B.1.7 Coverage

Functions related to coverage and footprints.

One coverage standard is Multi-Order Coverage maps, described at http://www.ivoa.net/Documents/MOC/. MOC positions are always defined in ICRS equatorial coordinates.

MOCs may be specified using a string argument of the functions in one of the following ways:

• The filename of a MOC FITS file
• The URL of a MOC FITS file
• The identifier of a VizieR table, for instance "V/139/sdss9" (SDSS DR9)
• An ASCII MOC string, for instance "1/1 2 4 2/12-14 21 23 25 8/"

A list of all the MOCs available from VizieR can currently be found at https://alasky.cds.unistra.fr/footprints/tables/vizier/. You can search for VizieR table identifiers from the VizieR web page (https://vizier.cds.unistra.fr/); note you must use the table identifier (like "V/139/sdss9") and not the catalogue identifier (like "V/139").

inMoc( moc, ra, dec )

Indicates whether a given sky position falls strictly within a given MOC (Multi-Order Coverage map). If the given moc value does not represent a MOC (for instance no file exists or the file/string is not in MOC format) a warning will be issued the first time it's referenced, and the result will be false.

• Parameters:
  • moc (String): a MOC identifier; a filename, a URL, a VizieR table name, or an ASCII MOC string
  • ra (floating point): ICRS right ascension in degrees
  • dec (floating point): ICRS declination in degrees
• Return value
  • (boolean): true iff the given position falls within the given MOC

nearMoc( moc, ra, dec, distanceDeg )

Indicates whether a given sky position either falls within, or is within a certain distance of the edge of, a given MOC (Multi-Order Coverage map). If the given moc value does not represent a MOC (for instance no file exists or the file/string is not in MOC format) a warning will be issued the first time it's referenced, and the result will be false.

• Parameters:
  • moc (String): a MOC identifier; a filename, a URL, a VizieR table name, or an ASCII MOC string
  • ra (floating point): ICRS right ascension in degrees
  • dec (floating point): ICRS declination in degrees
  • distanceDeg (floating point): permitted distance from MOC boundary in degrees
• Return value
  • (boolean): true iff the given position is within distance degrees of the given MOC

mocSkyProportion( moc )

Returns the proportion of the sky covered by a given MOC.

If the given moc value does not represent a MOC (for instance no file exists or the file/string is not in MOC format) a warning will be issued the first time it's referenced, and the result will be NaN.

• Parameters:
  • moc (String): a MOC identifier; a filename, a URL, a VizieR table name, or an ASCII MOC string
• Return value
  • (floating point): a fractional value in the range 0..1

mocTileCount( moc )

Returns the number of unique tiles within a given MOC.

If the given moc value does not represent a MOC (for instance no file exists or the file/string is not in MOC format) a warning will be issued the first time it's referenced, and the result will be 0.

• Parameters:
  • moc (String): a MOC identifier; a filename, a URL, a VizieR table name, or an ASCII MOC string
• Return value
  • (long integer): number of tiles in the MOC

mocUniq( order, index )

Converts a HEALPix order and and tile index into a UNIQ-encoded integer as used in MOC encoding. The result is index + 4**(1+order).

If the order or index are out of bounds, behaviour is undefined.

• Parameters:
  • order (integer): HEALPix order, in range 0..29
  • index (long integer): tile index within the given level
• Return value
  • (long integer): uniq-encoded value

uniqToOrder( uniq )

Extracts the HEALPix order from a UNIQ-encoded integer as used in MOC encoding.

If the supplied value is not a legal UNIQ integer, -1 is returned.

• Parameters:
  • uniq (long integer): uniq-encoded value
• Return value
  • (integer): HEALPix order

uniqToIndex( uniq )

Extracts the HEALPix pixel index from a UNIQ-encoded integer as used in MOC encoding.

If the supplied value is not a legal UNIQ integer, -1 is returned.

• Parameters:
  • uniq (long integer): uniq-encoded value
• Return value
  • (long integer): pixel index

indicesToMocAscii( order, indices )

Converts a list of HEALPix indices at the same order into a MOC, and returns its ASCII representation.

Note this may not be a very fast operation, so use within TOPCAT, where evaluation is lazy and happens every time the cell value is required, may lead to slow behaviour.

• Parameters:
  • order (integer): MOC order of tiles
  • indices (array of long integer): array of tile indices at the given order
• Return value
  • (String): ASCII representation of MOC at the given order
• Example:
  • indicesToMocAscii(1,intArray(24,25,26,27,39,42,43)) = "0/6 1/39 42-43"

SPHERE_STERADIAN

The number of steradians on the sphere, 4 PI.

SPHERE_SQDEG

The number of square degrees on the sphere, approx 41253.