Image Calibrations
I've been given an SPC directory, how do I know which calibrations have been performed?
Radiometric Calibration
SPC normally uses images that have no radiometric calibration, so the image pixel values will be DN and not I/F. However, the easiest way to check is to use the USGS ISIS tool raw2isis on the DAT in the IMAGEFILES directory. To use raw2isis, you need to know the number of bits in the image (i.e. 8-bit or 16-bit), the endianness [i.e. big-endian (BE or LSB) or little-endian (LE or MSB)], and the pixel/line number (usually 512x512 or 1024x1024 for a framing camera). If the values of each pixel are multiples of 2 then the image values are in DN, if the values are floats then it is likely I/F and the image has been radiometrically calibrated.
Geometric Distortion
Geometric distortion can enter in two ways.
One is in INIT_LITHOS.TXT via the DISTORT entry. Examples are below
DISTORT= 'M#########F1' 'OPENCV' 8 0.00177 9.1096e-01 -1.4480e+01 -1.7173e-02 0 0 0 -4.2536e-03 1.1334e-03 DISTORT= 'M#########F2' 'OPENCV' 8 -0.00051 9.1096e-01 -1.4480e+01 -1.7173e-02 0 0 0 -4.2536e-03 1.1334e-03 DISTORT= 'M#########F3' 'OPENCV' 8 -0.00067 9.1096e-01 -1.4480e+01 -1.7173e-02 0 0 0 -4.2536e-03 1.1334e-03 DISTORT= 'M#########F4' 'OPENCV' 8
The other is in the SUMFILE and will be on the line labeled DISTORTION. If the values are non-zero (like in the example below) there is a geometric distortion being applied. If the values are all zero, then there is no geometric distortion entering from the SUMFILE.
N1465662270
2004 JUN 11 16:00:20.254
512 512 145 4095 NPX, NLN, THRSH
0.2002703000D+04 0.2565000000D+03 0.2565000000D+03 MMFL, CTR
0.4287030303D+02 -0.7901427206D+05 0.1919172534D+05 SCOBJ
-0.2909591359D+00 0.2257655554D+00 0.9297164596D+00 CX
-0.9567353433D+00 -0.6918101315D-01 -0.2826154105D+00 CY
0.5139015058D-03 -0.9717221318D+00 0.2361267339D+00 CZ
-0.9538825149D+00 0.2782154063D-02 -0.3001672989D+00 SZ
41.66665 0.00000 0.00000 0.00000 41.67140 0.00000 K-MATRIX
0.00000D+00 0.82800D-05 0.54500D-05 -0.19670D-04 DISTORTION
0.9999999999D-03 0.1000000000D-02 0.9999999999D-03 SIGMA_VSO
0.9718177852D-06 0.1041168580D-05 0.8622155975D-03 SIGMA_PTG
Flat Fielding
Dark Current