Are there any published coordinates available for these types of control points?
I don't want to use them for survey control, rather simply add them as a spot elevations on the quad.
Principal Points in photogrammetry are the intersection of the fiducial marks on an aerial exposure, thus being the optical and geographic center of the photograph. This intersection marks the center of the photo exposure, and is one of the limits used in mapping of an aerial model.
Because of tilt or crab during the aerial photo flight, the principal point does not necessarily correspond with the location on the ground directly below the camera lens at the moment of exposure (that point is called the Nadir Point). If the photo was exactly vertical, then both PP and Nadir would be the same.
So, in theory there is nothing on the ground at these principal point locations. They are the Photo Centers of each aerial exposure along a flight line.
Points have no length, width, nor principles....;)
epoch date, post: 398831, member: 485 wrote: Principal Points in photogrammetry are the intersection of the fiducial marks on an aerial exposure, thus being the optical and geographic center of the photograph. This intersection marks the center of the photo exposure, and is one of the limits used in mapping of an aerial model.
Because of tilt or crab during the aerial photo flight, the principal point does not necessarily correspond with the location on the ground directly below the camera lens at the moment of exposure (that point is called the Nadir Point). If the photo was exactly vertical, then both PP and Nadir would be the same.
So, in theory there is nothing on the ground at these principal point locations. They are the Photo Centers of each aerial exposure along a flight line.
Thank you. What is the purpose of including them on the mapping?
The USGS Topographic Map Symbols document says that they're only on provisional maps:
[INDENT]** Provisional-Edition maps only.
Provisional-edition maps were established to expedite
completion of the remaining large-scale topographic
quadrangles of the conterminous United States. They
contain essentially the same level of information as the
standard series maps. This series can be easily recognized
by the title ÛÏProvisional EditionÛ in the lower right-hand
corner.[/INDENT]