lsst.meas.algorithms.skyObjects Namespace Reference

Classes
class	SkyObjectsConfig
class	SkyObjectsTask

Functions
def	generateSkyObjects (mask, seed, config)

Function Documentation

generateSkyObjects()

def lsst.meas.algorithms.skyObjects.generateSkyObjects	(		mask,
			seed,
			config
	)

Generate a list of Footprints of sky objects

Sky objects don't overlap with other objects. This is determined
through the provided `mask` (in which objects are typically flagged
as `DETECTED`).

The algorithm for determining sky objects is random trial and error:
we try up to `nTrialSkySources` random positions to find `nSources`
sky objects.

Parameters
----------
mask : `lsst.afw.image.Mask`
    Input mask plane, which identifies pixels to avoid for the sky
    objects.
seed : `int`
    Random number generator seed.
config : `SkyObjectsConfig`
    Configuration for finding sky objects.

Returns
-------
skyFootprints : `list` of `lsst.afw.detection.Footprint`
    Footprints of sky objects. Each will have a peak at the center
    of the sky object.

Definition at line 29 of file skyObjects.py.

def generateSkyObjects(mask, seed, config):
    """Generate a list of Footprints of sky objects

    Sky objects don't overlap with other objects. This is determined
    through the provided `mask` (in which objects are typically flagged
    as `DETECTED`).

    The algorithm for determining sky objects is random trial and error:
    we try up to `nTrialSkySources` random positions to find `nSources`
    sky objects.

    Parameters
    ----------
    mask : `lsst.afw.image.Mask`
        Input mask plane, which identifies pixels to avoid for the sky
        objects.
    seed : `int`
        Random number generator seed.
    config : `SkyObjectsConfig`
        Configuration for finding sky objects.

    Returns
    -------
    skyFootprints : `list` of `lsst.afw.detection.Footprint`
        Footprints of sky objects. Each will have a peak at the center
        of the sky object.
    """
    if config.nSources <= 0:
        return []

    skySourceRadius = config.sourceRadius
    nSkySources = config.nSources
    nTrialSkySources = config.nTrialSources
    if nTrialSkySources is None:
        nTrialSkySources = config.nTrialSourcesMultiplier*nSkySources

    box = mask.getBBox()
    box.grow(-(int(skySourceRadius) + 1))  # Avoid objects partially off the image
    xMin, yMin = box.getMin()
    xMax, yMax = box.getMax()

    avoid = lsst.afw.geom.SpanSet.fromMask(mask, mask.getPlaneBitMask(config.avoidMask))
    if config.growMask > 0:
        avoid = avoid.dilated(config.growMask)

    rng = lsst.afw.math.Random(seed=seed)

    skyFootprints = []
    for _ in range(nTrialSkySources):
        if len(skyFootprints) == nSkySources:
            break

        x = int(rng.flat(xMin, xMax))
        y = int(rng.flat(yMin, yMax))
        spans = lsst.afw.geom.SpanSet.fromShape(int(skySourceRadius), offset=(x, y))
        if spans.overlaps(avoid):
            continue

        fp = lsst.afw.detection.Footprint(spans, mask.getBBox())
        fp.addPeak(x, y, 0)
        skyFootprints.append(fp)

    return skyFootprints