Fig 1
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Targets
Pre-targeting control points is always best when possible. Because it is helpful to occupy the point, it can be even more important on rural jobs where G.P.S. is utilized. A good rule of thumb when placing targets is to make the leg length about 3-4 times longer than the width (W). The signal should be centered over the control point, flush with the ground with the actual ground elevation reported regardless of where the pin is in relation to the surface. Where necessary a "T" can be used instead of a cross by eliminating one of the legs. M.A.N. does not recommend placing signals in the shape of chevrons but if it can not be avoided the control point should always be located at the tip.
Approximate Sizes
Map
Scale | Probable
Photo Scale (ft/in) | Width (w) in ft |
| 20-50 | 200-400 | 1.00 |
| 50-100 | 400-600 | 1.50 |
| 100-200 | 600-1000 | 2.00 |
| 200 | 1000-1500 | 2.50 |
| 400 | 1500-2000 | 3.00 |
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Fig 2
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Photo I.D.
When pre-targeting is not an option, control values must be obtained on locations that can be readily identified and precisely measured in the stereo instrument. These locations will be identified and described on the control print (Fig 2). They will also be marked with a pin prick so that anyone in the field can get a better idea of the exact location by holding the photo up to the light and observing with a magnifying glass. It is the surveyors responsibility to record the point in the described location to avoid delays caused by mis-identification. When the situation on site makes it impossible to get the exact point requested the field crew may need to call M.A.N. for alternate locations or if that is not possible, record multiple similar points as near as possible to the original. Any relocation of points should be clearly indicated and described in detail on the control prints.
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After mapping limits are verified and initialed on the prints, the control should be saved as an ASCII file with Point Numbers, Northing, Easting, Elevation, and optional descriptions then sent on floppy or by email to M.A.N. Mapping.
Note that work can not start on a project until the control prints are returned.
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