WHERE AND HOW
Download USGS Satellite Imagery at http://earthexplorer.usgs.gov/
Create account and either search or click map of desired area - feature.
Enter date range. 2000 - to today.
Height maps = Digital Elevation> ASTER GLOBAL DEM
High Res Colour maps = Aerial Imagery>High Resolution Orthoimagery
‘Show Browse Overlay’ displays a preview of the satellite image on top of the world map
‘Show Metadata and Browse’ contains dates, coordinates, etc.
Tile size = 1° lat x 1° long
1° x 1° = 111.699km at equator 110.567km at poles.
average = 111.133km
3601 columns x 3601 rows
pixel size = 1 arc second
1 arc second = 30.87m (? I guess this also changes)
3601 x 30.87 = 111.16287 km (? this number comes out a bit above the average)
*Either stick to average or use Area by Lat Long coordinates for exact measuments)
16bit TIFF with 65,536 levels of grey and -9999 levels for voids (Ocean, caves etc)
Sea level = 9,999 grey.
So for land elevations relating to sea level need to add 15.257% to remap accounting for voids. (9999/65536x100)
Inherent 95% accuracy with 17m degree of error in height.
Which allows for a small % to add or reduce elevation in Houdini etc.