In vastly wooded areas, man-made features
such as buildings, roads, and telephone poles are not available or are
incorrectly situated to be suitable control points. This problem usually
occurs in mountainous, heavily wooded areas and necessitates use of
pre-flight panels (targets) placed in optional positions within or near
the area to be mapped. These artificial targets are then tied into control
surveys. These targets will be used for precise measurements and to
orient the entire mapping correctly and therefore, care must be used
in producing and placing them. Target sizes vary depending on the photo
scale. Use the menu below to find out how big your targets should
be.
Round to the higher closest photo scale.
PANELS(TARGETS): The panels should be of weatherproof material and
should stand out against the background surface. An easy and economical
target can be made up with tarpaper and painted white or made of
bleached cotton sheeting, white mercerized cotton bunting or white
muslin. Caution should be exercised so sun reflection does not render
the target useless. For this reason, plastic sheeting or high gloss
material should not be used. If the target is to be placed on an
asphalt road or paved parking lot, white waterproof paint can be
used directly on the hard surface. On any concrete roadway black
paint can be used.
When placing the targets, one should refer to the general areas
marked by us on the figure accompanying the proposal. Since the
aerial photography will occur between the hours of 9:30 a.m. – 3:30
p.m. for Spring flights, and 10:30 a.m – 1:30 p.m. for Fall/Winter
flights, be certain that the targets are sunlit and shadow free
during these hours. Placement should occur within the red cross
and blue squared area on the map just prior to flight time in order
to minimize the possibility of damage or loss. The target should
be placed on a flat, but not necessarily level spot that is not
obscured by evergreen trees or dark shadows. It is best to position
the targets anywhere within the marked area that is open and free
from deep shadows (i.e. we have asked for a target on the property
corner, but that corner is obscured by evergreen trees - it would
then be necessary to move the target to an open area such as a swamp
or hardwood stand). If it is necessary to move a target more than
three hundred feet (300’), please contact us for advice.
