To read data from an image array, the calling program must contain the following function calls:
C: ri_id = GRselect(gr_id, ri_index);
status = GRreadimage(ri_id, start, stride, edges, data);
status = GRendaccess(ri_id);
FORTRAN: ri_id = mgselct(gr_id, ri_index)
status = mgrdimg(ri_id, start, stride, edges, data)
OR status = mgrcimg(ri_id, start, stride, edges, data)
status = mgendac(gr_id)
GRreadimage can be used to read either an entire image or a subsample of the image. The ri_id argument is the raster image identifier returned by GRselect. As with GRwriteimage, the arguments start, stride, and edges respectively describe the starting location for the read operation, the number of locations the current image array location will be moved forward after each read, and the length of each dimension to be read. Refer to Section 8.6.1 on page 265 for detailed descriptions of the parameters start, stride, and edges. If the image array is smaller than the data argument array, the amount of data read will be limited to the maximum size of the image array.
Note that the FORTRAN-77 version of GRreadimage has two routines; mgrdimg reads numeric image data and mgrcimg reads character image data.
SUCCEED (or 0) or FAIL (or -1). The parameters for GRreadimage are further defined in (See Table 8F.).
8.7.2 Setting the Interlace Mode for an Image Read: GRreqimageil
The GRreqimageil routine sets the interlace mode for the next image read. The syntax of this routine is as follows:C: status = GRreqimageil(ri_id, interlace_mode);
FORTRAN: status = mgrimil(ri_id, interlace_mode)
GRreqimageil can be called at any time before the read operation and takes two parameters, ri_id and interlace_mode. The parameter ri_id is the raster image identifier returned by the GRselect routine and the parameter interlace_mode specifies the interlace mode that will be in effect for the image read operation. Refer to Section 8.5.1 on page 264 for a description of the GR interlace modes.
GRreqimagetil may be called more than once; the interlace mode setting specified by the last call to the routine will be used for the next read operation.
SUCCEED (or 0) or FAIL (or -1). The parameters of this routine are further defined in Table 8F.
TABLE 8F - GRreadimage and GRreqimageil Parameter Lists
In this example, the program reads the image written by Example 1 and modified by Example 2 in the file "General_RImages.hdf". Recall that this image has two components and has 5 rows and 10 columns. The program first reads the entire image, then reads a subset of the image, 3 rows and 2 columns starting at the 2nd row and the 4th column, and finally reads the image skipping all the even rows and all the odd columns. Reading patterns are applied to all components.
C version