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AST_SPHMAP
Create a SphMap
Description:
This function creates a new
SphMap and
optionally initialises its attributes.
A SphMap is a Mapping which transforms points from a 3-dimensional Cartesian coordinate
system into a 2-dimensional spherical coordinate system (longitude and latitude on a unit
sphere centred at the origin). It works by regarding the input coordinates as position vectors
and finding their intersection with the sphere surface. The inverse transformation always
produces points which are a unit distance from the origin (i.e. unit vectors).
Invocation
RESULT = AST_SPHMAP( OPTIONS, STATUS )
Arguments
OPTIONS = CHARACTER
(
)
(Given)
A character string containing an optional comma-separated list of attribute assignments
to be used for initialising the new SphMap. The syntax used is identical to that for the
AST_SET routine.
STATUS = INTEGER (Given and Returned)
The global status.
Returned Value
AST_SPHMAP = INTEGER
A pointer to the new SphMap.
Notes:
-
The spherical coordinates are longitude (positive anti-clockwise looking from the positive latitude
pole) and latitude. The Cartesian coordinates are right-handed, with the x axis (axis 1) at zero
longitude and latitude, and the z axis (axis 3) at the positive latitude pole.
-
At either pole, the longitude is set to the value of the PolarLong attribute.
-
If the Cartesian coordinates are all zero, then the longitude and latitude are set to the value
AST__BAD.
-
A null Object pointer (AST__NULL) will be returned if this function is invoked with STATUS set
to an error value, or if it should fail for any reason.
Status Handling
The protected
interface to this function includes an extra parameter at the end of the parameter list
descirbed above. This parameter is a pointer to the integer inherited status variable: " int
status" .
Status Handling
The protected interface to this function includes an extra parameter at the end of the
parameter list descirbed above. This parameter is a pointer to the integer inherited status variable: " int
status" .
Status Handling
The protected interface to this function includes an extra parameter at the end of the
parameter list descirbed above. This parameter is a pointer to the integer inherited status variable: "
int status" .
Copyright (C) 2021 East Asian Observatory
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A Library for Handling
World Coordinate
Systems
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