This Fortran facility provides a means to find local extrema of a map in HEALPix format. It also serves to illustrate the use of the following parts of the HEALPix toolkit: fast neighbour and extrema finding in the nested scheme, in-place conversion between RING and NESTED pixel schemes

Location in HEALPix directory tree: src/f90/hotspot/HotSpots.F90 


% hotspot


infile =
Defines the input map file.
extrema_outfile =
Defines the output map file.
maxima_outfile =
Defines the output ascii list of maxima.
minima_outfile =
Defines the output ascii list of minima.


hotspot reads a healpix map in FITS format and generates the following outputs: 1) a HEALPix map in FITS format which is zero everywhere, except at pixels which contain local extrema. These pixels have the same values as in the input map. 2) an ASCII file which lists the pixel numbers and values of maxima, and 3) an ASCII file which lists the pixel numbers and values of minima.

The facility can be used in both an interactive mode and a command mode, where command qualifiers are fed to the facility using an input file.

Note the following limitations: hotspot (and the toolkit neighbour finder which it uses) will only work on maps with $N_{side}\ge 2$.


The following datasets are involved in the hotspot processing.

Dataset Description
None required


This section lists those routines and facilities (including those external to the HEALPix distribution) which can assist in the utilisation of hotspot.

This HEALPix facility can generate a FITS format sky map to be input to hotspot.
This HEALPix Fortran facility can be used to visualise the output map.
This HEALPix IDL facility can be used to visualise the output map.


hotspot runs in interactive mode.


hotspot filename
When `filename' is present, hotspot enters the non-interactive mode and parses its inputs from the file `filename'. This has the following structure: the first entry is a qualifier which announces to the parser which input immediately follows. If this input is omitted in the input file, the parser assumes the default value shown below. If the equality sign is omitted, then the parser ignores the entry. In this way comments may also be included in the file. In this example, the file contains the following qualifiers:
infile= map.fits
extrema_outfile= pixlminmax.fits
maxima_outfile= maxima.dat
minima_outfile= minima.dat
hotspot reads in the map `map.fits' and generates an output map with name `pixlminmax.fits', and two ASCII files, `maxima.dat' and `minima.dat'.


* Initial release (HEALPix 0.90)
* Optional non-interactive operation. Proper FITS file support for input and output maps. (HEALPix 1.00)


This section describes error messages generated by hotspot

Message Severity Text
can not allocate memory for array xxx Fatal You do not have sufficient system resources to run this facility at the map resolution you required. Try a lower map resolution.

Version 3.31, 2017-01-06