Introduction

textkernel is a set of routines for parsing SPICE text kernels. This module implements the complete syntax specification as discussed in the SPICE Kernel Required Reading document, "kernel.req": https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/req/kernel.html

textkernel is a product of the PDS Ring-Moon Systems Node.

Installation

The textkernel module is available via the rms-textkernel package on PyPI and can be installed with:

pip install rms-textkernel

Getting Started

The textkernel module provides two functions for reading text kernels:

• from_text: Given a string representing the contents of a text kernel, return a dictionary of the values found.
• from_file: Given the path to a text kernel, read the contents and return a dictionary of the values found.

and two functions for manipulating text kernels:

• continued_value: Interpret a list of strings as one or more continued strings.
• update_dict: Merge the contents of two text kernel dictionaries, preserving nested values.

Details of each function are available in the module documentation.

The simplest use case is as follows:

import textkernel
tkdict = textkernel.from_file('path/to/kernel/file')

(The file path can be any URL accepted by FCPath.)

The returned dictionary tkdict is keyed by all the parameter names (on the left side of an equal sign) in the text kernel, and each associated dictionary value is that found on the right side. Values are Python ints, floats, strings, datetime objects, or lists of one or more of these.

Hierarchical Keys

For convenience, the returned dictionary adds additional "hierarchical" keys that provide alternative access to the same values. Hierarchical keys are substrings from the original parameter name, which return a sub-dictionary keyed by part or all of the remainder of that parameter name.

Parameter names with a slash are split apart as if they represented components of a file directory tree, so these are equivalent:

tkdict["DELTET/EB"] == tkdict["DELTET"]["EB"]

When a body or frame ID is embedded inside a parameter name, it is extracted, converted to integer, and used as a piece of the hierarchy, making these equivalent:

tkdict["BODY399_POLE_RA"] == tkdict["BODY"][399]["POLE_RA"]
tkdict["SCLK01_MODULI_32"] == tkdict["SCLK"][-32]["01_MODULI"]

Leading and trailing underscores before and after the embedded numeric ID are stripped from the hierarchical keys, as you can see in the examples above. Note also that the components of the parameter name are re-ordered in the second example, so that the second key is always the numeric ID.

When the name associated with a body or frame ID is known, that name can be used in the place of the integer ID:

tkdict["BODY"][399] == tkdict["BODY"]["EARTH"]
tkdict["FRAME"][10013] == tkdict["FRAME"]["IAU_EARTH"]
tkdict["SCLK"][-32] == tkdict["SCLK"]["VOYAGER 2"]

If a frame is uniquely or primarily associated with a particular central body, that body's ID can also be used in place of the frame's ID:

tkdict["FRAME"][399] == tkdict["FRAME"]["IAU_EARTH"]

Note that the "BODY" and "FRAME" dictionaries also have an additional entry keyed by "ID", which returns the associated integer ID:

tkdict["FRAME"][623]["ID"] = 623
tkdict["FRAME"]["IAU_SUTTUNGR"]["ID"] = 623

This ensures that you can look up a body or frame by name and readily obtain its ID.

Contributing

Information on contributing to this package can be found in the Contributing Guide.

Links

• Documentation
• Repository
• Issue tracker
• PyPi

Licensing

This code is licensed under the Apache License v2.0.