Changelog

SuperNOVAS C/C++ astrometry library

All notable changes to the SuperNOVAS library will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Semantic Versioning.

[Unreleased]

Release candidate for the next feature release, expected around 1 February 2025.

Fixed

Fixes to GCC version checking for macros.

Added

#57: New generic redshift-handling functions novas_v2z(), novas_z2v().
#57, #102: New make_redshifted_cat_entry() and make_redshifted_object() to simplify the creation of distant catalog sources that are characterized with a redshift measure rather than a radial velocity value.
#58: New functions to calculate and apply additional gravitational redshift corrections for light that originates near massive gravitating bodies (other than major planets, or Sun or Moon), or for observers located near massive gravitating bodies (other than the Sun and Earth). The added functions are grav_redshift(), redhift_vrad(), unredshift_vrad(), novas_z_add(), and novas_z_inv().
#83: CALCEPH integration: novas_use_calceph() and/or novas_use_calceph_planets() to specify and use ephemeris data via CALCEPH for Solar-system sources in general, and for major planets specifically; and novas_calceph_use_ids() to specify whether object.number in NOVAS_EPHEM_OBJECT type objects is a NAIF ID (default) or else a CALCEPH ID number of the Solar-system body. These functions are provided by the libsolsys-calceph.so[.1] and/or .a plugin libraries, which are built contingent on the CALCEPH_SUPPORT variable being set to 1 prior to the build. The build of the plugin module requires an accessible installation of the CALCEPH development files (C headers and unversioned static or shared libraries depending on the needs of the build).
#86: NAIF CSPICE integration: novas_use_cspice(), novas_use_cspice_planets(), novas_use_cspice_ephem() to use the NAIF CSPICE library for all Solar-system sources, major planets only, or for other bodies only. NOVAS_EPHEM_OBJECTS should use NAIF IDs with CSPICE (or else -1 for name-based lookup). Also provides cspice_add_kernel() and cspice_remove_kernel() functions for convenience to manage the set of active kernels (#89). These functions are provided by the libsolsys-cspice.so[.1] and/or .a plugin libraries, which are built contingent on the CSPICE_SUPPORT variable being set to 1 prior to the build. The build of the plugin module requires an accessible installation of the CSPICE development files (C headers and unversioned static or shared libraries depending on the needs of the build).
#87: Added novas_planet_for_name() function to return the NOVAS planet ID for a given (case insensitive) name.
NOVAS-NAIF conversions for major planets (and Sun, Moon, SSB): novas_to_naif_planet() (planet centers), novas_to_dexxx_planet() (mixed planet center/barycenter for DExxx ephemeris files), and the inverse naif_to_novas_planet().
Added get_planet_provider() and get_planet_provider_hp() functions for convenience to return the solarsystem() / solarsystem_hp() type custom planet ephemeris provider functions currently configured, so they may be used directly, outside of ephemeris() calls.
#93: Now supporting make install with prefix and DESTDIR support (e.g. make prefix="/opt" install to install under /opt, and/or make DESTDIR="/tmp/stage" install to stage install under /tmp/stage). You can also set other standard directory variables, as prescribed by the GNU standard to further customize the install locations.
#95, #98: Added support for using orbital elements. object.type can now be set to NOVAS_ORBITAL_OBJECT, whose orbit can be defined by the set of novas_orbital, relative to a novas_orbital_system. You can initialize an object with a set of orbital elements using make_orbital_object(), and for planetary satellite orbits you might use novas_set_orbsys_pole(). For orbital objects, ephemeris() will call on the new novas_orbit_posvel() to calculate positions. While orbital elements do not always yield precise positions, they can for shorter periods, provided that the orbital elements are up-to-date. For example, the Minor Planer Center (MPC) publishes accurate orbital elements for all known asteroids and comets regularly. For newly discovered objects, this may be the only and/or most accurate information available anywhere.
#97: Added NOVAS_EMB (Earth-Moon Barycenter) and NOVAS_PLUTO_BARYCENTER to enum novas_planets to distinguish from the planet center in calculations.
#98: Added gcrs_to_tod() / tod_to_gcrs() and gcrs_to_mod() / mod_to_gcrs() vector conversion functions for convenience.
Added various object initializer macros in novas.h for the major planets, Sun, Moon, and barycenters, e.g. NOVAS_EARTH_INIT or NOVAS_SSB_INIT. These wrap the parametric NOVAS_PLANET_INIT(num, name) macro, and can be used to simplify the initialization of NOVAS objects.
Added more physical unit constants to novas.h and a corresponding section in the README on how these may be used to convert to/from NOVAS conventional quantities.
SuperNOVAS headers now include each other as system-headers, not local headers. This is unlikely to affect anything really but it is more proper for an installation of the library, and works with our own Makefile too.
Added ‘Coordinate Systems and Conversions’ flowchart to README.
Added a GNU standard documentation targets to Makefile.
Added infer make target for running Facebook’s infer static analysis tool.
Added missing error tracing in nutation().
Added README.md Figure 1, to clarify relation of coordinate systems and (Super)NOVAS function to convert vectors among them.

Changed

#96: Changed object structure to include novas_orbital for NOVAS_ORBITAL_OBJECT types. To keep ABI compatibility to earlier SuperNOVAS releases, make_object() will not initialize the new .orbit field unless type is set to NOVAS_ORBITAL_OBJECT (which was not available before).
#97: Updated NOVAS_PLANETS, NOVAS_PLANET_NAMES_INIT, and NOVAS_RMASS_INIT macros to include the added planet constants.
make check now runs both static analysis by cppcheck (new analysis target) and regression tests (test target), in closer conformance to GNU Makefile standards.
Added -g to default CFLAGS as a matter of GNU best practice.
Various small tweaks to Makefiles.
Updated README.md documentation.

[1.1.1] - 2024-10-28

Bug fix release. Nothing too scary, mainly just a collection of smaller fixes and improvements.

Fixed

#55: Relativistic corrections to radial velocity were still not applied correctly. The revised calculation now uses the actual relativistic velocity differential between the source and observer to apply the appropriate time dilation factor, and applies gravitational corrections for Sun and Earth consistently at source and observer alike.
#64: NOVAS_TAI_TO_TT definition had wrong decimal in last place, thus was 3 ms off from what it should have been. (thanks to kiranshila)
#68: readeph_dummy() dummy implementation in readeph0.c called non existing error handler function.

Changed

#59: For observing major planets (and Sun and Moon) rad_vel(), rad_vel2(), place(), and novas_sky_pos() will include gravitational corrections to radial velocity for light originating at the surface, and observed near Earth or else at a large distance away. These corrections, along with those for the Solar potential at the source, may be skipped for rad_vel() / rad_vel2() by setting d_src_sun negative.
#55: Use relativistic formulae to add/difference velocities (i.e. change velocity reference frame).
#60: Moved SuperNOVAS-only functions to a separate super.c module to alleviate the bloating of novas.c, which can still be used as a self-contained, standalone, NOVAS C replacement for legacy applications if need be.
#62: Improve debug mode error tracing when NAN values are returned, so the trace indicates NAN rather than a bogus integer return value before.
#66: Various tweaks for C/C++ best practices (by kiranshila)
#67: Use accuracy argument in tod_to_cirs(). (thanks to kiranshila)
#68: Various improvements to debug error tracing.
#73: Initializer macros (primarily for internal use), forced ‘use’ of unused variables after declarations, and no order-only-dependencies in Makefiles – in order to cure warnings and to conform with older compilers and make.
Slight tweaks to Makefile, and .mk snippets, with added make configurability.

[1.1.0] - 2024-08-04

Feature release. Introducing a more efficient and elegant approach to position and velocity calculations using observer frames; versatile handling of astronomical timescales; and support for further observer locations, coordinate reference systems, and atmospheric refraction models. The release also fixes a number of bugs, of varying severity, which affected prior SuperNOVAS releases.

Fixed

#29: Fix portability to non-Intel platforms. Previously, SuperNOVAS used char for storing small integer coefficients, assuming char was signed. However, on some platforms like ARM and PowerPC char is unsigned, which broke calculations badly. As of now, we use the explicit platform independent signed int8_t storage type for these coefficients.
#38: gcrs_to_j2000() transformed in the wrong direction in v1.0.
#39: tod_to_itrs() used wrong Earth rotation measure (NOVAS_ERA instead of NOVAS_GST) in v1.0.
#45: cel2ter() invalid output in v1.0 with CIRS input coordinates (erot = EROT_ERA and class = NOVAS_DYNAMICAL_CLASS) if output vector was distinct from input vector. Affects cirs_to_itrs() also.
#36: tt2tdb() Had a wrong scaling in sinusoidal period in v1.0, resulting in an error of up to +/- 1.7 ms.
#37: gcrs_to_cirs() did not handle well if input and output vectors were the same in v1.0.
#28: Division by zero bug in d_light() (since NOVAS C 3.1) if the first position argument is the ephemeris reference position (e.g. the Sun for solsys3.c). The bug affects for example grav_def(), where it effectively results in the gravitational deflection due to the Sun being skipped. See Issue #28.
#41: grav_def() gravitating body position antedated somewhat incorrectly (in v1.0) when observed source is a Solar-system object between the observer and the gravitating body. The resulting positional error is typically small at below 10 uas.
#50: The NOVAS C 3.1 implementation of rad_vel() applied relativistic corrections for a moving observer conditional on applying relativistic gravitational corrections (for Sun and/or Earth potential) for the observer. However, it seems more reasonable that the corrections for a moving observer should be applied always and independently of the (optional) gravitational corrections.
#34: place() radial velocities were not quite correct in prior SuperNOVAS releases. The radial velocity calculation now precedes aberration, since the radial velocity that is observed is in the geometric direction towards the source (unaffected by aberration). As for gravitational deflection, the geometric direction is the correct direction in which light was emitted from the source for sidereal objects. For Solar system sources we now reverse trace the deflected light to calculate the direction in which it was emitted from the source. As such, the radial velocities calculated should now be precise under all conditions. The typical errors of the old calculations were up to tens of m/s because of aberration, and a few m/s due to the wrong gravitational deflection calculation.
#24: Bungled definition of SUPERNOVAS_VERSION_STRING in novas.h in v1.0.
Bungled definition of NOVAS_OBSERVER_PLACES in novas.h in v1.0.

Added

#33: New observing-frame based approach for calculations (frames.c). A novas_frame object uniquely defines both the place and time of observation, with a set of pre-calculated transformations and constants. Once the frame is defined it can be used very efficiently to calculate positions for multiple celestial objects with minimum additional computational cost. The frames API is also more elegant and more versatile than the low-level NOVAS C approach for performing the same kind of calculations. And, frames are inherently thread-safe since post-creation their internal state is never modified during the calculations. The following new functions were added: novas_make_frame(), novas_change_observer(), novas_geom_posvel(), novas_geom_to_app(), novas_sky_pos(), novas_app_to_hor(), novas_app_to_geom(), novas_hor_to_app().
#33: New coordinate system transformations via the novas_transform structure. You may use these transforms to express position / velocity vectors, calculated for a given observer and time, in the coordinate reference system of choice.The following new functions were added: novas_make_transform(), novas_invert_transform(), novas_transform_vector(), and novas_transform_sky_pos().
#33: New novas_timespec structure for the self-contained definition of precise astronomical time (timescale.c). You can set the time via novas_set_time() or novas_set_split_time() to a JD date in the timescale of choice (UTC, UT1, GPS, TAI, TT, TCG, TDB, or TCB), or to a UNIX time with novas_set_unix_time(). Once set, you can obtain an expression of that time in any timescale of choice via novas_get_time(), novas_get_split_time() or novas_get_unix_time(). And, you can create a new time specification by incrementing an existing one, using novas_increment_time(), or measure time differences via novas_diff_time(), novas_diff_tcg(), or novas_diff_tcb().
Added novas_planet_bundle structure to handle planet positions and velocities more elegantly (e.g. for gravitational deflection calculations).
#32: Added grav_undef() to undo gravitational bending of the observed light to obtain geometric positions from observed ones.
Added obs_posvel() to calculate the observer position and velocity relative to the Solar System Barycenter (SSB).
Added obs_planets() to calculate apparent planet positions (relative to observer) and velocities (w.r.t. SSB).
Added new observer locations NOVAS_AIRBORNE_OBSERVER for an observer moving relative to the surface of Earth e.g. in an aircraft or balloon based telescope platform, and NOVAS_SOLAR_SYSTEM_OBSERVER for spacecraft orbiting the Sun. Both of these use the observer.near_earth strcture to define (positions and) velocities as appropriate. Hence the 'near_earth name is a bit misleading, but remains for back compatibility.
Added coordinate reference systems NOVAS_MOD (Mean of Date) which includes precession by not nutation and NOVAS_J2000 for the J2000 dynamical reference system.
New observer locations NOVAS_AIRBORNE_OBSERVER and NOVAS_SOLAR_SYSTEM_OBSERVER, and corresponding make_airborne_observer() and make_solar_system_observer() functions. Airborne observers have an Earth-fixed momentary location, defined by longitude, latitude, and altitude, the same way as for a stationary observer on Earth, but are moving relative to the surface, such as in an aircraft or balloon based observatory. Solar-system observers are similar to observers in Earth-orbit but their momentary position and velocity is defined relative to the Solar System Barycenter (SSB), instead of the geocenter.
Added humidity field to on_surface structure, e.g. for refraction calculations at radio wavelengths. The make_on_surface() function will set humidity to 0.0, but the user can set the field appropriately afterwards.
New set of built-in refraction models to use with the frame-based novas_app_to_hor() / novas_hor_to_app() functions. The models novas_standard_refraction() and novas_optical_refraction() implement the same refraction model as refract() in NOVAS C 3.1, with NOVAS_STANDARD_ATMOSPHERE and NOVAS_WEATHER_AT_LOCATION respectively, including the reversed direction provided by refract_astro(). The user may supply their own custom refraction also, and may make use of the generic reversal function novas_inv_refract() to calculate refraction in the reverse direction (observer vs astrometric elevations) as needed.
Added radio refraction model novas_radio_refraction() based on the formulae by Berman & Rockwell 1976.
Added cirs_to_tod() and tod_to_cirs() functions for efficient tranformation between True of Date (TOD) and Celestial Intermediate Reference System (CIRS), and vice versa.
Added make_cat_object() function to create a NOVAS celestial object structure from existing cat_entry data.
Added rad_vel2() to calculate radial velocities precisely in the presense of gravitational deflection i.e., when the direction in which light was emitted is different from the direction it is detected by the observer. This new function is now used by both place() and novas_sky_pos().
make help to provide a brief list and explanation of the available build targets. (Thanks to @teuben for suggesting this.)
Added GitHub CI regression testing for non-x86 platforms: armv7, aarch64, riscv64, ppc64le. Thus, we should avoid misphaps, like the platform specific bug Issue #29, in the future.

Changed

#42: cio_array() can now parse the original ASCII CIO locator data file (data/CIO_RA.TXT) efficiently also, thus no longer requiring a platform-specific binary translation via the cio_file tool.
#51: The NOVAS C implementation of rad_vel() has ignored this redshifting when the Sun was being observed. From now on, we shall gravitationally reference radial velocities when observing the Sun to its photosphere.
cio_file tool parses interval from header rather than the less precise differencing of the first two record timestamps. This leads to cio_array() being more accurately centered on matching date entries, e.g. J2000.
grav_def() estimation of light time to where light passes nearest to gravitating body is improved by starting with the body position already antedated for light-time for the gravitating mass. The change typically improves the grativational deflection calculations at the few uas level.
grav_def() is simplified. It no longer uses the location type argument. Instead it will skip deflections due to any body, if the observer is within ~1500 km of its center.
place() now returns an error 3 if and only if the observer is at (or very close, to within ~1.5m) of the observed Solar-system object.
Improved precision of some calculations, like era(), fund_args(), and planet_lon() by being more careful about the order in which terms are accumulated and combined, resulting in a small improvement on the few uas (micro-arcsecond) level.
vector2radec(): ra or dec arguments may now be NULL if not required.
tt2tdb() Now uses the same, slightly more precise series as the original NOVAS C tdb2tt().
rad_vel() You can use negative values for the distances to skip particular gravitational corrections to the radial velocity measure. The value 0.0 also continues to have the same effect as before, except if the observed source is the Sun. Then d_src_sun being 0.0 takes on a different meaning than before: rather than skipping gravitational redshift corrections for the Solar potential (as before) we will apply gravitational corrections for light originating at the Sun’s photosphere.
PSI_COR and EPS_COR made globally visible again, thus improving NOVAS C 3.1 compatibility.
Convergent inverse calculations now use the novas_inv_max_iter variable declared in novas.c to specify the maximum number of iterations before inverse functions return with an error (with errno set to ECANCELED). Users may adjust this limit, if they prefer some other maximum value.
Adjusted regression testing to treat nan and -nan effectively the same. They both represent an equally invalid result regardless of the sign.
The default make target is now distro. It’s similar to the deprecated api target from before except that it skips building static libraries and cio_ra.bin.
make now generates .so shared libraries with SONAME set to lib<name>.so.1 where the .1 indicates that it is major version 1 of the ABI. All 1.x.x releases are expected to be ABI compatible with earlier releases.
lib/*.so files are now just symlinks to the actual versioned libraries lib/*.so.1. This conforms more closely to what Linux distros expect.
Default make skips local-dox target unless doxygen is available (either in the default PATH or else specified via the DOXYGEN variable, e.g. in config.mk). This way the default build does not have unexpected dependencies. (see Issue #22, thanks to @teuben).
make can be configured without editing config.mk simply by setting the appropriate shell variables (the same ones as in config.mk) prior to invoking make. Standard CC, CPPFLAGS, CFLAGS and LDFLAGS will also be used if defined externally.
make shared now also builds lib/libsolsys1.so.1 and lib/libsolsys2.so.1 shared libraries that can be used by programs that need solsys1 (via eph_manager) or solsys2 (via jplint) functionality.
make solsys now generates only the solarsystem() implementation objects that are external (not built in).
Eliminate unchecked return value compiler warnings from cio_file (used typically at build time only to generate cio_ra.bin).
jplint.f is moved to examples/ since it provides only a default implementation that typically needs to be tweaked for the particualr JPL PLEPH library one intends to use.
Doxygen tag file renamed to supernovas.tag for consistency.
Initialize test variables for reproducibility

[1.0.1] - 2024-05-13

Bug fix release with minor changes.

Fixed

cirs_to_itrs(), itrs_to_cirs(), tod_to_itrs(), and itrs_to_tod() all had a unit conversion bug in using the ut1_to_tt argument [s] when converting TT-based Julian date to UT1-based JD [day] internally. (thanks to hannorein)
Fixed errors in example.c [by hannorein].

Added

Added cirs_to_app_ra() and app_to_cirs_ra() for convenience to convert between right ascensions measured from the CIO (for CIRS) vs measured from the true equinox of date, on the same true equator of date.

Changed

Changed definition of NOVAS_AU to the IAU definition of exactly 1.495978707e+11 m. The old definition is also available as DE405_AU. (thanks to hannorein)
Various corrections and changes to documentation.

[1.0.0] - 2024-03-01

This is the initial release of the SuperNOVAS library. Changes are indicated w.r.t. the upstream NOVAS C 3.1 library from which SuperNOVAS is forked from.

Fixed

Fixes the NOVAS C 3.1 sidereal_time bug, whereby the sidereal_time() function had an incorrect unit cast.
Fixes antedating velocities and distances for light travel time in NOVAS C 3.1 ephemeris(). When getting positions and velocities for Solar-system sources, it is important to use the values from the time light originated from the observed body rather than at the time that light arrives to the observer. This correction was done properly for positions, but not for velocities or distances, resulting in incorrect observed radial velocities or apparent distances being reported for spectroscopic observations or for angular-physical size conversions.
Fixes NOVAS C 3.1 bug in ira_equinox() which may return the result for the wrong type of equinox (mean vs. true) if the equinox argument was changing from 1 to 0, and back to 1 again with the date being held the same. This affected NOVAS C 3.1 routines downstream also, such as sidereal_time().
Fixes NOVAS C 3.1 accuracy switching bug in cio_basis(), cio_location(), ecl2equ(), equ2ecl_vec(), ecl2equ_vec(), geo_posvel(), place(), and sidereal_time(). All these functions returned a cached value for the other accuracy if the other input parameters are the same as a prior call, except the accuracy.
Fixes multiple NOVAS C 3.1 bugs related to using cached values in cio_basis() with alternating CIO location reference systems. This affected many CIRS-based position calculations downstream.
Fixes NOVAS C 3.1 bug in equ2ecl_vec() and ecl2equ_vec() whereby a query with coord_sys = 2 (GCRS) has overwritten the cached mean obliquity value for coord_sys = 0 (mean equinox of date). As a result, a subsequent call with coord_sys = 0 and the same date as before would return the results GCRS coordinates instead of the requested mean equinox of date coordinates.
Some remainder calculations in NOVAS C 3.1 used the result from fmod() unchecked, which resulted in angles outside of the expected [0:2π] range and was also the reason why cal_date() did not work for negative JD values.
Fixes NOVAS C 3.1 aberration() returning NaN vectors if the ve argument is 0. It now returns the unmodified input vector appropriately instead.
Fixes unpopulated az output value in equ2hor() at zenith in NOVAS C 3.1. While any azimuth is acceptable really, it results in unpredictable behavior. Hence, we set az to 0.0 for zenith to be consistent.
Fixes potential NOVAS C 3.1 string overflows and eliminates associated compiler warnings.
Fixes the NOVAS C 3.1 ephem_close bug, whereby ephem_close() in eph_manager.c did not reset the EPHFILE pointer to NULL.
Supports calculations in parallel threads by making cached results thread-local.

Added

New debug mode and error traces. Simply call novas_debug(NOVAS_DEBUG_ON) or novas_debug(NOVAS_DEBUG_EXTRA) to enable. When enabled, any error conditions (such as NULL pointer arguments, or invalid input values etc.) will be reported to the standard error, complete with call tracing within the SuperNOVAS library, s.t. users can have a better idea of what exactly did not go to plan (and where). The debug messages can be disabled by passing NOVAS_DEBUF_OFF (0) as the argument to the same call.
Added Doxygen markup of source code and header.
Added Makefile for GNU make.
Added continuous integration on GitHub, including regression testing, static analysis, and doxygen validation.
Added an number of precompiler constants and enums in novas.h to promote consistent usage and easier to read code.
New runtime configurability:
- The planet position calculator function used by ephemeris() can be set at runtime via set_planet_provider(), and set_planet_provider_hp() (for high precision calculations). Similarly, if planet_ephem_provider() or planet_ephem_provider_hp() (defined in solsys-ephem.c) are set as the planet calculator functions, then set_ephem_provider() can set the user-specified function to use with these to actually read ephemeris data (e.g. from a JPL ephemeris file).
- If CIO locations vs GCRS are important to the user, the user may call set_cio_locator_file() at runtime to specify the location of the binary CIO interpolation table (e.g. cio_ra.bin) to use, even if the library was compiled with the different default CIO locator path.
- The default low-precision nutation calculator nu2000k() can be replaced by another suitable IAU 2006 nutation approximation via set_nutation_lp_provider(). For example, the user may want to use the iau2000b() model instead or some custom algorithm instead.
New intutitive XYZ coordinate conversion functions:
- for GCRS - CIRS - ITRS (IAU 2000 standard): gcrs_to_cirs(), cirs_to_itrs(), and itrs_to_cirs(), cirs_to_gcrs().
- for GCRS - J2000 - TOD - ITRS (old methodology): gcrs_to_j2000(), j2000_to_tod(), tod_to_itrs(), and itrs_to_tod(), tod_to_j2000(), j2000_to_gcrs().
New itrs_to_hor() and hor_to_itrs() functions to convert Earth-fixed ITRS coordinates to astrometric azimuth and elevation or back. Whereas tod_to_itrs() followed by itrs_to_hor() is effectively a just a more explicit 2-step version of the existing equ2hor() for converting from TOD to to local horizontal (old methodology), the cirs_to_itrs() followed by itrs_to_hor() does the same from CIRS (new IAU standard methodology), and had no prior equivalent in NOVAS C 3.1.
New ecl2equ() for converting ecliptic coordinates to equatorial, complementing existing equ2ecl().
New gal2equ() for converting galactic coordinates to ICRS equatorial, complementing existing equ2gal().
New refract_astro() complements the existing refract() but takes an unrefracted (astrometric) zenith angle as its argument.
New convenience functions to wrap place() for simpler specific use: place_star(), place_icrs(), place_gcrs(), place_cirs(), and place_tod().
New radec_star() and radec_planet() as the common point for existing functions such as astro_star() local_star(), virtual_planet(), topo_planet() etc.
New time conversion utilities tt2tdb(), get_utc_to_tt(), and get_ut1_to_tt() make it simpler to convert between UTC, UT1, TT, and TDB time scales, and to supply ut1_to_tt arguments to place() or topocentric calculations.
Co-existing solarsystem() variants. It is possible to use the different solarsystem() implementations provided by solsys1.c, solsys2.c, solsys3.c and/or solsys-ephem.c side-by-side, as they define their functionalities with distinct, non-conflicting names, e.g. earth_sun_calc() vs planet_jplint() vs planet_eph_manager() vs planet_ephem_provider().
New novas_case_sensitive(int) to enable (or disable) case-sensitive processing of object names. (By default NOVAS object names are converted to upper-case, making them effectively case-insensitive.)
New make_planet() and make_ephem_object() to make it simpler to configure Solar-system objects.

Changed

Changed to support for calculations in parallel threads by making cached results thread-local (as opposed to the globally cached values in NOVAS C 3.1). This works using the C11 standard _Thread_local or else the earlier GNU C >= 3.3 standard __thread modifier. You can also set the preferred thread-local keyword for your compiler by passing it via -DTHREAD_LOCAL=... in config.mk to ensure that your build is thread-safe. And, if your compiler has no support whatsoever for thread_local variables, then SuperNOVAS will not be thread-safe, just as NOVAS C isn’t.
SuperNOVAS functions take enums as their option arguments instead of the raw integers in NOVAS C 3.1. These enums are defined in novas.h. The same header also defines a number of useful constants. The enums allow for some compiler checking, and make for more readable code that is easier to debug. They also make it easy to see what choices are available for each function argument, without having to consult the documentation each and every time.
All SuperNOVAS functions check for the basic validity of the supplied arguments (Such as NULL pointers or illegal duplicate arguments) and will return -1 (with errno set, usually to EINVAL) if the arguments supplied are invalid (unless the NOVAS C API already defined a different return value for specific cases. If so, the NOVAS C error code is returned for compatibility). There were no such checks performed in NOVAS C 3.1.
All erroneous returns now set errno so that users can track the source of the error in the standard C way and use functions such as perror() and strerror() to print human-readable error messages. (NOVAS C 3.1 did not set errno).
Many output values supplied via pointers are set to clearly invalid values in case of erroneous returns, such as NAN so that even if the caller forgets to check the error code, it becomes obvious that the values returned should not be used as if they were valid. (No more sneaky silent errors, which were common in NOVAS C 3.1.)
Many SuperNOVAS functions allow NULL arguments (unlike NOVAS C 3.1), both for optional input values as well as outputs that are not required (see the API Documentation for specifics). This eliminates the need to declare dummy variables in your application code for quantities you do not require.
All SuperNOVAS functions that take an input vector to produce an output vector allow the output vector argument be the same as the input vector argument (unlike in NOVAS C 3.1 where this was not consistently implented). For example, frame_tie(pos, J2000_TO_ICRS, pos) using the same pos vector both as the input and the output. In this case the pos vector is modified in place by the call. This can greatly simplify usage, and can eliminate extraneous declarations, when intermediates are not required.
SuperNOVAS declares function pointer arguments as const whenever the function does not modify the data content being referenced. This supports better programming practices that generally aim to avoid unintended data modifications. (The passing of const arguments to NOVAS C 3.1 calls would result in compiler warnings.)
Catalog names can be up to 6 bytes (including termination), up from 4 in NOVAS C 3.1, while keeping struct layouts the same as NOVAS C thanks to alignment, thus allowing cross-compatible binary exchange of cat_entry records with NOVAS C 3.1.
Object ID numbers are long instead of short (in NOVAS C 3.1) to accommodate NAIF IDs, which require minimum 32-bit integers.
precession() can now take arbitrary input and output epochs. Unlike NOVAS C 3.1, it is not required that either of those epochs be J2000.
cel2ter() and ter2cel() can now process ‘option’/’class’ = 1 (NOVAS_REFERENCE_CLASS) regardless of the methodology (EROT_ERA or EROT_GST) used to input or output coordinates in GCRS (unlike in NOVAS C 3.1).
Changed make_object() to retain the specified number argument (which can be different from the starnumber value in the supplied cat_entry structure), in contrast to NOVAS C 3.1, which set object->number to 0 for cat_entry arguments.
cio_location() will always return a valid value as long as neither output pointer argument is NULL. (NOVAS C 3.1 would return an error if a CIO locator file was previously opened but cannot provide the data for whatever reason).
sun_eph() in solsysl3.c evaluates the series in reverse order compared to NOVAS C 3.1, accumulating the least significant terms first, and thus resulting in higher precision result in the end.
Changed vector2radec() to return NAN values if the input is a null-vector (i.e. all components are zero), as opposed to NOVAS C 3.1, which left the input vector argument unchanged.
IAU 2000A nutation model uses higher-order Delaunay arguments provided by fund_args(), instead of the linear model in NOVAS C 3.1.
IAU 2000 nutation made a bit faster vs NOVAS C 3.1, via reducing the the number of floating-point multiplications necessary by skipping terms that do not contribute. Its coefficients are also packed more frugally in memory, resulting in a smaller footprint than in NOVAS C 3.1.
More efficient paging (cache management) for cio_array() vs NOVAS C 3.1, including I/O error checking.
Changed the standard atmospheric model for (optical) refraction calculation to include a simple model for the annual average temperature at the site (based on latitude and elevation). This results is a slightly more educated guess of the actual refraction than the global fixed temperature of 10 °C assumed by NOVAC C 3.1 regardless of observing location.

Deprecated

novascon.h / novascon.c: These definitions of constants in NOVAS C 3.1 was troublesome for two reasons: (1) They were primarily meant for use internally within the library itself. As the library clearly defines in what units input and output quantities are expressed, the user code can apply its own appropriate conversions that need not match the internal system used by the library. Hence exposing these constants to users was half baked. (2) The naming of constants was too simplistic (with names such as C or F) that it was rather prone to naming conflicts in user code. As a result, the constants have been moved to novas.h with more unique names (such as NOVAS_C and NOVAS_EARTH_FLATTENING. New code should rely on these definitions instead of the troubled constants of novascon.c / .h if at all necessary.
equ2hor(): It’s name does not make it clear that this function is suitable only for converting TOD (old methodology) to horizontal but not CIRS to horizontal (IAU 2000 standard). You should use the equivalent but more specific tod_to_itrs() or the newly added cirs_to_itrs(), followed by itrs_to_hor() instead.
cel2ter() / ter2cel(): These NOVAS C 3.1 function can be somewhat confusing to use. You are likely better off with tod_to_itrs() and cirs_to_itrs() instead, and possibly followed by further conversions if desired.
app_star(), app_planet(), topo_star() and topo_planet(): These NOVAS C 3.1 function use the old (pre IAU 2000) methodology, which isn’t clear from their naming. Use place() or place_star() with NOVAS_TOD or NOVAS_CIRS as the system instead, as appropriate.
readeph(): This NOVAS C 3.1 function is prone to memory leaks, and not flexible with its origin (necessarily at the barycenter). Instead, use a similar novas_ephem_provider implementation and set_ephem_provider() for a more flexible and less troublesome equivalent, which also does not need to be baked into the library and can be configured at runtime.
tdb2tt(). Use tt2tdb() instead. It’s both more intuitive to use (returning the time difference as a double) and faster to calculate than the NOVAS C function, not to mention that it implements the more standard approach.