Accurate orthophotograhy is dependent upon an accurate
DEM. Orthos are typically rectified to a photogrametically compiled DEM.
However, to save project costs, orthos can be rectified to existing DEMs
such as those supplied by the USGS. The client should be aware of the
differences between these DEMs. Typical accuracy of a USGS 30m DEM is ±33'. In contrast, in a compiled DEM with a 1:400 scale the
accuracy is held to within ±4'.
Find out more about WAM's orthophoto products
|USGS 30m DEM
|Compiled 400 Scale DEM