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2. Definitions

These terms are used throughout:

2.1. Kinds of tiles

Two kinds of image data are available from TerraServer:

  • Digital Orthoquad or DOQ tiles represent aerial photos. The tile-kind or image type code for such tiles is 1.

  • Topographic map tiles are scanned from topographic maps, such as USGS quadrangle maps. The tile-kind for these tiles is 2.

2.2. Magnification codes

TerraServer's map data is available at a number of different magnifications. Each pixel of the map covers a square whose edges may be 1, 2, 4, 8, up to 512 meters.

When we refer to a magnification code or mag-code, we mean this dimension. For example, the aerial photographs are available at magnifications up to 1 meter/pixel, a mag-code of 1. Topographic map images are easiest to read at a mag-code of 4, so that each pixel of the image represents a 4×4 meter square of ground.

2.3. Tiles

All the imagery available from the TerraServer site comes in the form of tiles, image files containing 200×200 pixels. For example, a tile with a mag-code of 4 will represent an 800×800-meter area.

The programs of this suite will take care of assembling the tiles into images. The size of these images will be a multiple of the tile size.

2.4. Flexible angle coordinates

You can use a variety of input formats to specify coordinates. To save typing, we use these conventions:

  • Numbers with 1, 2 or 3 digits are assumed to be in degrees. For example, “34” is assumed to be 34°, and “107” means 107°.

  • Numbers with 4 or 5 digits are assumed to be in the format DDMM or DDDMM, where DD or DDD is degrees and MM is minutes. So, for example, 3456 means 34° 56', and 10703 means 107° 3'.

  • Numbers with 6 or 7 digits are assumed to have be in format DDMMSS or DDDMMSS, where SS is seconds. Examples: 341638 means 34° 16' 38", and 1075301 means 107° 53' 1".

  • A trailing decimal point and fraction are always allowed. The fraction is assumed to be in the same units as the smallest unit to the left of the decimal point. For example, “3401.57” is interpreted as 34° 01.57'.

2.5. Latitude and longitude coordinates

The usual format for representing a location as a latitude and longitude is:

    lat{n|s}lon{e|w}

That is, start with the latitude using the flexible angle format described above, followed by n or s for north or south latitude, followed by the longitude in flexible angle format, then e or w for east or west longitude.

Here are some examples:

5130s0007e51°30' S. Lat., 0°7' E. Long.
34n107w34° N. Lat., 107° W. Long.
34.0242n107.1811w34.0242° N. Lat., 107.1811° W. Lat.