Appendix A: Data Descriptor Record

The contents of the main DDR, which applies to the entire image, are listed first, followed by the contents of the BDR, which give band-specific data for each band. Refer to the LAS Programmer's Guide for the manner in which each LAS module updates the DDR.

DDR Integer Fields

nl		Number of lines in image
ns		Number of samples in image
nbands		Number of bands in image
dtype		Data type of samples 1 unsigned char 2 short 3 long 4 float
master_line		Line relative to master image
master_sample		Sample relative to master image
valid[0]		=> projection code valid flag		NOTE: Flag values are 0 INVALID 1 VALID 2 UNKNOWN
valid[1]		=> zone code valid flag
valid[2]		=> datum code valid flag
valid[3]		=> projection coefficients valid flag
valid[4]		=> ground units valid flag
valid[5]		=> ground distance valid flag
valid[6]		=> corner coordinates valid flag
valid[7]		=> line/sample increments valid flag
proj_code		GCTP projection code
zone_code		UTM or State Plane zone
datum_code		Code for the datum/ellipsoid; Represents ellipsoid ONLY if less than 100

DDR Character String Fields

system[12]		Computer system used to create data
proj_units[12]		Projection units (GCTP units or user defined)
last_used_date[12]		Last access date		NOTE: All ddr dates are stored as "dd-mmm-yy". For example, a date of December 31, 1986 is stored as: "31-dec-86" with month in lower case.
last_used_time[12]		Last access time.		NOTE: All ddr times are stored using a twenty-four hour clock. Seconds are separated by a colon. Example: 1:05:55 pm is stored as 1305:55.

DDR Double Precision Fields

proj_coef[15]		Projection parameters; refer to GCTP documentation for field definitions
upleft[2]		Upper left corner		NOTE: Coordinates are for the center of the corner pixel. Values may be (latitude,longitude) or projection (y,x) coordinates; i.e., northing and easting.
loleft[2]		Lower left corner
upright[2]		Upper right corner
loright[2]		Lower right corner
pdist_y		Projection distance per pixel, y-direction
pdist_x		Projection distance per pixel, x-direction
line_inc		Line increment for sampling		NOTE: The line/sample increments are the values applied to the original image to obtain this image. If resampling or subsampling was not applied, the value contained in these fields is 1.0.
sample_inc		Sample increment for sampling

BDR Double Precision Fields

minval		Minimum pixel value
maxval		Maximum pixel value

BDR Character String Fields

bandno		Band number
valid		Validity flag for min/max 0 INVALID 1 VALID 2 BOUNDED
source[32]		Source of data
instrument[32]		Type of sensor (remotely sensed imagery) or variable (other data)
direction[64]		Direction of the capture process (satellite imagery) or description (other data)
date[10]		Capture date (remotely sensed imagery) or data release date; same format as last_used_date
time[10]		Capture time (remotely sensed imagery) or data release time; same format as last_used_time