Satellite Exploration of Thailand > Satellite Image Resources

Google Earth and Google Maps




Much has been written and detailed about Google Earth and, to a lesser extent, Google Maps. Following are a few technical notes for satellite explorers.

1. Both Google Earth and Google Maps use the same satellite image data set. Other than where the high-resolution Quickbird image is available, Landsat image (RGB=321?, Band 8 enhanced) is provided. The Landsat image is mostly composed from freely distributed data set (as available at the ESDI) and not necessarily the newest or the clearest.

2. Adjoining Google Maps images can be stitched pixel-for-pixel to compose a larger image. Google Earth images, on the other hand, are subject to following irregularities:

  1. The capacity of the graphic card of your computer may limit the size of the "Detail Area" (Tools > Options > View > Detail Area).
  2. Google Earth's 3D image processing causes peripheral aberration. To view a "flat" image, you need to turn off the "terrain" layer - or set the Elevation Exaggeration to 0 (Tools > Options > View > Rendering).
  3. Google Earth reproduces images at various zoom levels (eye alt) from the downloaded source data. This most often causes sub-pixel translation when the image is panned.


3. It is possible to identify the acquisition date of a specific image by comparing with corresponding images from other sources. Exercise deduction and observation. The distribution pattern of the cloud is a definitive clue. For Quickbird images, you can browse the Digital Globe Archive Search and compare with their catalog images.



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See also Keyhole - the precursor to Google Earth

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