PRO region_overlap_2d, r1xlo, r1xhi, r1ylo, r1yhi, r2xlo, r2xhi, r2ylo, r2yhi, oxlo, oxhi, oylo, oyhi, status

; Description: This module determines the overlap region between two rectangular regions in two dimensions. 
;              The first region is defined by "[r1xlo:r1xhi,r1ylo:r1yhi]" and the second region is 
;              defined by "[r2xlo:r2xhi,r2ylo:r2yhi]". The overlap region is defined by
;              "[oxlo:oxhi,oylo:oyhi]". If the overlap region is non-empty then "status" is returned with
;              the value "1", otherwise "status" is returned with the value "0".
;
; Input Parameters:
;
;   r1xlo - INTEGER/LONG - The x index/pixel number of the bottom left hand corner of the first region.
;   r1xhi - INTEGER/LONG - The x index/pixel number of the top right hand corner of the first region. This  
;                          parameter must have a value that is greater than or equal to the value of the
;                          parameter "r1xlo".
;   r1ylo - INTEGER/LONG - The y index/pixel number of the bottom left hand corner of the first region.
;   r1yhi - INTEGER/LONG - The y index/pixel number of the top right hand corner of the first region. This
;                          parameter must have a value that is greater than or equal to the value of the 
;                          parameter "r1ylo".
;   r2xlo - INTEGER/LONG - The x index/pixel number of the bottom left hand corner of the second region.
;   r2xhi - INTEGER/LONG - The x index/pixel number of the top right hand corner of the second region. This
;                          parameter must have a value that is greater than or equal to the value of the 
;                          parameter "r2xlo".
;   r2ylo - INTEGER/LONG - The y index/pixel number of the bottom left hand corner of the second region.
;   r2yhi - INTEGER/LONG - The y index/pixel number of the top right hand corner of the second region. This
;                          parameter must have a value that is greater than or equal to the value of the 
;                          parameter "r2ylo".
;
; Output Parameters:
;
;   oxlo - LONG - The x index/pixel number of the bottom left hand corner of the overlap region. This
;                 parameter is returned with a value of "0" if the overlap region is empty.
;   oxhi - LONG - The x index/pixel number of the top right hand corner of the overlap region. This
;                 parameter is returned with a value of "0" if the overlap region is empty.
;   oylo - LONG - The y index/pixel number of the bottom left hand corner of the overlap region. This
;                 parameter is returned with a value of "0" if the overlap region is empty.
;   oyhi - LONG - The y index/pixel number of the top right hand corner of the overlap region. This
;                 parameter is returned with a value of "0" if the overlap region is empty.
;   status - INTEGER - This parameter is returned with a value of "1" if the overlap region is non-empty,
;                      and it is returned with a value of "0" if the overlap region is empty.
;
; Author: Dan Bramich (dan.bramich@hotmail.co.uk)
;
; History:
;
;   18/08/2008 - Module created (dmb)

;Check that the input parameters are numbers of the correct type

;Calculate the size of each region

;If the sizes of either region are not sensible, then return with an empty overlap region

;Determine the overlap region

;If an overlap region exists, then set the value of "status" to "1"

;If there is no overlap region, then set the value of "status" to "0" and return an empty overlap region