readBinDAF: Read a generic binary DAF file

In Rafael-Ayala/asteRisk: Computation of Satellite Position

Read a generic binary DAF file

Description

DAF (Double Precision Array File) is a binary file architecture designed to store arrays of double precision arrays used by SPICE, NAIF toolkit software library. The architecture forms the basis of multiple file formats used to store different data related to astrodynamics, such as SPK, PCK and CK files (https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/daf.html).

DAF files provide a generic architecture onto which more specific file formats are implemented. They are organized in records of fixed length (1024 bytes) containing different information. The first record is called the file record, and contains global metadata for the file. This is followed by an optional block comprising any number of comment records. After this, the file consits of sets of summary records, name records and element records. These are structured as blocks of 1 summary record (which contains multiple array summaries, providing metadata about each array), followed by 1 name record (comprising names for the corresponding arrays whose summaries were in the previous summary record) and finally by as many element records as required to store the arrays described in the corresponding summary records. For a detailed description of the DAF architecture, see NAIF documentation (https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/daf.html).

This function allows to read any binary file with a DAF architecture in a generic way, without applying any specific formatting to its contents. Note that this will result in just a list of the file global metadata, comments and different arrays (each one with a summary, a name and a set of elements). The number of elements and meaning of each included in each array, as well as the descriptor integers and doubles contained in the summaries, vary for each specific file type. Therefore, reading a DAF file generically is not likely to bring much meaningful information, unless a precise understanding of the specific file format is taken into account later.

Usage

readBinDAF(filename)

Arguments

filename

Path to the binary DAF file.

Value

A list with three elements. The first element, named metadata, corresponds to the "file record", which is always the first record in a DAF file, and is a list with the following metadata elements:

fileType	String of the format DAF/XXXX indicating the specific file format for the DAF file
numDoublesSummary	Number of double precision numbers in each array summary
numIntsSummary	Number of integers in each array summary
summaryRecordSizeDoubles	Size of each array summary in doubles
numCharsName	Number of characters in each array name
description	String with an internal name or description of the DAF file
firstSummaryRecNum	Integer indicating which is the 1st summary record This can be used to infer the number of comment files. For example, a value of 3 indicates that the 3rd record is the 1st summary record. Since the 1st record is always the file record, this means there is 1 comment record
lastSummaryRecNum	Integer indicating which is the last summary record
firstFreeAddress	Integer indicating the first free address (in bytes) of the file, i.e., the address of the last byte of the last element record plus 1
endianString	String indicating the endianness of the file. This is automatically taken into account when reading the file. It can be either LTL-IEEE (little endianness) or BIG-IEEE (big endianness), and is determined by the architecture of the system where the file was written
ftpString	String used to verify integrity of the DAF file. It should be exactly equal to "FTPSTR:\r:\n:\r\n:\r:\x81:\020\xce:ENDFTP"

The second element is named comments, and is a character vector where each element is a line of comments.

The third element is named arrays, and is a nested list where each top-level element represents one of the arrays stored in the DAF file and its associated metadata. Each of the top-level elements is itself a list with the following 3 elements:

arrayName	String with the name of the array
arraySummary	A list with the multiple doubles and integers that are stored in each array summary of summary records and which provide metadata describing each array. The elements are named as Double1, Double2, ..., DoubleN; Integer1, Integer2, ..., Integer(M-2) and finally initialArrayAddress and finalArrayAddress. N and M are respectively the number of doubles and integers in each array summary, and are given in elements numDoublesSummary and numIntsSummary of the metadata element of the top-level list. Note that the number of doubles and integers describing each array, as well as the meaning of each, varies between different specific file formats, and therefore no exact meaning can be derived when simply reading the file as a generic DAF file. The exception to this are the last 2 integers, which always are respectively the initial and final addresses of the elements corresponding to the array within the DAF file, in double precision numbers (and therefore, in order to obtain byte addresses it must be multiplied by 8 and subtract 7)
arrayElements	A numeric vector with all the elements of the array. Note that this includes potentially constants, actual data and additional array metadata. Furthermore, the number, order and meaning of the elements differs greatly between different specific types and subtypes of DAF files, and therefore it is hard to extract any meaningful information without knowledge of the internal organization of each array

References

https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/daf.html

Examples

# The file vgr2_jup230.bsp provided with the package includes information for the
# Jupiter flyby of Voyager 2

testDAF <- readBinDAF(paste0(path.package("asteRisk"), "/vgr2_jup230.bsp"))
testDAF$metadata
# The file seems to be of type SPK
testDAF$comments
length(testDAF$arrays)
# It contains a single array

Rafael-Ayala/asteRisk documentation built on May 16, 2024, 5:24 p.m.