TractInfo

class lsst.skymap.TractInfo(id, patchInnerDimensions, patchBorder, ctrCoord, vertexCoordList, tractOverlap, wcs)

Bases: object

Information about a tract in a SkyMap sky pixelization

Parameters:
id : int

tract ID

patchInnerDimensions : tuple of int

Dimensions of inner region of patches (x,y pixels).

patchBorder : int

Overlap between adjacent patches (in pixels)

ctrCoord : lsst.geom.SpherePoint

ICRS sky coordinate of center of inner region of tract; also used as the CRVAL for the WCS.

vertexCoordList : list of lsst.geom.SpherePoint

Vertices that define the boundaries of the inner region.

tractOverlap : lsst.geom.Angle

Minimum overlap between adjacent sky tracts; this defines the minimum distance the tract extends beyond the inner region in all directions.

wcs : lsst.afw.image.SkyWcs

WCS for tract. The reference pixel will be shifted as required so that the lower left-hand pixel (index 0,0) has pixel position 0.0, 0.0.

Notes

The tract is subdivided into rectangular patches. Each patch has the following properties:

  • An inner region defined by an inner bounding box. The inner regions of the patches exactly tile the tract, and all inner regions have the same dimensions. The tract is made larger as required to make this work.

  • An outer region defined by an outer bounding box. The outer region extends beyond the inner region by patchBorder pixels in all directions, except there is no border at the edges of the tract. Thus patches overlap each other but never extend off the tract. If you do not want any overlap between adjacent patches then set patchBorder to 0.

  • An index that consists of a pair of integers:

    • 0 <= x index < numPatches[0]
    • 0 <= y index < numPatches[1]

    Patch 0,0 is at the minimum corner of the tract bounding box.

  • It is not enforced that ctrCoord is the center of vertexCoordList, but SkyMap relies on it.

Methods Summary

contains(coord) Does this tract contain the coordinate?
findPatch(coord) Find the patch containing the specified coord.
findPatchList(coordList) Find patches containing the specified list of coords.
getBBox() Get bounding box of tract (as an afwGeom.Box2I)
getCtrCoord() Get ICRS sky coordinate of center of tract (as an lsst.geom.SpherePoint)
getId() Get ID of tract
getInnerSkyPolygon() Get inner on-sky region as a sphgeom.ConvexPolygon.
getNumPatches() Get the number of patches in x, y.
getOuterSkyPolygon() Get outer on-sky region as a sphgeom.ConvexPolygon
getPatchBorder()
getPatchIndexPair(sequentialIndex)
getPatchInfo(index) Return information for the specified patch.
getPatchInnerDimensions() Get dimensions of inner region of the patches (all are the same)
getSequentialPatchIndex(patchInfo) Return a single integer that uniquely identifies the given patch within this tract.
getTractOverlap() Get minimum overlap of adjacent sky tracts.
getVertexList() Get list of ICRS sky coordinates of vertices that define the boundary of the inner region.
getWcs() Get WCS of tract.

Methods Documentation

contains(coord)

Does this tract contain the coordinate?

findPatch(coord)

Find the patch containing the specified coord.

Parameters:
coord : lsst.geom.SpherePoint

ICRS sky coordinate to search for.
Returns:
result : lsst.skymap.PatchInfo

PatchInfo of patch whose inner bbox contains the specified coord
Raises:
LookupError

If coord is not in tract or we cannot determine the pixel coordinate (which likely means the coord is off the tract).
findPatchList(coordList)

Find patches containing the specified list of coords.

Parameters:
coordList : list of lsst.geom.SpherePoint

ICRS sky coordinates to search for.
Returns:
result : list of lsst.skymap.PatchInfo

List of PatchInfo for patches that contain, or may contain, the specified region. The list will be empty if there is no overlap.

Notes

Warning:

  • This may give incorrect answers on regions that are larger than a tract.
  • This uses a naive algorithm that may find some patches that do not overlap the region (especially if the region is not a rectangle aligned along patch x,y).
getBBox()

Get bounding box of tract (as an afwGeom.Box2I)

getCtrCoord()

Get ICRS sky coordinate of center of tract (as an lsst.geom.SpherePoint)

getId()

Get ID of tract

getInnerSkyPolygon()

Get inner on-sky region as a sphgeom.ConvexPolygon.

getNumPatches()

Get the number of patches in x, y.

Returns:
result : tuple of int

The number of patches in x, y
getOuterSkyPolygon()

Get outer on-sky region as a sphgeom.ConvexPolygon

getPatchBorder()
getPatchIndexPair(sequentialIndex)
getPatchInfo(index)

Return information for the specified patch.

Parameters:
index : tuple of int

Index of patch, as a pair of ints; or a sequential index as returned by getSequentialPatchIndex; negative values are not supported.
Returns:
result : lsst.skymap.PatchInfo

The patch info for that index.
Raises:
IndexError

If index is out of range.
getPatchInnerDimensions()

Get dimensions of inner region of the patches (all are the same)

getSequentialPatchIndex(patchInfo)

Return a single integer that uniquely identifies the given patch within this tract.

getTractOverlap()

Get minimum overlap of adjacent sky tracts.

getVertexList()

Get list of ICRS sky coordinates of vertices that define the boundary of the inner region.

Notes

warning: this is not a deep copy.

getWcs()

Get WCS of tract.

Returns:
wcs : lsst.afw.geom.SkyWcs

The WCS of this tract