Skip to content. | Skip to navigation

Personal tools
You are here: GES DISC Home Giovanni - Interactive Visualization and Analysis Additional Features Users Manual Giovanni Operation Technical Summary: Histogram

Giovanni Operation Technical Summary: Histogram

Histogram / Histogram, Area-averaged / Histogram, Time-averaged

The Histogram service represents parameter data values in an output visualization (a Lat-lon map or time-series) by depicting the distribution of the selected parameter data  — the number of times (frequency) that values of the parameter occur —   in the output visualization.    The histogram will appear as a set of vertical bars where the height of each bar (and the Y-axis) indicates the number of ocurrences of parameter values in a certain range.     The range values will be shown on the X-axis.


Input Values

The Histogram service will operate on all parameter values in a generated Lat-lon map or time-series.   The actual data used for the visualization output is contained in an HDF4 data array output file.



  • GIF image of the histogram bar plot
  • Corresponding HDF data file array with the summed occurrences of the data parameter values in each data range.


Calculation Details

The Histogram service calculates the density distribution of a set of elements in an array. The array elements are divided such that they fall into a bin of some width between a minimum and maximum value. The histogram can be represented by the function:

 Histogram equation

where n is the total number of bins in the sample, and where xi is the ith bin whose elements have a value equal to i. In Giovanni the default number of bins is arbitrarily set to n = 50, with the minimum and maximum values set to the dynamic range of the data (unless optimal minimum and maximum values are pre-defined).


Histogram Service Types


Histogram: No averaging (calculation of mean values) is involved.  The histogram is produced using all of the grid points in the selected region and time interval.   This histogram type is for a single discrete time interval, which could be a 3-hour, one day, or one month period. 

Histogram of Lat-lon plot

Histogram, Area-averaged: If a histogram of a time-series is desired, the spatial region is first averaged for each time interval, and the histogram for each time interval is produced.

 Histogram of area-averaged time-series

Histogram, Time-averaged:  If the data span multiple time intervals (i.e., hourly, 3-hour, day, or month), the values at each grid point are first averaged over time, and then the resulting histogram is derived for the selected area.   This is similar to the way that a time-averaged lat-lon map is calculated, except in this case the output values will be depicted as the histogram rather than being mapped as averaged values.

 Histogram, time-averaged


Document Actions
NASA Logo -
NASA Privacy Policy and Important Notices
Last updated: Apr 06, 2016 04:17 PM ET