Package org.orekit.files.ccsds

Class StreamingOemWriter

java.lang.Object

org.orekit.files.ccsds.StreamingOemWriter

public class StreamingOemWriter
extends Object

A writer for OEM files.

Each instance corresponds to a single OEM file. A new OEM ephemeris segment is started by calling newSegment(Frame, Map).

Metadata

The OEM metadata used by this writer is described in the following table. Many metadata items are optional or have default values so they do not need to be specified. At a minimum the user must supply those values that are required and for which no default exits: Keyword.OBJECT_NAME, and Keyword.OBJECT_ID. The usage column in the table indicates where the metadata item is used, either in the OEM header or in the metadata section at the start of an OEM ephemeris segment.

The OEM metadata for the whole OEM file is set in the constructor. Any of the metadata may be overridden for a particular segment using the metadata argument to newSegment(Frame, Map).

Keyword	Usage	Obligatory	Default	Reference
Keyword.CCSDS_OEM_VERS	Header	Yes	CCSDS_OEM_VERS	Table 5-2
Keyword.COMMENT	Header	No		Table 5-2
Keyword.CREATION_DATE	Header	Yes	Now	Table 5.2, 6.5.9
Keyword.ORIGINATOR	Header	Yes	DEFAULT_ORIGINATOR	Table 5-2
Keyword.OBJECT_NAME	Segment	Yes		Table 5-3
Keyword.OBJECT_ID	Segment	Yes		Table 5-3
Keyword.CENTER_NAME	Segment	Yes	Guessed from the segment's frame	Table 5-3
Keyword.REF_FRAME	Segment	Yes	Guessed from the segment's frame	Table 5-3, Annex A
Keyword.REF_FRAME_EPOCH	Segment	No		Table 5-3, 6.5.9
Keyword.TIME_SYSTEM	Segment	Yes	Guessed from timeScale set in the constructor.	Table 5-3, Annex A
Keyword.START_TIME	Segment	Yes	Date of initial state in Segment.init(...)	Table 5-3, 6.5.9
Keyword.USEABLE_START_TIME	Segment	No		Table 5-3, 6.5.9
Keyword.STOP_TIME	Segment	Yes	Target date in Segment.init(...)	Table 5-3, 6.5.9
Keyword.USEABLE_STOP_TIME	Segment	No		Table 5-3, 6.5.9
Keyword.INTERPOLATION	Segment	No		Table 5-3
Keyword.INTERPOLATION_DEGREE	Segment	No		Table 5-3

The Keyword.TIME_SYSTEM must be constant for the whole file and is used to interpret all dates except Keyword.CREATION_DATE. The guessing algorithm is not guaranteed to work so it is recommended to provide values for Keyword.CENTER_NAME, Keyword.REF_FRAME, and Keyword.TIME_SYSTEM to avoid any bugs associated with incorrect guesses.

Standardized values for Keyword.TIME_SYSTEM are GMST, GPS, ME, MRT, SCLK, TAI, TCB, TDB, TCG, TT, UT1, and UTC. Standardized values for Keyword.REF_FRAME are EME2000, GCRF, GRC, ICRF, ITRF2000, ITRF-93, ITRF-97, MCI, TDR, TEME, and TOD. Additionally ITRF followed by a four digit year may be used.

Examples

This class can be used as a step handler for a Propagator, or on its own. Either way the object name and ID must be specified. The following example shows its use as a step handler.

 Propagator propagator = ...; // pre-configured propagator
 Appendable out = ...; // set-up output stream
 Map<Keyword, String> metadata = new LinkedHashMap<>();
 metadata.put(Keyword.OBJECT_NAME, "Vanguard");
 metadata.put(Keyword.OBJECT_ID, "1958-002B");
 StreamingOemWriter writer = new StreamingOemWriter(out, utc, metadata);
 writer.writeHeader();
 Segment segment = writer.newSegment(frame, Collections.emptyMap());
 propagator.setMasterMode(step, segment);
 propagator.propagate(startDate, stopDate);
 

Alternatively a collection of state vectors can be written without the use of a Propagator. In this case the Keyword.START_TIME and Keyword.STOP_TIME need to be specified as part of the metadata.

 List<TimeStampedPVCoordinates> states = ...; // pre-generated states
 Appendable out = ...; // set-up output stream
 Map<Keyword, String> metadata = new LinkedHashMap<>();
 metadata.put(Keyword.OBJECT_NAME, "Vanguard");
 metadata.put(Keyword.OBJECT_ID, "1958-002B");
 StreamingOemWriter writer = new StreamingOemWriter(out, utc, metadata);
 writer.writeHeader();
 // manually set start and stop times for this segment
 Map<Keyword, String> segmentData = new LinkedHashMap<>();
 segmentData.put(Keyword.START_TIME, start.toString());
 segmentData.put(Keyword.STOP_TIME, stop.toString());
 Segment segment = writer.newSegment(frame, segmentData);
 segment.writeMetadata(); // output metadata block
 for (TimeStampedPVCoordinates state : states) {
     segment.writeEphemerisLine(state);
 }
 

Author:

Evan Ward

See Also:

CCSDS 502.0-B-2 Orbit Data Messages, CCSDS 500.0-G-3 Navigation Data Definitions and Conventions, OEMWriter

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
class	StreamingOemWriter.Segment	A writer for a segment of an OEM.

Field Summary

Fields

Modifier and Type	Field	Description
static String	CCSDS_OEM_VERS	Version number implemented.
static String	DEFAULT_ORIGINATOR	Default value for Keyword.ORIGINATOR.

Constructor Summary

Constructors

Constructor	Description
StreamingOemWriter(Appendable writer, TimeScale timeScale, Map<Keyword,String> metadata)	Create an OEM writer than streams data to the given output stream.

Method Summary

Modifier and Type	Method	Description
StreamingOemWriter.Segment	newSegment(Frame frame, Map<Keyword,String> segmentMetadata)	Create a writer for a new OEM ephemeris segment.
void	writeHeader()	Writes the standard OEM header for the file.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

CCSDS_OEM_VERS

public static final String CCSDS_OEM_VERS

Version number implemented.

See Also:

Constant Field Values

DEFAULT_ORIGINATOR

public static final String DEFAULT_ORIGINATOR

Default value for Keyword.ORIGINATOR.

See Also:

Constant Field Values

Constructor Detail

StreamingOemWriter

public StreamingOemWriter(Appendable writer,
                          TimeScale timeScale,
                          Map<Keyword,String> metadata)
                   throws OrekitException

Create an OEM writer than streams data to the given output stream.

Parameters:

writer - The output stream for the OEM file. Most methods will append data to this writer.

timeScale - for all times in the OEM except Keyword.CREATION_DATE. See Section 5.2.4.5 and Annex A.

metadata - for the satellite. Can be overridden in newSegment(Frame, Map) for a specific segment. See StreamingOemWriter.

Throws:

OrekitException - If the UTC time scale could not be used.

Method Detail

writeHeader

public void writeHeader()
                 throws IOException

Writes the standard OEM header for the file.

Throws:

IOException - if the stream cannot write to stream

newSegment

public StreamingOemWriter.Segment newSegment(Frame frame,
                                             Map<Keyword,String> segmentMetadata)

Create a writer for a new OEM ephemeris segment.

The returned writer can only write a single ephemeris segment in an OEM. This method must be called to create a writer for each ephemeris segment.

Parameters:

frame - the reference frame to use for the segment. If this value is null then StreamingOemWriter.Segment.handleStep(SpacecraftState, boolean) will throw a NullPointerException and the metadata item Keyword.REF_FRAME must be specified in the metadata.

segmentMetadata - the metadata to use for the segment. Overrides for this segment any other source of meta data values. See StreamingOemWriter(java.lang.Appendable, org.orekit.time.TimeScale, java.util.Map<org.orekit.files.ccsds.Keyword, java.lang.String>) for a description of which metadata are required and how they are determined.

Returns:

a new OEM segment, ready for writing.