In order to do topographic mapping or create ortho photo's it is necessary
to have surveyed ground control that are visible in the photography.
Objects such as aerial targets, paint lines, and catch basins or similar
are acceptable features. It is necessary for these points to be
visible in at least 2 photos or more in order to view them in
stereo.
HV - Horizontal
and Vertical coordinates on a feature such as catch basin.
V - Vertical
coordinates at a location. May require X,Y coordinates in addition.
Green
boxes may also appear on the photo and are used for the surveyor to
be able to relocate a ground control point if needed.
Yellow shading may also appear if areas are heavily obscured by shadow
or dense tree cover.
Descriptions of the points are provided on the back of the photo to
help locate point in the field.
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