Nodes of different colours represent the following:
Solid arrows point from a submodule to the (sub)module which it is
descended from. Dashed arrows point from a module or program unit to
modules which it uses.
Where possible, edges connecting nodes are
given different colours to make them easier to distinguish in
large graphs.
save the object number of each defining unit
all channels are in region
read channel soft calibration data for each land use
sum total channel length for