Help for PHOTLIST

PURPOSE:

PHOTLIST will compute the photometric parameters for specified areas of
an image.  PHOTLIST is restricted to Voyager images.

EXECUTION:

    PHOTLIST FDS=1636832 SCET=(1979,63,19,23,0,0) TARGET=IO         CRAFT=VGR-1 CAMERA=ISSN
where

    FDS is the 7-digit Flight Data System counter (FDS) specified as
       xxxxxyy where xxxxx is the Mod16 count and yy is the Mod60 count.
    SCET is the spacecraft event time specified as (year,day,hr,min,sec,msce).
    TARGET is the name of the target body.
    CRAFT is either VGR-1 or VGR-2.
    CAMERA is either ISSN or ISSW for the narrow and wide angle cameras.

OPERATION:

PHOTLIST will extract the geometry data for the image from SPICE kernels
and computes the following lighting parameters for the center
(C), upper left (UL), upper right (UR), lower left (LL), and lower right (LR)
corners of the image, and at the target center (OSPC).  The line-sample 
coordinates at the target center is also reported for both geometrically
corrected (object space) and uncorrected (image space) images.  Object space
images have a 1000x1000 format and image space images have an 800x800 format.

SCLK=xxxxxyy
S/C=VGRx  Target=xxxxxxxxxxxx  Radii=(xxxxx.xx, xxxxx.xx)
S/C-Central Body Range=nnnnnnnnn.nn
S/C-Target Body Range=nnnnnnnnn.nn  Lat=nnn.nn  Lon=nnn.nn
Solar Range=nnnnnnnnn.nn  Lat=nnn.nn  Lon=nnn.nn
Object space coordinates at target center=( nnnnnnn., nnnnnnn.)
Image space coordinates at target center=( nnnnnnn., nnnnnnn.)
                Narrow Angle Camera                   Image Space
    Latitude  Longitude  Phase   Incidence  Emission  Line      Sample
C    nn.nn    nnn.nn     nnn.nn    nnn.nn    nnn.nn   nnn.nnnn  nnn.nnnn
UL   nn.nn    nnn.nn     nnn.nn    nnn.nn    nnn.nn   nnn.nnnn  nnn.nnnn
UR   nn.nn    nnn.nn     nnn.nn    nnn.nn    nnn.nn   nnn.nnnn  nnn.nnnn
LL   nn.nn    nnn.nn     nnn.nn    nnn.nn    nnn.nn   nnn.nnnn  nnn.nnnn
LR   nn.nn    nnn.nn     nnn.nn    nnn.nn    nnn.nn   nnn.nnnn  nnn.nnnn
PC   nn.nn    nnn.nn     nnn.nn    nnn.nn    nnn.nn   nnn.nnnn  nnn.nnnn
 C-matrix source for frame xxxxxxx is FARENC

All longitudes are reported in System 3 west-longitude.  All latitudes are
planetocentric.

All calculations assume an oblate spheroid target model.  The equatorial and
polar radii are printed beside the target name.

The C matrix source is an indication of how accurately the camera pointing is
known.  If the source is SEDR, then the source of the camera pointing is from
predict data, and will in general be off by 50 or more pixels.  If the source
is NAV or FARENC, then the camera pointing has been determined by fitting the
limb, and is accurate to within 0.5 pixels or better.  If the source is NAV2,
NEAR, or AMOS, then the camera pointing has been determined via tiepoint
navigation (and is of indeterminate accuracy).  If the source is DAVI, then
the camera pointing has been determined by Mert Davies, and is considered to
be the most reliable source.

POINT OFF TARGET:

The standard image space line-sample coordinates for the center and corners
(called reticle points) of the image are:

             UL=(1,1)                     UR=(1,800)

                          C=(400,400)

             LL=(800,1)                   LR=(800,800)

Occasionally, one or more of the reticle points calculated will be determined
to be off the target.  These points can be replaced by supplying different image
space line-sample coordinates as in the following example:

   photlist 2061657 LL=(500,100) LR=(500,800)

NOTE: By default, the supplied coordinates for C, UL, UR, LL, and LR are in 
      line-sample coordinates; however, such can be overridden by the 'LATLON 
      keyword.

CORRECTING THE CAMERA POINTING:

The camera pointing can be corrected by specifying the object space line-sample
coordinates of the target-center via the OSPC parameter:

   photlist fds=2061657 scet=(1996,232,23,2,35,0) craft=vgr-1       target=jupiter OSPC=(216,-14)

NOTE: the two examples will and should create different result.

For images containing a significant portion of the limb, these coordinates may
be derived via program NAV or measured directly off a print of the raw image.

GEOMETRIC DISTORTIONS:

If the IBIS Reseau file is given (with the RES parameter) the program will read
the reseau locations from that file.  If the parameter is not given the nominal
locations of the reseau marks are used to model the geometric distortion in the
image.  


WARNING: The nominal reseau locations lead to an error of one or two pixels 
         near the center of the image.  The error grows progressively larger 
         toward the image margins and corners.

The distortion is removed by converting the line sample coordinates for each
reticle from the raw (image space) image to (distortion free) object space.

A NOTE ON THE VOYAGER FDS:

The FDS is used as an index for accessing SEDR data.  The FDS associated with
the image is the FDS at the start of the camera cycle during which an image is
read out.  This is normally the same camera cycle in which the exposure takes
place.

A source of confusion occurs when simultaneous exposures are taken through the
narrow angle and wide angle cameras.  When this occurs, the image is read out
from the narrow angle camera immediately, while read-out of the wide angle
camera is suppressed until the following camera cycle.  The FDS associated
with the wide angle image will consequently not coincide with the camera cycle
during which the exposure took place, but will trail by one or more Mod60
counts, depending of the frame rate (FDS = FDS + frame-rate).

PROGRAM HISTORY:

Original  Programmer:  Gary Yagi, April 12, 1996
Cognizant Programmer:  Gary Yagi
Revisions:
 Sep 14 99  GMY  Modify to use SPICE kernels
 Dec  7 96  SMC  Initialize ILAT to 0 before use                         (DFR)
 Oct  1 96  SMC  Change inertial coordinate system from J2000 to EME50.
                   (vgrspice.f, SYSTEM=1 => SYSTEM=2)
 Sep 26 96  SMC  > Modified CONVISOS calls.                          (FR89818)
                 > Modified the output so Radii's output don't overlap
 Jun 19 96  SMC  Modify output report labeling on line 3 and 4
 Jun 12 96  SMC  Took out the PC parameter in favor of OSPC
 May 31 96  SMC  Added the RES parameter and functionality
 May 20 96  SMC  Added the GRID parameter and functionality
 May 20 96  SMC  Added the OSPC parameter and functionality
 May 03 96  SMC  Added the VALUETYPE parameter and functionality
 Apr 14 96  GMY  Ported to Unix
 Apr 17 96  GMY  Added calculations at target center <443>
 Apr 25 96  GMY  Fix identification of VGR-1 and VGR-2
 Apr 26 96  GMY  Added C, UL, UR, LL, LR parameters
 Apr 27 96  GMY  Added PC parameter