C libraries. 03/10/13  
4.7 These libraries corresponds to version 4.7 of C libraries. 28/03/14  
4.8 These libraries corresponds to version 4.8 of C libraries. 29/10/14  
4.9 These libraries corresponds to version 4.9 of C libraries. 23/04/15  
4.10 These libraries corresponds to version 4.10 of C libraries. 29/10/15  
4.11 These libraries corresponds to version 4.11 of C libraries. 15/04/16  
4.12 These libraries corresponds to version 4.12 of C libraries. 03/11/16  
4.13 These libraries corresponds to version 4.13 of C libraries. 05/04/17  
4.14 These libraries corresponds to version 4.14 of C libraries. 16/11/17  
4.15 These libraries corresponds to version 4.15 of C libraries. 20/04/18  
4.16 These libraries corresponds to version 4.16 of C libraries. 09/11/18  
4.17 These libraries corresponds to version 4.17 of C libraries. 10/05/19  
4.18 These libraries corresponds to version 4.18 of C libraries. 08/11/19  
4.19 These libraries corresponds to version 4.19 of C libraries. 29/05/20  
4.20 These libraries corresponds to version 4.20 of C libraries. 30/11/20  
4.21 These libraries corresponds to version 4.21 of C libraries. 23/06/21  
4.22 These libraries corresponds to version 4.22 of C libraries. 22/12/21  
4.23 These libraries corresponds to version 4.23 of C libraries. 23/06/22  
4.24 These libraries corresponds to version 4.24 of C libraries. 29/11/22  
4.25 These libraries corresponds to version 4.25 of C libraries. 10/05/23  
4.26 These libraries corresponds to version 4.26 of C libraries. 31/10/23  
4.27 These libraries corresponds to version 4.27 of C libraries. 07/06/24

 


ACRONYMS, NOMENCLATURE AND TERMINOLOGY

Acronyms

ANX Ascending Node Crossing
AOCS Attitude and Orbit Control Subsystem
ASCII American Standard Code for Information Interchange
CFI Customer Furnished Item
CS Coordinate System
DRS Data Relay Satellite
ESA European Space Agency
ESTEC European Space Technology and Research Centre
GPL GNU Public License
GPS Global Positioning System
GS Ground Station
IERS International Earth Rotation Service
I/F Interface
LOS Line Of Sight
LUT Look-Up Table
OBT On-board Binary Time
OSF Orbit Scenario File
RAM Random Access Memory
SBT Satellite Binary Time
SRAR Satellite Relative Actual Reference
SSP Sub Satellite Point
SUM Software User Manual
S/W Software
TAI International Atomic Time
UTC Coordinated Universal Time
UT1 Universal Time UT1
WGS[84 World Geodetic System 1984


Nomenclature

CFI A group of CFI functions, and related software and documentation. that will be distributed by ESA to the users as an independent unit
CFI function A single function within a CFI that can be called by the user
Library A software library containing all the CFI functions included within a CFI plus the supporting functions used by those CFI functions (transparently to the user)

Notes in Terminology

In order to keep compatibility with legacy CFI libraries, the Earth Observation Mission CFI Software makes use of terms that are linked with missions already or soon in the operational phase like the Earth Explorers. This may be reflected in the rest of the document when examples of Mission CFI Software usage are proposed or description of Mission Files is given.


APPLICABLE AND REFERENCE DOCUMENTS

Applicable Documents

[GEN_SUM] Earth Observation Mission CFI Software. General Software User Manual. EO-MA-DMS-GS-019. Issue 4.27 07/06/24

Reference Documents

[MCD] Earth Observation Mission CFI Software. Conventions Document. EO-MA-DMS-GS-0001. Issue 4.27 07/06/24.
[MSC] Earth Observation Mission CFI Software. Mission Specific Customizations. EO-MA-DMS-GS-0018. Issue 4.27 07/06/24.
[EE_COMMON_SUM] Earth Observation Mission CFI Software. EECommon Software User Manual. EO-MA-DMS-GS-020. Issue 4.27 07/06/24.
[F_H_SUM] Earth Observation Mission CFI Software. FileHandling Software User Manual. EO-MA-DMS-GS-021. Issue 4.27 07/06/24.
[D_H_SUM] Earth Observation Mission CFI Software. DataHandling Software User Manual. EO-MA-DMS-GS-022. Issue 4.27 07/06/24.
[LIB_SUM] Earth Observation Mission CFI Software. Lib Software User Manual. EO-MA-DMS-GS-023 Issue 4.27 07/06/24.
[LOS_ALG] LOS Intersection. PE-TN-ESA-SY-0043

INTRODUCTION

Classes Overview

This software library contains the CFI classes with the methods required to perform accurate computation of pointing parameters from and to a satellite for various types of targets. It includes a set of methods to initialize the attitude of the platform and the instruments. The values provided by these methods are later used by all the other methods of the library.
The following CFI classes are included:

and the following auxiliary classes:

For furher information, please refer also to:

Attitude Data Flow

The following figure shows the tipical data flow for the attitude methods. First, the different transformations between the various reference frames are initialised. Then, given the spacecraft position, the attitude is calculated:

attitude_initialisation.jpg

Each different transformation can be initialised with different models:

sat_nom_init.jpg
sat_init.jpg
instr_init.jpg

Geolocation Routines Data Flow

The following figure shows the tipical data flow for the geolocation routines functions. First, the attitude should be calculated, and, if needed, the refraction and Digital Elevation Models initialised.

geolocation_routine_seq.jpg

The table below and the diagrams on the next pages describe the various Target.targetXXX methods.

Target.targetXXX method Description
Target.targetInter / Target.multiTargetInter It calculates the intersection point(s) of the line of sight defined by an elevation and an azimuth angle expressed in the input Attitude frame, with a surface(s) located at a certain geodetic altitude(s) over the Earth.
Target.targetTravelTime / Target.multiTargetTravelTime It calculates the point of the line or sight from the satellite (defined by an elevation and an azimuth angle expressed in the selected Attitude Frame) at a given travel time(s) along the (curved) line of sight.
Target.targetGroundRange It calculates the location of a point that is placed on a surface at a certain geodetic altitude over the Earth, that lays on the plane defined by theS/C position, the nadir and a reference point, and that is at a certain distance or ground range measured along that surface from that reference point. This reference point is calculated being the intersection of the previous surface with the line of sight defined by an elevation and azimuth angle in the input Attitude coordinate system.
Target.targetIncidenceAngle It calculates the location of a point that is placed on a surface at a certain geodetic altitude over the Earth and that is seen from the S/C on a line of sight that forms a certain azimuth angle in the input Attitude frame and that intersects that surface with a certain incidence angle.
Target.targetRange It calculates the location of a point that is placed on a surface at a certain geodetic altitude over the Earth, that is seen from the S/C on a line of sight that forms a certain azimuth angle in the input Attitude frame, and that is at a certain range or slant-range from the S/C.
Target.targetRangeRate It calculates the location of a point that is placed on a surface at a certain geodetic altitude over the Earth, that is at a certain range from S/C, and whose associated Earth-fixed target has a certain range-rate value.
Target.targetTangent It calculates the location of the tangent point over the Earth that is located on the line of sight defined by an elevation and azimuth angles expressed in the input Attitude frame.
Target.targetAltitude It calculates the location of the tangent point over the Earth that is located on a surface at a certain geodetic altitude over the Earth and that is on a line of sight that forms a certain azimuth angle in the input Attitude frame.
Target.targetStar It calculates the location of the tangent point over the Earth that is located on the line of sight that points to a star defined by its right ascension and declination coordinates.
Target.targetGeneric The cartesian state vector of the target is taken as an input.
Target.targetTangentSun It calculates the location of the tangent point over the Earth that is located on the line of sight that points to the Sun
Target.targetTangentMoon It calculates the location of the tangent point over the Earth that is located on the line of sight that points to the Moon
Target.targetStation It calculates the most relevant observation parameters of the link between the satellite and a ground station
Target.targetSc It calculates the most relevant observation parameters of the link between one source satellite and anothr target satellite.
pointing_1.jpg
pointing_2.jpg
pointing_3.jpg

As it can be seen from the list of functions, there are some functions that calculate several targets (Target.multiTargetXXX). The number of targets found by the functions is stored in the Target object. In addition to these "user" targets, two other categories of targets can be defined, "LOS" targets and "DEM" targets.

LOS targets

The idea is to get information about all the ray path points computed by a specific target routine along the Line of Sight (LOS) trajectory. For every target method, the Target parameter numLosTarget will store the number of points in the path. It applies when the variable "targetType" is equal to XPCFI_LOS_TARGET_TYPE.

  1. Start point of LOS. The spacecraft position (Instrument CS) shall be considered as the start point for the LOS path.
  2. Stop point of LOS. The stop point for the LOS path will be different depending on the selected target function; nominally it will be the resulting target point.

DEM targets

A DEM Target is defined as the intersection of a line of sight with the Earth Surface defined using a digital elevation model (DEM).
A DEM Target is calculated using as line of sight the LOS targets that has been computed previously with a target routine (Note that such LOS consist in a polygonal line, no necessarily a straight line). Consequently, to get a DEM target it is neccessary to follow these steps:

The digital elevation model of the Earth consists in a set of points defining a grid for which a measure of the altitude over the Earth reference elipsoid is given. The altitude of the points within each cell of the grid is computed by the CFI using a bilinear interpolation with the points of the corner of the cell. Details about the bilinear algorithm used to compute the intersection can be seen in [LOS_ALG].[LOS_ALG]

Light propagation model

When the light propagation model is enabled, the target functions keep into account the time spent by a generic signal travelling at the speed of light to:

Two distinct times are considered:

  1. The satellite time (T) is the time provided as input to the target function. It is:
    • in the TRANSMITTER mode: the time at which the satellite (instrument) emits the signal towards the target;
    • in the RECEIVER mode: the time at which the satellite (instrument) receives the signal emitted by the target.
  2. The target time is the satellite time T plus or minus the light travel time between satellite and target (dT). It is:
    • in the TRANSMITTER mode: T+dT, i.e. the target receives the signal sent by the sarellite with a delay dT;
    • in the RECEIVER mode: : T-dT, i.e. the satellite receives the signal emitted by the target with a delay dT.

dT is calculated as the light travel time from the satellite to target calculated with dT=0. When the light propagation model is not activated, it is assumed dT=0, therefore target and satellite are considered at the same time T.
According to the definitions above, the Line of Sight (LOS) can be defined as the segment joining satellite and target at their correspondent times.
For the following functions the calculation method is slightly different:

Target geometric properties (returned by the extra functions) are evaluated considering the two distinct times, for example:

Following figure shows an example using the Target.targetInter function.

light_propagation.jpg


The light propagation mode is set to RECEIVER and input azimuth,elevation are 0, 90 deg (assuming a local normal pointing). The signal is emitted by the target at time T-dT (blue point, let’s assume at geodetic co-ordinates (lon,lat,h) and EF co-ordinates (X,Y,Z) ) and is received by the satellite at time T (red triangle). Due to Earth rotation, at time T the observed target has moved to the red point.
Here are some examples of results from Target.extra… functions:

The same results are given by the Target.extra… functions if the Target.targetGeneric is called with input target at EF co-ordinates (X,Y,Z) and velocity set to zero.

To activate the light propagation mode the modelId object must be initialized as follow:

  1. for TRANSMITTER mode:


    long mode;
    vector<long> models;

    mode = XLCFI_MODEL_CONFIG;
    models.clear();
    ...
    models.push_back(XLCFI_MODEL_LIGHT_PROPAGATION_TRANSMITTER);
    modelId = new ModelId(mode, models);

  2. for RECEIVER mode:


    long mode;
    vector<long> models;

    mode = XLCFI_MODEL_CONFIG;
    models.clear();
    ...
    models.push_back(XLCFI_MODEL_LIGHT_PROPAGATION_RECEIVER);
    modelId = new ModelId(mode, models);


LIBRARY INSTALLATION

For a detailed description of the installation of any CFI library, please refer to [GEN_SUM].


LIBRARY USAGE

Compilation hints

Note that to use the POINTING software library, the following other CFI software libraries are required:

Third party libraries:

In order to improve run-time performance, some methods (e.g. Target.extraListVector, Target.extraListMain, Target.extraListAux, Target.extraListEfTarget, Target.extraListTargetToSun, Target.extraListTargetToMoon,Target.extraListSpecularReflection) perform their computations in multi-threading mode. The multi-threading code of the Pointing functions uses the OpenMP API (see http://en.wikipedia.org/wiki/OpenMP). OpenMP is not supported in the clang compiler, therefore such functions work in single-thread mode in MacOS.

To use the CFI ORBIT software library in an user application, that application must import the classes that are going to be used. To do this, it must be taken into account that all CFI classes are part of EECFI package. For instance, to import class OneCfiClass:

For Java to find the classes, the jar files where they are defined must be included in the CLASSPATH environment variable. For Pointing library, CLASSPATH must be something like:

where jar_directory is the directory where the jar files are stored.

CFI libraries call C++ native methods. These methods are defined in dynamic libraries, which name and extension depend on the operating system:

If these libraries are stored in cfi_lib_dir, this directory must be included in the path where the system looks for dynamic libraries (LD_LIBRARY_PATH in LINUX and SOLARIS, DYLD_LIBRARY_PATH in MAC systems, PATH in WINDOWS sytem).

Enumerations

Every CFI library has defined constant values that can be used as input for several methods of the classes. They are grouped in a class with the name EnumLibrary. To use them, a static import is recommended:

import static EECFI.EnumLibrary.*;

so the constants can be used directly, without prefixing with package name and class name.
You can consult the constants available for this library here.


ERROR HANDLING

The error management in Java POINTING is made throw exceptions, that is, if any error is produced, an exception of type CfiError is thrown and it must be catched putting the code inside a try-catch block.
See [GEN_SUM] to know more about how to handle the CFI errors. For a descripton about the CfiError class and its methods, see [EE_COMMON_SUM].


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