An important evaluation to make when performing a QAQC analysis of a LIDAR data set is a control point comparison. Typically, this refers to checking the vertical accuracy of a LIDAR data set. In regards to vertical check/control point location:
“Unlike horizontal checkpoints, vertical checkpoints are not necessarily required to be clearly defined or readily identifiable point features. Vertical checkpoints shall be established at locations that minimize interpolation errors when comparing elevations interpolated from the data set to the elevations of the checkpoints. Vertical checkpoints shall be surveyed on flat or uniformly-sloped open terrain and with slopes of 10% or less and should avoid vertical artifacts or abrupt changes in elevation.” – ASPRS Positional Accuracy Standards for Digital Geospatial Data.
There have been some customer inquiries as to the feasibility of using ground targets for horizontal check/control as well. There are several research papers that have been presented over the years. One published article by the Ohio Department of Transportation tested ground targets for horizontal accuracy assessment of LIDAR data sets:
“Results confirmed that the optimal target is rotation invariant, circular-shaped, elevated from the ground and a 1 m circle radius can provide sufficient accuracy from a point density of about 5 pts/m2 . Targets larger than 2 m in diameter will not lead to significant improvements. In addition, the two-concentric-circle design (the inner circle has one-half the radius of the outer circle) with different coatings produced considerable accuracy improvements in the horizontal position.” (Csanyi and Toth, Photogrammetric Engineering & Remote Sensing Vol. 73, No. 4, April 2007, pp. 385–396, Improvement of Lidar Data Accuracy Using Lidar-Specific Ground Targets)
