Imagecat is the default name given to processed image catalogs. There can be multiple Imagecat files, and these files can reside in any directory. Next to each Imagecat file, there is an Imcatdir directory. This directory contains the reduced images corresponding to Imagecat entries.
The format of this file can be found in the Terascan include file imcat.h in the structure IMCATREC as follows:
#define IMCAT_HIST_LEN 64
typedef struct {
char project[GP_MAX_NAME +1];
char file[GP_MAX_NAME +1];
char varname[GP_MAX_NAME +1];
char units[GP_MAX_NAME +1];
char satel[MAX_SATEL_NAME +1];
int date; /* date, days since 1900/1/1, inclusive */
int time; /* start time of data, seconds of the day */
int nl, ns; /* number of lines, samples in image */
int datatype; /* from gp.h */
int projection; /* projection code from etx.h */
float clat, clon; /* center latitude, longitude in degrees */
float mapangle; /* rotation angle in degrees */
float projparam; /* addition projection parameter in degrees */
float affine[6]; /* etx affine transform */
float lat[4]; /* corner latitude in degrees */
float lon[4]; /* corner longitude in degrees */
float usemin, usemax; /* minimum, maximum values */
int ngood; /* number of non-missing values */
/* in range [ minval, maxval ] */
unsigned char hist[IMCAT_HIST_LEN]; /* fraction * 250 */
int logtime; /* log time; seconds since 70/1/1 */
short status; /* catalog record status; see below */
short checksum; /* sum of all bytes except checksum */
} IMCATREC;
/* catalog record status codes */
#define NORMAL 0
#define DELETED 1
#define DISABLED 2 /* ignore during search */
#define SELECTED 4 /* temporary status, never stored */
GP_MAX_NAME is defined as 31 in the include file gp.h. MAX_SATEL_NAME is defined as 11 in the include file etx.h. For images based on a map projection, clat, clon, imagangle, projparam, and affine fields are used to parameterize the map projection. Note that (clat, clon) is the center of the map projection, not necessarily the center of the image.
Corner (lat,lon) coordinates are computed (or at least estimated) for images with earth location. Estimation is used for images with edges intersecting outer space. Center (clat, clon) are computed for images with earth location in sensor scan (not map projection) coordinates.
For each entry in a given Imagecat file, there is a reduced image stored in the corresponding Imcatdir directory. Reduced images are at most 256 X 256 and are stored as Sunraster files. The name of the reduced image is formed by concatenating the image's project, file, and variable names, separating each name with a comma (e.g., project, file, variable).
Imagecat, Imcatdir
image_catalog, rasterfile, addimcat, delimcat, initimcat, listimcat, packimcat
The user should never write directly to this file and should use the library routines to read this file, if required.
At some point, the reduced images will be compressed using a lossy JPEG compression scheme. Lossy means that some bits are sacrificed for added compression.
Last Update: $Date: 1999/05/10 20:58:55 $