WebÞing

The comp10d lens

The comp10d lens, like the Query lens, extracts a high-resolution scene from a global overview. The two serve slightly different purposes:

  1. The Query lens extracts exactly the area highlighted.
  2. The comp10d lens adjusts the scene to match the EDC "comp10d" facility, so you can load data from the Global 1KM AVHRR Dataset directly into the scene.

EDC's "comp10d" is the utility that extracts scenes from their AVHRR archive via the WWW. To use comp10d from the EDC webpages, you specify four coordinates, for West, East, North and South. These are labelled internally as "upper left" and "lower right", which is how the comp10d lens emulates them. As you drag the comp10d lens, your actual query is defined as follows:

  1. The Upper Left and Lower Right corners of the lens define the exact coordinates that will be sent to EDC's server.
  2. The actual area will be increased if necessary to span the east-west distance you have defined over the full north-south span of the Lens.
  3. The area will then be rounded up to the nearest multiple of 128 pixels in the full 1KM-resolution image.

This is the exact behaviour of EDC's comp10d, and is emulated by the comp10d lens. To help you see exactly the area your query defines, the comp10d lens highlights it as you move it around. To avoid possible problems arising from rounding errors, the comp10d lens will query the EDC server to confirm the exact coordinates when you use it to extract a scene.

See also