1 Spatial Modelling of the Terrestrial Environment - Georeferencial

Remotely Sensed Topographic Data for River Channel Research 119
Figure 6.2 (a) The default photogrammetrically acquired Digital Elevation Model for the
Waimakariri River at Crossbank in February 2000 and (b) with inundated and vegetated areas
removed using unsupervised classification
precision. In some situations, it may be possible to classify different areas in a surface
as having different precisions (see below) and apply equations (3)–(5) accordingly (i.e.,
regional estimates of precision). However, even then, methods must be developed that:
(1) identify and correct localized error, which will essentially remove blunders; and (2)
remove ME, which should deal with the effects of incorrect functional models, as these
will commonly affect many points over a wide area, rather than individual points. If blunders
and inaccuracies can be removed, then the precision of a region of a surface will be the
same as individual data points that constitute that region, and regional measures of data
quality become valid.
6.3.3 Error in the Waimakariri Study
Many of the points made in sections 6.3.1 and 6.3.2 are illustrated by considering a default
DEM collected as part of the Waimakariri study (Figure 6.2(a)). This shows that there is
clearly error in the surface. An obvious cause of photogrammetric failure is where the river