Plan Position Indicator
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The Plan Position Indicator, known as PPI is the most common way to represent radar data.
The signal represented is the reflectivity at only one elevation ef the antenna, so is possible to have many PPI at one time, one for each antenna elevation. The radar is usually represented in the center of the display, so the distance from it can be drawn as concentric circles.
Usually, North is represented at the top of the image, except in the case of ship and aircraft radars, where the top represents the front part of the ship or aircraft, i.e. its heading (direction of travel) and this is usually represented by a lubber line
The Plan Position Indicator was first introduced in the H2S radar blind-bombing system of World War Two.