ManglePolygon

class pydl.pydlutils.mangle.ManglePolygon(*args, **kwargs)

Bases: object

Simple object to represent a polygon.

A polygon may be instantiated with a row (FITS_record) from a FITS_polygon object, another ManglePolygon object (copy constructor), keyword arguments, or with no arguments at all, in which case it represents the whole sky.

Attributes:

cm : ndarray

The size of each cap in the polygon.

id : int

An arbitrary ID number.

pixel : int

Pixel this polygon is in.

use_caps : int

Bitmask indicating which caps to use.

weight : float

Weight factor assigned to the polygon.

Attributes Summary

ncaps	Number of caps in the polygon.
str	Solid angle of this polygon (steradians).
x	The orientation of each cap in the polygon.

Methods Summary

add_caps(x, cm)	Create a new polygon that contains additional caps.
cmminf()	The index of the smallest cap in the polygon, accounting for negative caps and use_caps.
copy()	Return an exact copy of the polygon.
garea()	Compute the area of a polygon.
gzeroar()	If at least one cap has zero area, then the whole polygon has zero area.
polyn(other, n[, complement])	Intersection of a polygon with the n th cap of another polygon.

Attributes Documentation

ncaps

Number of caps in the polygon.

str

Solid angle of this polygon (steradians).

x

The orientation of each cap in the polygon. The direction is specified by a unit 3-vector.

Methods Documentation

add_caps(x, cm)

Create a new polygon that contains additional caps. The caps are appended to the existing polygon’s caps.

Parameters:

x : ndarray or recarray

X values of the new caps.

cm : ndarray or recarray

CM values of the new caps.

Returns:

:class:`ManglePolygon`

A new polygon object.

cmminf()

The index of the smallest cap in the polygon, accounting for negative caps and use_caps.

Returns:

:class:`int`

Integer index of the smallest cap.

copy()

Return an exact copy of the polygon.

Returns:

:class:`ManglePolygon`

A new polygon object.

garea()

Compute the area of a polygon.

See [1] for the detailed area formula, which is summarized here:

• An empty polygon with no caps is defined to be the whole sky.
• A polygon with one cap has area 2*pi*self.cm.
• A polygon with at least one cap with an area less than \(2\pi\) has an area less than \(2\pi\).
• If every cap has an area greater than \(2\pi\), split the polygon into two smaller polygons and sum the two areas.

Returns:

:class:`float`

The area of the polygon.

References

[1]	Hamilton, A. J. S.; Tegmark, Max, 2004 MNRAS 349, 115.

gzeroar()

If at least one cap has zero area, then the whole polygon has zero area.

Returns:

:class:`bool`

True if the area is zero.

polyn(other, n, complement=False)

Intersection of a polygon with the n th cap of another polygon.

Parameters:

other : ManglePolygon

Polygon containing a cap to intersect the first polygon with.

n : int

Index of the cap in other.

complement : bool, optional

If True, set the sign of the cm value of other to be the complement of the original value.

Returns:

:class:`~pydl.pydlutils.mangle.ManglePolygon`

A polygon containing the intersected caps.