Many previous VHE gamma-ray developers are familiar with the CERN ROOT library for data processing. ctapipe is intentionally not ROOT based, and we do not allow ROOT or pyroot as a required dependency of ctapipe due to its large and complex nature and maintenence issues. Fortunately nearly all ROOT-like functionality can be found in the scientific python stack, though the API is of course not the same.
To help developers familiar only with ROOT migrate to the scientific python stack, the following table can be helpful:
| ROOT functionality | Recommended Python Equivalent |
|---|---|
| interactive interpreter | ipython, jupyter notebook |
| TH1D,TH2D,TH3D | numpy.ndarray + numpy.histogramdd() |
| TProfile | numpy.ndarray |
| TGraph | numpy.ndarray + matplotlib plots |
| TTree | astropy.table, pandas, pytables |
| ROOT File format (TFile) | HDF5 (pytables) |
| TMinuit | scipy.optimize or iminuit |
| 2D/3D graphics | matplotlib or bokeh |
| TMVA | scikit-learn |
| GUI | various (wxwidgets, Qt,gtk) |
| AstroROOT | astropy.io.fits or fitsio |
| ROOFit | astropy.modelling or lmfit |
| Reflex, CINT | not needed |
| TMatrix, etc | numpy.ndarray + scipy.linalg |
| TMatrixTSparse | scipy.sparse |
| TList | list |
| TArray, TObjArray | list |
| TMap, THashList | dict |
| TRandom | numpy.random + scipy.stats |
| Math, MathMore | numpy + scipy |
| Script compilation | Numba, Cython |
| ROOT::Math::VirtualIntegrator | scipy.integrate |
| Access to external C++ code | cython, ctypes |
| – | astropy.coordinates |
| – | astropy.units |
| – | astropy.time |
| – | astropy.wcs (projections) |
| – | numpy.ndarray (n-dimensional tables) |
| – | scipy.interpolate.interpnd (n-dimensional interpolation) |
| – | scipy.signal (digital signal processing) |