# 3.1.20. Obin: optimal rebinning of the data¶

## 3.1.20.1. Overview¶

This command rebins (a part of) the data (thus both the spectrum and the response) to the optimal bin size given the statistics of the source as well as the instrumental resolution. This is recommended to do in all cases, in order to avoid oversampling of the data. The theory and algorithms used for this rebinning are described in detail in Optimal definition of respons matrices. A simple cartoon of this is: binning to 1/3 of the FWHM, but the factor of 1/3 depends weakly upon the local count rate at the given energy and the number of resolution elements. The better the statistics, the smaller the bin size.

Note

Usually, the ignore command and the obin command are used around the same time. The safest order is to ignore parts of the spectrum first and then re-bin it. If the bin command is done first and then parts of the spectrum are ignored using a different energy range, then bins at the edges of the energy range could end up being reduced in width.

## 3.1.20.2. Syntax¶

The following syntax rules apply:

`obin #i1:` : Simplest command allowed. #i1: is the range in data channels over which the binning needs to take place.
`obin #r1: #i: unit #a` : The same command as above, except that now the ranges over which the data is to be binned (#r1:) are specified in units (#a) different from data channels. These units can be eV, keV, Å, as well as in units of Rydberg (ryd), Joules (j), Hertz (hz) and nanometers (nm).
`obin [instrument #i1:] [region #i2:] #i3:` : Here #i3: is the same as #i1: in the first command. However, here one can specify the instrument range #i1: and the region range #i2: as well, so that the binning is done only for one given data set.
`obin [instrument #i1:] [region #i2:] #r1: [unit #a]` : This command is the same as the above, except that here one can specify the range over which the binning should occur in the units specified by #a. These units can be eV, Å, keV, as well as in units of Rydberg (ryd), Joules (j), Hertz (hz) and nanometers (nm).

## 3.1.20.3. Examples¶

`obin 1:10000` : Optimally bins the data channels 1:10000.
`obin 1:4000 unit ev` : Does the same as the above, but now the data range to be binned is given in eV, from 1 4000 eV, instead of in data channels.
`obin instrument 1 region 1 1:19 unit a` : Bins the data from instrument 1 and region 1 between 1 and 19 Å.