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# Find V, Z or PTG

(lithos Main Menu Option V. Find V, Z or PTG)

## Description

This Main Menu option is used to calculate the radius vector of maplets, the spacecraft vector, and the spacecraft pointing.

### Suboptions

When you choose Option V. Find V, Z or PTG from the Main Menu, you will see the following set of Suboptions that use these terms:

• V - radius vector to the maplet
• Z - pixel/line image space locations of the landmark (i.e., the image alignment)
• PTG/SCOBJ - spacecraft pointing and position
• nominal - the "initial" space pointing and position

```Main Menu: Q 0123O IUCRSG NVAMBX DEPL FZH? v
>v

1.  V from Z and pointing
2.  Z from V and pointing
3.  PTG/SCOBJ from Z and V (selected image)
4.  PTG/SCOBJ from Z and V (current images)
5.  PTG/SCOBJ from nominal (selected image)
6.  PTG/SCOBJ from nominal (current images)
7.  RA/DEC/TW (selected image)
q.  Quit```

1. V from Z and pointing - Calculates the radius vector from the image alignment and the spacecraft data.

• This is the most commonly used "v" option.

2. Z from V and pointing - Moves images to the alignment predicted by the radius vector and the spacecraft position/pointing.

3. PTG/SCOBJ from Z and V (selected image) - Determines the spacecraft position and pointing based upon the image alignment and radius vector of the maplet. This option asks you to input a specific image on which to perform this calculation.

• Make sure that you have a stable system before you do this! You can move the spacecraft in the wrong direction if you are not careful!

4. PTG/SCOBJ from Z and V (current images) - Similar to option 3 above, but this option does the calculation for all images added to the landmark.

5. PTG/SCOBJ from nominal (selected image) - Resets the spacecraft position and pointing to the nominal (i.e., the original values determined for the mission). This option resets it for a single image.

6. PTG/SCOBJ from nominal (current images) - Same as option 5 above, but this option resets it for all images associated with the loaded landmark.

7. RA/DEC/TW (selected image) - Determines the inertial space orientation of the body-fixed frame (TIPM) at an image UTC with the experimental subroutine IPL2RDT and writes the orientation as RA, DEC, TWIST.

• Work in progress. This is the wobble program(?) R. Gaskell is developing.

## Common Usage

Most of the time, you will only be using option v1. Howewver, v4 is used after the model is stable to update the s/c information, and v2 can be helpful when images are not aligning properly. v2 can also be used when you suspect there is something wrong with the model. If the model has problems, the v2 option will manifest by wildly moving the image around.

• This process reads the current .LMK and/or .SUM files as part of the processing. If you have made any changes, update (process U) the landmark before choosing Option V. Find V, Z or PTG.

(Compiled by JRW)

Find_V_Z_or_PTG (last edited 2016-02-19 14:17:08 by BMittan)