PLAX

Calculates parallax at cursor position.

Format

PLAX height direction [keywords]

Parameters

height	cloud height in kilometers
direction	direction for computed parallax; specify one of the following:
	CG	cloud-to-ground parallax (default)
	GC	ground-to-cloud parallax

Keywords

LATlon=	lat lon	moves the cursor to the specified latitude and longitude and calculates parallax (default=current cursor position)
STAtion=	moves the cursor to the specified station and calculates parallax; specify as the station ID, e.g., KMSN or YSSY, optionally followed by the station type in brackets, e.g., ARX[N] or ARX[V]; see the TYPE keyword in the STNLIST command for valid station types (default=current cursor position)

Remarks

If you don't specify height or direction, PLAX calculates the change in parallax at the cursor location as height increases. The information is listed as the change in degrees latitude and longitude per kilometer of height. The Position error line indicates the ground position error in kilometers at the cursor location, based on the parallax correction for a feature 10 kilometers above the earth.

If you specify height, and CG for direction, you define a point in the clouds at the specified height. PLAX calculates and plots the ground location under the given cloud point. The ground location is shown as a 7x7-pixel cross in graphics color level 3. The text output lists the latitude and longitude for the cursor point on the cloud and for the calculated ground point.

If you specify height, and GC for direction, you define a point on the ground. PLAX calculates and plots the cloud location at the specified height over the given ground point. The cloud location is shown as a 7x7-pixel cross in graphics color level 3. The text output lists the latitude and longitude for the cursor point on the ground and for the calculated cloud point.

PLAX does not work with most polar-orbiting satellite data because the navigation does not include the information needed by PLAX to do its computations.

Examples

PLAX

This entry lists the change in parallax at the cursor location as height increases. The information is given as the change in degrees latitude and longitude per kilometer of height. The Position error line indicates the ground position error in kilometers at the cursor location, based on the parallax correction for a feature 10 kilometers above the earth.

PLAX 10 LATLON=45 120

This entry moves the cursor to 45°N, 120°W and calculates the cloud-to-ground parallax at 10 kilometers above the earth. The command also plots the ground point that corresponds with the specified cloud point.

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