Ordinarily, photogrammetric determination of the X, Y, and Z 
coordinates of supplemental control points is best accomplished when 
photographic targets have been placed on the ground at an appropriate 
horizontal interval and are clearly visible when the photographs are 
measured with a comparator, and also when the photographs are utilized 
in photogrammetric instruments for accomplishing the mapping and/or 
cadastral surveying. A representative photographic target, which has 
proven to be very satisfactory, regardless of the photographic emulsion 
utilized or the photographic quality of the surrounding ground and 
vegetation, is illustrated in Figure 1. This target has been tested 
over a period of years in the use of panchromatic, negative color, and 
infrared color photography, and has served well. Likewise, it has been 
utilized where the surrounding photographic detail was dark in tone, 
medium in tone, and light, or even white in tone, and has not been 
found wanting because the target is a self-contained unit, accurately 
pinpointing the location of the station marker over which centered when 
placed on the ground. The white legs are used wherever the general 
tone of the ground or vegetation on which the target is placed is dark. 
Should the tone be gray or extremely light, black legs are preferable. 
The legs, of course, are not part of the target. They are placed on 
the ground merely to aid the user of the photographs in readily identi- 
fying each target. 
An alternative for the target in Figure 1 is illustrated in 
Figure 2. They differ only slightly in their internal shape, but not 
in color or in general pattern, or in overall size. The larger portion 
of black in the center of the latter target is desirable whenever the 
season of year and time of day the photographs are taken will cause 
intense light reflection from the brown color portions of the target. 
Whenever analog bridging methods are used, intermediate supple- 
mental pass points are usually selected, well defined, images. When- 
ever aerial analytical triangulation is employed, the intermediate pass 
points are designated by the monocular drilling of circular holes in 
the emulsion to provide stereoscopic correspondence when stereocompara- 
tors are employed. When monocomparators are utilized, it is necessary 
for each of the points to be drilled in stereoscopic correspondence so 
they will be monocularly visible on each photograph when the x and y 
coordinate measurements of each point are made. In no case, however, 
are the photographic targets drilled with a point marking instrument. 
Ordinarily, basic control spaced at an interval of approximately each 
five photographs in the flight strip will suffice. Should it be not 
possible to tolerate errors as large as previously indicated in the 
tabulations, additional basic control must be provided and a larger 
number of photographic targets utilized. A large number of targeted 
points intended for use as supplemental control, the X, Y, and Z coor- 
dinates of which will be determined photogrammetrically, are advantage- 
ous and economically beneficial. Likewise, targets are placed on 
property boundary points for photogrammetrically making cadastral 
surveys of adequate precision. Of course, basic control for such work 
must be of second order accuracy or better. 
Cadastral Surveying by Photogrammetric Methods--The techniques 
and procedures described for photogrammetric determination of supple=- 
mental control have been proven adequate for most of the cadastral 
surveying required to evaluate and procure parcels of property for the 
highway right-of-way.