Standard errors were assigned to GCP coordinates based
on lidar instrument manufacturer recommendations (x, y)
and elevation accuracy assessment results (z, see Table 1).
Standard errors of GCP coordinates allow the collinearity
adjustment equations of the photogrammetric triangulation
process a degree of flexibility in order to reach a solution
(Wolf and DeWitt, 2000). All swath-centre GCPs were
assigned standard errors of ±0.5m in x, y (Optech, 2005)
and ±0.25min z. This estimate was based on a residual rootmean-
square (RMS) error of 0.14m between lidar elevations
and check data on the ice (Table 1) and takes account of
the expected lower accuracy of GCPs extracted from steeper
sloping rock terrain surrounding the glacier surface. Swath
edge GCPs were first assigned the same standard error as
swath-centre GCPs, but were then increased to 0.5m z
to account for expected lower accuracy at swath edges.
Photogrammetric model solutions were processed using
both of these standard error configurations for swath-edge
control points.