Vaisala IRIS, User Manual

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10.3 Overlay Header
Absolute Coordinates
If the overlay is defined in absolute coordinates, all points in the overlays are given in terms
of a longitude, latitude coordinate pair. This sets an absolute position for each point.
The following header commands must be included at the top of the overlay file:
Table 22 Overlay Latitude and Longitude Header Commands
Command Description
PROJECTION latlon
Informs system overlay is in absolute coordinates.
DRAW_CENTER lon lat
Tells Overlay where to center the image.
Generally this is the either the coordinates of the radar site, or a nearby
special area of interest such as an airport.
FILL_CENTER lon lat
Specifies center of fill area. Typically this is the center of the array of data
points you have generated.
FILL_RANGE range
Sets the maximum range that the underlay covers, in km.
Overlay draws a circle at this distance from the fill center before filling the
underlay.
Relative Coordinates
If the overlay is defined in relative coordinates, all points are defined in terms of map units.
Map units are any arbitrary unit of measure that is E/W and N/S of an origin (0,0), which can
be anywhere on the map.
Often millimeters from graph paper are used to designate the points on a map. The map
must be in azimuthal equidistant projection, with the specified reference point. A scale
factor specifies the conversion between these map units and distance on the surface of the
Earth.
The following header commands must be included at the top of the overlay file:
Table 23 Overlay Map Unit Header Commands
Command Description
PROJECTION aed
Informs system overlay is in relative coordinates.
SCALE scale
Sets the scale factor in km/map unit.
The
SCALE n command must be used to specify how many kilometers
each map unit specifies.
For example, if a
RADAR 100 200
and a
SCALE 0.5
command are
used, then if later a point is specified as POINT 110 200 , this point is
exactly 5 km due east of the reference position.
RADAR x y
Sets the projection point in map units and specifies the location of the
reference point in the map units.
REFERENCE lon lat
Sets the projection point in absolute coordinates.
IRIS Product and Display User Guide M211319EN-H
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