uk.ac.starlink.ttools.plot2.layer

Class SkySurfaceTiler

java.lang.Object

uk.ac.starlink.ttools.plot2.layer.SkySurfaceTiler

public class SkySurfaceTiler
extends Object

Understands the geometry of HEALPix tiles on a given SkySurface.

Note: this class is intended for use when the number of tiles is moderately small. Use of resources (memory, runtime?) is likely to be linear in the number of pixels at the required order appearing within the given surface.

Note: instances of this class are not safe for concurrent use from multiple threads.

Since:

31 Mar 2016

Author:

Mark Taylor

Constructor Summary

Constructors

Constructor and Description
SkySurfaceTiler(SkySurface surf, Rotation rotation, int hpxOrder) Constructor.

Method Summary

Modifier and Type	Method and Description
Polygon	getTileShape(long hpxIndex) Returns the shape of the given tile on the sky surface.
boolean	isVisible(long hpxIndex) Indicates whether a given tile is considered to be visible on this tiler's plot surface.
Set<Long>	visiblePixels() Returns a collection of pixels that are, or may be, visible on the surface.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SkySurfaceTiler

public SkySurfaceTiler(SkySurface surf,
                       Rotation rotation,
                       int hpxOrder)

Constructor.

Parameters:

surf - sky surface

rotation - additional rotation to apply to sky positions, not null

hpxOrder - healpix order (0, 1, 2, ..)

Method Detail

visiblePixels

public Set<Long> visiblePixels()

Returns a collection of pixels that are, or may be, visible on the surface. It may contain false positives, but an attempt is made to keep that number low. Calling this method is cheap (the same object is returned every time), and iterating over the result is a sensible way to find all the visible pixels.

Returns:

an unmodifiable set of HEALPix indices for pixesl that are, or may be visible on the surface.

isVisible

public boolean isVisible(long hpxIndex)

Indicates whether a given tile is considered to be visible on this tiler's plot surface. False positives are permitted (but preferably not too many). This should be faster to execute than getTileShape(long).

Parameters:

hpxIndex - HEALPix index

Returns:

true iff tile may be visible

getTileShape

public Polygon getTileShape(long hpxIndex)

Returns the shape of the given tile on the sky surface. The result is an approximation using integer graphics coordinates.

Calling this method is not an efficient way to determine whether a given pixel is visible; use isVisible instead.

Parameters:

hpxIndex - HEALPix index

Returns:

shape of indicated tile on graphics plane, or null if known to be invisible