The Small Bodies Geophysical Analysis Tool (SBGAT) implementation.

• SBGAT's classes inherit from VTK's filters so as to facilitate manipulation and visualization tasks. SBGAT comes in the form of a backend library SbgatCore and a frontend component SbgatGui exposing SbgatCore's classes through a GUI.

• The latest stable release of SBGAT can be retrieved from the master branch of the present repository, or by using Homebrew as described below.

• The develop branch features code that is undergoing active development or debugging.

The SBGAT User's Wiki can be found here, and the technical documentation here

Homebrew can be used to install SBGAT's components and dependencies.

brew tap bbercovici/self
brew update
brew install sbgat-core
brew install sbgat-gui

The SbgatGui executable will be simlinked to /usr/local/bin .

Refer to the detailed installation instructions.

Assuming that SbgatCore was installed with Homebrew:

brew update
brew upgrade sbgat-core

If installed, after updating Homebrew, SbgatGui can be also upgraded:

brew upgrade sbgat-gui

Check each of SBGAT's dependencies repository and SBGAT's repository itself for updates. Assuming that the current directory is the original Git local repository for the component you wish to update, run :

git pull
cd build
cmake ..
make
make install

to apply the update (if any).

• Uncertainty quantification in the surface polyhedron gravity model can now be computed from within SBGATGui

• Users now must load one shape model in SBGATGui before being able to open up any of the analyses/observations windows.

• SBGATMassPropertiesUQ's master script has been corrected with the proper SIM_PREFIX

• Introduced two new base classes, SBGATFilter and SBGATFilterUQ, the latter being tailored for uncertainty quantification in the considered geophysical properties
• A Python script producing shape "slices" has been added

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develop

• SBGATMassProperties now inherits from SBGATFilter
• SBGATPolyhedronGravityModel now inherits from SBGATMassProperties
• SBGATMassPropertiesUQ now inherits from SBGATFilterUQ
• SBGATPolyhedronGravityModelUQ now inherits from SBGATMassPropertiesUQ
• Clicking on a facet in SbgatGui now results in displaying the facet center coordinates.
• Populated Examples folder with illustrative snippets for SBGATPolyhedronGravityModelUQ and SBGATMassPropertiesUQ. These tests should be run from a Python 3 process (run ../master_script.py) called from their build directory.

• As of April 7th 2019, OpenMP is no longer found by CMake on Mac.

• SBGAT 2.02.4 introduces SBGATPolyhedronGravityModelUQ, a class dedicated to uncertainty quantification in Polyhedron Gravity potentials and accelerations arising from a stochastic shape. This class enables the evaluation of the variance in the potential and covariance in the acceleration at any point in space (excluding shape edges)
• Expanded and consolidated the Tests suite.

• Length unit consistency has been completely overhauled.
  • All of SBGAT's filters (SBGATMassproperties, SBGATSphericalHarmo, SBGATPolyhedronGravityModel,...) will return results using meters as length unit. For instance, calling GetAcceleration from the SBGATPolyhedronGravityModel class will always return an acceleration in m/s^2.
  • Similarly, any method from the aforementioned filters expects an input position to be expressed in meters.
  • Classes documentation has been updated to reflect this change
  • Overall consistency is enforced by manually specifying the unit in which a given shape model is specified through the use of SetScaleMeters or SetScaleKiloMeters. This way, a shape whose coordinates are expressed in kilometers can be connected to an instance of SBGATMassproperties or any other filter and used in a completely transparent manner as long as SetScaleKiloMeters is called on the filter before Update()
  • SBGATMassproperties, SBGATSphericalHarmo and SBGATPolyhedronGravityModel are initialized by default for a shape whose length units are in meters (i.e the scaleFactor member is set to 1 by default, and set to 1000 if SetScaleKiloMeters() is called)
• NO MORE "UPDATE()" FROM GETTERS
• Work is in progress to revamp the main page of the doxygen documentation

• Fixed bug in SBGATSphericalHarmo that could have caused the evaluation of the spherical harmonics over a non-barycentered shape to be incorrect.
• Pushed fix to latest version of SHARMLib dependency to address the same issue
• Modified CMakeLists.txt in Tests to fix issue caused by a conflicting header being sometimes included by one of VTK's dependencies

• Shape models can now be modified from within SBGATGui, by selecting a vertex and applying a Gaussian interpolation of the vertex displacement to a k-neighbor neighborhood.

• Camera is now positioned at the correct distance from the targeted shape body upon loading
• Improved visual aspect of selected facet
• Improved visual aspect of loaded shapes

• Fixed bug in SBGATGui that prevented proper alignment of the shape model with its principal axes

• Second-moments about the mean in the volume, center-of-mass, unit-densiy inertia tensor, principal moments, principal dimensions and orientation of the principal axes can now be evaluated through the static methods of SBGATShapeUncertainty
• SBGATShapeUncertainty provides two methods to evaluate the statistical moments: a monte-carlo method ComputeInertiaStatisticsMC, and another method ComputeInertiaStatistics leveraging a linearized uncertainty model as proposed by Bercovici and McMahon (Inertia statistics of an uncertain small body shape, ICARUS 2019 (In Review). Both methods take the same argument (correleation length l and the standard deviation governing the error in the control point coordinates, directed along the average normal at these points). Both these methods assume that the shape error can be described as normally distributed and zero-mean.
• Added a new function in Tests to illustrate the convergence of the Monte-Carlo shape uncertainty sampling to the analytical prediction

• SBGATMassProperties::SaveMassProperties is now saving the average radius (r_avg = cbrt(3/4 *Volume/pi)) to the JSON file
• SBGATMassproperties::GetPrincipalAxes could return 4 dcms, all representative of the same inertia ellipsoid. To enforce stability in the principal axes extractions, SBGATMassproperties::GetPrincipalAxes now returns the dcm that has the smallest-norm corresponding MRP.
• SBGAT will try to link against OpenMP by default. This behaviour can now be disabled by passing the --without-libomp flag to Homebrew or by passing the -DNO_OMP:BOOL=TRUE flag to CMake

• Fixed potential bug in SBGATPolyhedronGravityModel involving a parallel computing block where a variable with no viable reduction clause was being operated on
• SBGATMassproperties::GetPrincipalAxes is now returning the DCM [PB] converting from the body coordinate frame to the body principal frame. It was previously returning [BP]

Note that ShapeUQLib is now a dependency of SBGAT and should be installed prior to compiling the newest SBGATCore and SBGATGui. Instructions are provided on the corresponding wiki page.

• SBGATMassProperties now offers a method to save the computed mass properties to a JSON file (SBGATMassProperties::SaveMassProperties)
• A static method evaluating and saving the mass properties of the provided shape is now provided (SBGATMassProperties::ComputeAndSaveMassProperties)
• The Measures menu in SbgatGUI has been augmented with a Save geometric measures action

• The inertia tensor normalization has changed. When computing the mass properties of a given small body, the following normalization is now applied to the inertia tensor: I_norm = I / (mass * r_avg ^ 2) where r_avg = cbrt(3/4 *Volume/pi). r_avg is now computed along with the other properties within SBGATMassProperties.
• The parallel axis theorem is no-longer applied to the small body. That is, the inertia will always be expressed about (0,0,0).
• Several GUI minors bug fixes

• Facets can now be individually selected in SbgatGui by clicking on them. If the surface PGM of the selected shape is available, the results for the selected facet will be shown in the console

• The Set Shape Mapper option was renamed to Set Results Overlay
• Several GUI minors bug fixes

• Fixed bug in SbgatCore that was due to an unecessary rescaling of the computed potentials and accelerations within SbgatCore::ComputeSurfacePGM. This bug was manifesting itself when calling SbgatCore::ComputeSurfacePGM with a shape model whose coordinates were expressed in kilometers. This bug was not affecting SbgatGui since it automatically rescales input shapes to meters upon loading.

• A previously evaluated surface Polyhedron Gravity Model can now be loaded from a JSON file via the static method SBGATPolyhedronGravityModel::LoadSurfacePGM
• SbgatGui can now overlay previously computed surface PGM results over a corresponding shape model (aka featuring the same number of facets as the one used to generate the surface PGM)

• The surface polyhedron gravity model now computes:
  • gravitational slopes
  • inertial gravity potentials
  • body-fixed gravity potentials
  • inertial gravity acceleration magnitudes
  • body-fixed gravity acceleration magnitudes

• The gravity-gradient matrix deriving from the polyhedron gravity model can now be evaluated
• The evaluation of the surface polyhedron gravity model can now be saved to a JSON file through SBGATPolyhedronGravityModel::SaveSurfacePGM
• This static method is available in SbgatGUI as the evaluation of the PGM will now require the specification of an output file

• Stronger typing of inputs in SBGATPolyhedronGravityModel
• SbgatGui will now ask users whethers a loaded shape should be barycentered/principal-axis aligned, and apply the corresponding transform if answered yes

• The gravity-gradient matrix deriving from the spherical harmonics gravity model can now be evaluated.
• The partial derivative of the spherical harmonics gravity model with respect to the gravity spherical harmonics coefficients can now be evaluated.
• A static method SBGATPolyhedronGravityModel::ComputeSurfacePGM has been added to SbgatCore to facilitate the evaluation of the polyhedron gravity model at the surface of a small body shape.

• The CMake configuration of SBGAT will no longer failed if OpenMP cannot be found.
• A warning will now be issued in SbgatGui if the surface polyhedron gravity model is evaluated with a zero rotation period.
• SBGATPolyhedronGravityModel and SBGATSphericalHarmo are now returning potentials and accelerations evaluated with the same unit of length as the shape model they were associated with.

• Fixed bug in SbgatGui that was due to a vtkPolydataMapper not being properly assigned to the correct ModelDataWrapper after aligning the shape

• The Polyhedron Gravity Model can now be evaluated at the surface of loaded shape models from SbgatGuis
• The surface PGM can then be overlaid in the form of surface slopes, gravitional potential, inertial and body-fixed accelerations

• The SBGAT documentation should be back online at the following location

• Fixed a major regression that was causing SbgatGui to crash when computing lightcurves

• Built-from source GCC no longer required for OpenMP support on Mac since CLANG 10 now provides the required definitions
• Added a method simultaneously computing gravity potential and acceleration in SBGATPolyhedronGravityModel and updated corresponding tests

• Added constant qualifiers to SBGATPolyhedronGravityModel inputs

• Captions should now properly show in SbgatGui

• Created SBGATObs base-class from which SBGATObsLightcurve and SBGATObsRadar derive
• Added new functionalities to SbgatGui
• Created the dependency OrbitConversions to generate Keplerian trajectories or convert 6 dof states between Cartesians and Keplerian representations.

• SBGATObsLightcurve and SBGATObsRadar now handle primary/secondary asteroid systems, allowing generation of lightcurves and radar observations of binary asteroid systems. Relative trajectories can be computed under the assumption that the secondary is undergoing a keplerian orbit about the primary, or be loaded from an external file.
• Removed dependency of SBGATSphericalHarmo to density and mass of the considered shape model

• Fixed a bug in SBGATPolyhedronGravityModel.cpp where the edge extraction would sometimes fail. Fix consisted in filtering the input through a vtkPolyDataCleaner before handing it to vtkExtractEdges.

• Added SBGATObsLightcurve to SbgatCore , a module enabling the generation of instantaneous-exposure lightcurves in a fixed-spin scenario. This module assumes constant small-body spin and phase angle between the sun, the small body and the observer.
• SBGATObsRadar now throws an instance of std::runtime_error if the specified bin sizes are incompatible with the collected data that may yield an empty histogram dimension
• Observations from SBGATObsRadar and SBGATObsLightcurve can be penalized by incidence so as to diminish the weight of a given measurement. SBGATObsRadar weighs by the cos of the angle between the observer and the surface normal, while SBGATObsLightcurve weighs by the product of the cos of the angle between the observer and the surface normal and the cos of the angle between the sun and the surface normal

• Simulated Range/Range-rate images and lightcurves rely on area-weighted surface sampling : N * surface_area/max_surface_area points are sampled for each facet, where max_surface_area is the surface area of the largest facet in the shape and surface_area that of the considered facet
• Removed more deprecated functionalities

• Fixed bug in SbgatGui that was allowing users to bin radar observations before effectively collecting them.
• Saved radar images now have correct color levels

• Adds SBGATObsRadar to SbgatCore, a class emulating range/range-rate radar measurements. The corresponding menu and action are also available in SbgatGui
• If gcc exists in Homebrew's Cellar, SBGAT and its dependencies will be compiled using this OpenMP compliant compiler, giving better performance on multithreaded platforms. This functionality had to be postponed due to Qt 5.10 incompability with recent gcc versions on MacOS.

This new release of SBGAT allows import/export of gravity spherical harmonics from/into SBGAT by means of Niels Lohmann's Modern C++ JSON library. This functionality is available from SbgatCore's classes and SbgatGui as well.

• SBGAT 1.04.3 marks the shift to the Homebrew package manager as a way to greatly facilitate SBGAT's distribution and update. It is of course still possible to download each of SBGAT's dependencies separatly and manually build from source.

• SBGAT 1.04.2 enables the computation of the spherical harmonics expansion directly from SbgatGUI

  • Added an action Compute Gravity Spherical Harmonics under Analyses
  • Added an action Align Shape under Small Body. This action aligns the barycenter of the selected shape with (0,0,0) and its principal axes with the rendering window axes. This is a prerequisite for meaningful YORP or gravity spherical harmonics computations.
  • Added an action Save Shape Model under Small Body. This action exports the selected shape model in its current state to an .obj file of choice.

Users must update their versions of RigidBodyKinematics to reflect the latest changes

• SBGAT and its dependencies are now distributed under the MIT license.
• No new functionalities besides updated license information.

• SBGAT 1.04.0 can now be used to compute the spherical harmonics expansion of the exterior gravity field about a constant-density polyhedron

  • Added SBGATSphericalHarmo, a SBGAT filter enabling the computation and evaluation of the spherical harmonics coefficients of the exterior gravity field caused by a constant density shape represented by a vtkPolydata. This class effectively provides a wrapper around SHARMLib, a library developed by Benjamin Bercovici from the original works of Yu Takahashi and Siamak Hesar at the University of Colorado Boulder. For more details, see Spherical harmonic coefficients for the potential of a constant-density polyhedron by Werner, R. a. (1997).
  • Added a test where the spherical harmonics expansion is computed and evaluated around KW4. The test succeeds if the acceleration error relative to the polyhedron gravity model is less that 0.0001 %

Note that SHARMLib is now a dependency of SBGAT and should be installed prior to compiling the newest SBGATCore and SBGATGui. Instructions are provided on the corresponding wiki page.

• SBGAT 1.03.0 sees the introduction of YORP coefficients computation

  • Added SBGATSrpYorp, a SBGAT filter enabling the computation of the YORP force and torque Fourier coefficients from a VTK Polydata. This class effectively provides a wrapper around YORPLib, a library developed by Jay W. McMahon at the University of Colorado Boulder that implements the analytical results derived in The dynamical evolution of uniformly rotating asteroids subject to YORP by Scheeres, D. J. (2007).
  • YORP coefficients computation can be performed from within SBGATGui through the Analyses drop-down menu.

Note that YORPLib is now a dependency of SBGAT and should be installed prior to compiling the latest SBGATCore and SBGATGui. Instructions are provided on the corresponding wiki page.

• SBGAT 1.02.1 marks the transition to VTK as SBGAT's backbone.

  • Added SBGATMassProperties, a SBGAT filter computing the surface area, volume, inertia and center of mass of a constant density polyhedron (see Dobrovolskis, A. R. (1996). Inertia of Any Polyhedron. Icarus, 124, 698–704. )
  • Added SBGATPolyhedronGravityModel, a SBGAT filter computing the acceleration and potential of a constant density, topologically-closed polyhedron polyhedron (see Werner, R.A. & Scheeres, D.J. Celestial Mech Dyn Astr (1996) 65: 313.)
  • Added validation tests

• SBGAT 1.02 is a first take at fully leveraging VTK data structures for visual props representation and operation. Current features of SBGATGui include:
  • Small body shape model import from .obj files
  • Trajectory loaded from time-XYZ ascii files. This capability may eventually be replaced by SPICE kernels
  • Spacecraft shape model import from .obj files
  • Spacecraft displacement along previously loaded trajectory
  • Addition/removal of light sources at arbitrary positions
  • Computation of geometric measures such as surface area, volume, bounding boxes, center-of-mass and inertia tensor, the last two assuming a constant density distribution

The SBGAT code documentation can be found here. It was generated with Doxygen and hosted on GitHub using the method described here

This software is distributed under the MIT License

Created by Benjamin Bercovici