Google Maps/Google Earth surveying
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The surveying service uses cartography and elevation data of Google Maps/Google Earth (in order to extract the DEM*).
To use the service you need to:
- Identify the area to be detected by typing the address or coordinates;
- Choose from the drop down menu the number of points to detect: the larger is this value, the more accurate the survey will be;
- Change the zoom and move the displayed area in order to identify the portion of the surface on which to perform the survey: the maximum detectable size is about 1600 hectares;
- Click on "survey" to perform processing. After the process, you will see a grid above for each vertex the elevation in meters. You can then extract the DEM and satellite maps clicking on the appropriate buttons.
(*) The DEM is the digital model of a 3D surface, ie the representation of the distribution of elevations on a ground in correspondence of an array of dots arranged at a predetermined spacing.
N.B.: The accuracy of the altimetric data varies from 3 arc-seconds (1 point every 90 meters) to 1/3 arc-second (1 point for every 10 meters), up to 1/9 arc-seconds (1 point every 3 meters) in the U.S. and in many urban areas. The service, made available from Google Maps and Google Earth, comes from the Shuttle Radar Topography Mission (SRTM) project (http://www2.jpl.nasa.gov/srtm/), U.S. Geological Survey (USGS) (http://www.usgs.gov/) and others cartographic service. By performing surveys on some sample areas (according to studies in Italy and Nigeria) it's showed a average error about altimetric data of 2,5 meters.. The mapping with satellite maps is always relative to the Google Maps service.
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