Process BSP

Process BSP#

Utilities for extracting data from a JPL DE ephemeris file.

The processing of the .bsp file partially relies on, then is heavily influenced by, the implementation in the jplephem package.

jorbit.ephemeris.process_bsp.extract_data(center, target, ephem_file, earliest_time, latest_time)[source]#

Extracts the Chebyshev coefficients for a given target and center from an SPK file.

Note: assumes that there is only one segment for each target/center pair in the SPK file. This is valid for planetary ephemerides like DE440, but not necessarily for other .bsp files like those generated for specific asteroids, which may have multiple segments for the same target/center pair.

Parameters:

  • center (str) – The center ID of an ephemeris segment.

  • target (str) – The target ID of an ephemeris segment.

  • ephem_file (str) – The path to the SPK file. Uses astropy’s download_file function to download and cache the file if it isn’t present in the cache.

  • earliest_time (Time) – The start time for our region of interest. Smaller time windows will result in smaller in-memory ephemeris objects.

  • latest_time (Time) – The latest time for the ephemeris.

Returns:

A tuple containing the Chebyshev coefficients for the given target and center. More specifically, the tuple contains (init, intlen, coeff), where init is the initial time of the segment, intlen is the interval length, and coeff is the Chebyshev coefficients.

Return type:

tuple

jorbit.ephemeris.process_bsp.merge_data(inits, intlens, coeffs, earliest_time, latest_time)[source]#

Merges data for multiple targets into a single set of coefficients.

This takes all of the data extracted from individual target/center segments and merges them into larger jnp.ndarrays. All objects will now use the same number of coefficients to describe each interval, so objects that were previously missing high-order coefficients will have those zero padded. Also, all objects will now have the same number of intervals (but those intervals will have distinct inits), so objects that were previously missing intervals will have those also zero padded.

Parameters:

  • inits (list) – A list of initial times for each target.

  • intlens (list) – A list of interval lengths for each target.

  • coeffs (list) – A list of Chebyshev coefficients for each target.

  • earliest_time (Time) – The earliest time to consider.

  • latest_time (Time) – The latest time to consider.

Returns:

A tuple containing the merged initial time, interval length, and coefficients.

Return type:

tuple