gavo.stc.bboxes module

Computing bboxes for STC geometries.

A bbox coming out of this module is a 4-tuple of (ra0, de0, ra1, de1) in ICRS degrees.

(You’re right, this should be part of the dm classes; but it’s enough messy custom code that I found it nicer to break it out).

class gavo.stc.bboxes.GCSegment(long1, lat1, long2, lat2)

Bases: object

A great circle segment on a sphere. It is assumed that it’s no larger than pi.

Construction is long,lat, long, lat in rad (or use the fromDegrees class method.

Very small (<1e-8 rad, say) segments are not supported. You should probably work in the tangential plane on that kind of scale.

classmethod fromDegrees(long1, lat1, long2, lat2)

getBBs()

returns a sequence of bounding boxes for this great circle segment.

Actually, the sequence contains one box for a segment that does not cross the stitching line, two boxes for those that do.

latForLong(long)

returns the latitude the great circle is on for a given longitude.

Input and output is in rad.

If the pole is part of the great circle, a constant (but fairly meaningless) value is returned.

gavo.stc.bboxes.fromRad(bbox)

gavo.stc.bboxes.getBboxes(ast)

iterates over the bboxes of the areas within ast.

bboxes are (ra0, de0, ra1, de1) in ICRS degrees.

gavo.stc.bboxes.getHeading(long1, lat1, long2, lat2)

returns the initial heading when going from one spherical position to another along a great circle.

Everything is in rad, angle is counted north over east.

gavo.stc.bboxes.getStandardFrame()

gavo.stc.bboxes.joinBboxes(*bboxes)

returns a bounding box encompassing all the the bboxes passed in.

No input bbox must cross the stitching line; they must be normalized, i.e., lower left and upper right corners.