register

(Compiled by DL)

Purpose: Program for registering (adding and aligning) new images to existing maplets.

Register cross-correlates an image with existing data to update the knowledge of the spacecraft position/attitude. Register is limited to 2 degrees of freedom.

Requires

• IMAGEFILES/ - a directory containing the image .DAT files;

• NOMINALS/ - a directory containing the image .NOM files (starting solution image, S/C and camera information);

• SUMFILES/ - a directory containing the image .SUM files (updated solution image, S/C and camera information; lmrks and limbs);

• MAPFILES/ - required for comparison with a reference map;

• SHAPEFILES/ - required for comparison with a shape model.

Optional

• make_scriptR.seed - for batch processing using make_scriptR.

Output

• NOMINALS/ - If the user selects the option to update the NOMINAL file, starting S/C and camera information will be updated (an option not typically selected);

• SUMFILES/ - S/C and camera information are updated as image shifts are made. The user can discard these changes upon quit;

• TEMPFILE.pgm - A side by side view of the image (left) and the reference (right);
• TEMPFILE.ppm - A red/cyan composite of the two items (red is image, cyan is reference).

Using register

(The following section is taken from SPOC v3.02A PDF/LITHOSPHERE/REGISTER.f File Reference, rearranged for convenience.)

REGISTER provides an initial estimate for the spacecraft state (camera pointing and s/c-object vector) by aligning an image with a known object - either the shape model, a high resolution map or another (already registered) image.

Input stdin

 input 12-character picture name. q to quit.

The user enters the image name as stored in IMAGEFILES. Some versions of process_fits will make some changes to the filename, so it may not be the "original" name.

 s = shape
 i = reference image
 m = reference map

The user enters the object to align with.

• s = shape - to use the current shape model;
• i = image - select an already registered image; user will be prompted for an image name;

• m = map - use a maplet/bigmap; user will be prompted for a map name. If 0 is chosen for the map name, the program will search a set of "Zmaps" for the one most likely to overlap the image. Maps are only used after a detailed shape model and high-resolution maps have been constructed. At that time we are registering new images for navigation or improving the topography.

 enter scale (km/px)

A final entry is the scale in km. The basic display for REGISTER is 600x600 pixels. If the body in question is, say 500 m across, then if the scale is chosen to be 5 m (.005) the image will be 100 pixels across in the display.

Output

 gc TEMPFILE.pgm
 gc TEMPFILE.ppm

• TEMPFILE.pgm - A side by side view of the new image (left) and the reference (right);
• TEMPFILE.ppm - A red/cyan composite of the two items (new is red, cyan is reference).

Example TEMPFILE.pgm:

Example TEMPFILE.ppm:

The display and the arrays of image and reference data are not the actual imaging data, but that data projected on a "substrate". When we are just starting processing and looking at low-resolution images of the body, the substrate is simply a plane through the body center oriented parallel to the camera's focal plane. This flat 'f' substrate is the default value. Once a decent shape model is obtained and our images cover a small fraction of the body's surface, the substrate is taken to be that surface itself, either in the form of the shape 's' or a high-resolution map 'm'. In this case, the topography is represented as a DTM whose reference plane is the same as the flat substrate with heights in the negative camera bore sight direction. Note that if the reference is also an image, this data is projected on the same substrate as the image being registered.

The main menu looks like:

 0. Quit
 1. Change scale
 2. Global shift
 3. Shift unknown (LEFT/RED) image
 4. Rotate unknown (LEFT/RED) image
 5. Change reference
 6. Change RANGE of (LEFT/RED) image
 7. Revert to nominal
 8. Change substrate 
 9. Update nominal and quit
 a. Toggle bkg
 b. Toggle image for Vlm
 c. Change correlation limit
 d. Fix/Unfix scobj
 e. Fix/Unfix pointing
 t. Tuck picture

Options 1, 5 and 8 allow you to change the scale, reference object and substrate, respectively.

Option 2: Sometimes when we are trying to align an image to a reference, the entire display is off center. The '2' option moves both the image and reference displays by the same amount so that we can more conveniently align them, usually at smaller scale. This option only changes the user's point of view, not the image's location.

Options 3, 4 and 6 make changes to the .SUM file in camera pointing and/or cross line-of sight scobj, camera twist and s/c range, respectively.

Option 3 is the option most used. The new image is on the left or in red. Values entered (delta x, delta y) are the number of pixels by which the image will be shifted (as per the current scale). Note, this isn't moving the "window" like in lithos, but updating the image's camera position and pointing. The program first asks whether an autocorrelate should be attempted:

 Autocorrelate? (y/n)
y
        0.00000        0.00000        0.27302
 Enter px/ln IMAGE shift

Autocorrelate estimates the offset between the image and the reference. The three values displayed in standard out are the delta x (pixels), delta y (lines), and the correlation score. If the correlation gives a good match (greater than a preset limit, default=0.25), autocorrelate will shift the image and go back to the menu. Otherwise autocorrelate will ask for a manual input. The preset limit can be changed with option c.

Option 7 populates the working .SUM file. Thie is sometimes a baleout procedure after having screwed up the .SUM file in some way. However, we have now introduced a new option 9 that lets us save the current result as the nominal without changing the .SUM file from its original value. If for example, the spacecraft range is out to lunch (as it was on Hayabusa) the working .SUM file can be populated with the nominal, a change made to the range with option 6, and the new nominal saved with option 9.

Option a: When we are correlating small images to a nominal shape, we want to use all the data, so the space off the body counts just as much as the body itself. The procedure wakes up with a "background" turned on so that this correlation can be performed. By typing 'a', we toggle this background off, so it is only the common topography that is correlated between the image and the reference object.

Option b allows a flag to be set on the image that will enable its brightness variations to be used to determine topography but keeps it from participating in the geometry solution for the landmark vector. This is used to keep Mariner 10 images of Mercury, which have questionable nominals, from messing up the vector but still, with their sometimes unique sun angles, helping with the topography determination.

Option c allows the user to change the autocorrelation limit (default=0.25).

Options d and e: When an image shift has been determined, either manually or through autocorrelation, The camera pointing and spacecraft-object (scobj) vector in the .SUM file are changed in a manner weighted by their respective sigmas in the nominals (.NOM) file. If we want to keep one or the other unchanged, we use the 'd' or 'e' option to fix it.

Option t allows an image to be tucked so it will not participate in the SPC process at all. It could be tucked from LITHOS, but it often happens that as REGISTER is used to cycle through new images, problems are easily seen and dealt with immediately.

0. Quit: This gives the user the chance to save or discard changes, and then register the next image. All toggle options will persist until the user quits register.

 Accept shift? (y/n)
 Update/Create rotation history file? (y/n)
 Update nominal file? (y/n)

Accept shift?: Note that the shift has already been applied (the SUMFILE is updated in real time), in order to undo all changes since the last quit, the user must select 'n'.

Update/Create rotation history file?: Always 'n'. The rotation history file was introduced to keep track of pointing errors in Clementine data during Lunar orbits in an attempt to quantify systematic shifts.

Update nominal file?: Usually 'n'. It is rare that we want to set the nominal file equal to the .SUM solution.

User Warning

Since the SUMFILE is updated in realtime, an uncontrolled exit from register will result in the SUMFILE remaining modified.

Examples

 ~/bin/register 

 input 12-character picture name. q to quit.
N110751047R

REFERENCE MAP = ZS0426

 Input reference
 s. SHAPE
 i. IMAGE
 m. MAP
m
 Input REFNM
TSI003
 enter scale (km/px)
.6118483

 0. Quit
 1. Change scale
 2. Global shift
 3. Shift unknown (LEFT/RED) image
 4. Rotate unknown (LEFT/RED) image
 5. Change reference
 6. Change RANGE of (LEFT/RED) image
 7. Revert to nominal
 8. Change substrate (s)
 9. Change pole
 a. Turn off bkg
 b. Turn off image for Vlm
 c. Change correlation limit =   0.25
 d. Fix scobj
 e. Fix pointing
 t. Tuck picture
 Current picture   = N110751047R 
 Current reference = TSI003      

Registering an image with a shape:

Registering an image with a bigmap:

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