NAME

fstg -- Convert Spacecraft coordinates to Gnomonic direction cosines.

USAGE

fstg input_table

DESCRIPTION

This filter will convert Spacecraft coordinates to Gnomonic direction cosines. The filter searches data tables, row by row, looking for rows where FRAME=S, indicating a Spacecraft coordinate. When a Spacecraft coordinate is found, the X, Y, and associated covariances are converted to Gnomonic direction cosines using quaternion multiplication. (The transforming quaternion is computed using data columns Q1, Q2, Q3, and Q4, where Q4 is the scalar part of the quaternion.) If an error occurs in retrieving the position information, the star is skipped. An error that occurs when retrieving covariances will only cause the covariance transformation to be skipped.

Each column is read and its value set to INDEF. If an error occurs anywhere in the transformation, the row is skipped and the values remain INDEF. The FRAME column is set to G regardless of whether the transformation was completed or was incomplete.

This conversion does a simple multiplication of the quaternion formed from the negative of the roll angle and the position, as follows:

		   +
	(x',y') = Q(-roll) (x,y) Q(-roll) 

The following columns are used by fstg:

	INPUT		OUTPUT
	-----		------
	X		X
	Y		Y
	X_X		X_X
	Y_Y		Y_Y
	X_Y		X_Y
	FRAME		FRAME
	Q1,Q2,Q3,Q4	Q1,Q2,Q3,Q4

PARAMETERS

input_table [file template]

The table to be converted. This can be either an individual table or a list of tables.

(output_table) [file template]

If the new_table parameter is true, the user will be prompted to enter the output file name in which transformed tables are to be stored. Using a separate file will avoid overwriting the original data table. Output_table will accept a file name template when processing a list of data tables.

(new_table = no) [boolean]

Create a new table for output? Prevents the original table from being overwritten.

(verbose = yes) [boolean]

Print transformed coordinates on the terminal screen?

EXAMPLES

1. Convert a data table from Spacecraft to Gnomonic coordinates.

	cl> fstg intable

2. Convert a data table from Spacecraft to Gnomonic coordinates, and create a new output table.

	cl> fstg intable new_table+ output_table="outtable"

3. Process all tables having the suffix .tab.

	cl> fstg *.tab

BUGS

SEE ALSO