PRO image_grid, sx, sy, imxsize, imysize, regions, nregions, status

; Description: This module determines the set of rectangular image regions "regions" created by partitioning 
;              an image of dimensions "imxsize" by "imysize" pixels using a grid with grid elements of size
;              "sx" by "sy" pixels. The grid is defined such that the origin of the image lies in the bottom 
;              left hand corner of a grid element. The resulting image regions will be of size "sx" by "sy" 
;              pixels where the image fully covers a grid element, and of a size smaller than "sx" by "sy" 
;              pixels where the image fails to fully cover a grid element.
;
; Input Parameters:
;
;   sx - INTEGER/LONG - The grid element size along the x-axis (pix).
;   sy - INTEGER/LONG - The grid element size along the y-axis (pix).
;   imxsize - INTEGER/LONG - The image size along the x-axis (pix).
;   imysize - INTEGER/LONG - The image size along the y-axis (pix).
;
; Output Parameters:
;
;   regions - IDL STRUCTURE - This parameter is an IDL structure with the following tags specifying the 
;                             image regions and their sizes:
;
;                             lx - LONG - The x-axis pixel index of the lower left-hand corner of the
;                                         rectangular image region.
;                             ux - LONG - The x-axis pixel index of the upper right-hand corner of the
;                                         rectangular image region.
;                             ly - LONG - The y-axis pixel index of the lower left-hand corner of the
;                                         rectangular image region.
;                             uy - LONG - The y-axis pixel index of the upper right-hand corner of the
;                                         rectangular image region.
;                             xrsize - LONG - The image region size along the x-axis (pix).
;                             yrsize - LONG - The image region size along the y-axis (pix).
;
;   nregions - LONG - The number of image regions specified by the IDL structure "regions".
;   status - INTEGER - This parameter is returned with a value of "1" if the partitioning of the image was
;                      successful, and it is returned with a value of "0" if the partitioning of the image
;                      was unsuccessful.
;
; Author: Dan Bramich (dmb@ing.iac.es)
;
; History:
;
;   22/12/2008 - Module created (dmb)

;Check the values of "sx", "sy", "imxsize" and "imysize"

;Determine the number of grid elements containing image pixels in each of the x and y directions

;Determine the number of required image regions

;For the special case where the whole image lies within one grid element

;Create the output structure containing the image region specifications

  ;Determine the current region limits and size in the x direction

    ;Determine the current region limits and size in the y direction

    ;Save the current region limits and size in the output structure