Environmental Engineering Reference
In-Depth Information
Fig. 2.7 Staff plates indicate the water level elevation with respect to the 0 m mark on the staff
plate. The color blocks are 0.01 m tall, and each decimeter is numbered. By interpolating to the
millimeter, the water level in the figure is 0.165 m. The staff plate can also be used to relate models
with field measurements
Local (arbitrary) horizontal datums are not georeferenced to a standard map
projection or coordinate system. Local horizontal datums are assigned arbitrary
values for horizontal position relative to a local benchmark to which you have
assigned a convenient position such as (0,0), (50,50), or (100,100). As with local
elevation datums, it is standard practice to make the coordinates sufficiently large
so that the positions will be positive values. Local horizontal datums can be based
on fixed structures, such as described for vertical datum, or other objects such as
rebar, bridge corners, culverts, or trees. A local horizontal datum allows all
measured points to be placed in horizontal space relative to one another, but not
necessarily referenced to other datasets that may be available. The other require-
ment for local horizontal datum to work is to define the direction of one of the axes.
It is most convenient to define one of the axes to be the long dimension of the
wetland. The axial directions can be recorded as compass bearings from a precise
compass, such as a pocket transit.
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