find_peaks#

gammapy.estimators.utils.find_peaks(image, threshold, min_distance=1)[source]#

Find local peaks in an image.

This is a very simple peak finder, that finds local peaks (i.e. maxima) in images above a given threshold within a given min_distance around each given pixel.

If you get multiple spurious detections near a peak, usually it’s best to smooth the image a bit, or to compute it using a different method in the first place to result in a smooth image. You can also increase the min_distance parameter.

The output table contains one row per peak and the following columns:

x and y are the pixel coordinates (first pixel at zero).
ra and dec are the RA / DEC sky coordinates (ICRS frame).
value is the pixel value.

It is sorted by peak value, starting with the highest value.

If there are no pixel values above the threshold, an empty table is returned.

There are more featureful peak finding and source detection methods e.g. in the photutils or scikit-image Python packages.

Parameters:

imageWcsNDMap: Image like Map.
thresholdfloat or array-like: The data value or pixel-wise data values to be used for the detection threshold. A 2D threshold must have the same shape as the map data.
min_distanceint or Quantity: Minimum distance between peaks. An integer value is interpreted as pixels. Default is 1.

Returns:

outputTable: Table with parameters of detected peaks.

Examples

>>> import astropy.units as u
>>> from gammapy.datasets import MapDataset
>>> from gammapy.estimators import ExcessMapEstimator
>>> from gammapy.estimators.utils import find_peaks
>>>
>>> dataset = MapDataset.read("$GAMMAPY_DATA/cta-1dc-gc/cta-1dc-gc.fits.gz")
>>> estimator = ExcessMapEstimator(
...     correlation_radius="0.1 deg", energy_edges=[0.1, 10] * u.TeV
... )
>>> maps = estimator.run(dataset)
>>> # Find the peaks which are above 5 sigma
>>> sources = find_peaks(maps["sqrt_ts"], threshold=5, min_distance="0.25 deg")
>>> print(sources)
value   x   y      ra       dec
                  deg       deg
------ --- --- --------- ---------
32.191 161 118 266.41924 -28.98772
  18.7 125 124 266.80571 -28.14079
9.4498 257 122 264.86178 -30.97529
9.3784 204 103 266.14201 -30.10041
5.3493 282 150 263.78083 -31.12704