Object catalog / elevation
Note that this table is very large, almost 50 billion records. Do not attempt to download the entire table.
Ground data is derived from elevation products provided by the United States Geological Survey (USGS). Specifically, the elevation table contains 1 arc-second resolution data points. This data is sourced from 1-degree by 1-degree geotiff files and covers most of North America.
Geotiff files encode elevation data into images. For 1 arc-second of resolution, each pixel represents the height of a plot of ground measuring 1 second of latitude and longitude. This translates to approximately 101 feet per latitude. Note that the length of a degree of longitude changes with latitude and will only be 101 feet at the equator.
Elevation data is stored in a simple table with 3 fields: Lon, Lat, and Elevation.
Lon and Lat are stored as tenths of a second. You can convert back to decimal degrees by dividing by 36,000. Each longitude and latitude represent the mid-point of the corresponding pixel. For example, assume a 1 arc-second pixel with its top-left corner at -100°W, 35°N. This translates to a box with the following coordinates:
| -3600000, 1260000 | -3599990, 1260000 |
|---|---|
| -3600000, 1259990 | -3599990, 1259990 |
The values stored in the elevation table for Lon and Lat will be -3599995 and 1259995.
Elevation is stored in meters above (or below) sea level.