2. PREPARATION FOR MEASUREMENT
2-7
2.6 The Lay Position of Multiple Prisms
To increase measurement range, multiple prisms can be used. Arrange prism position to be symmetrical
horizontally and vertically. All prisms must be of the same type. AP-L1A tracks to a point where it finds
the greatest signal strength. (See diagram below)
Using TOPCON 9 prism holder
2.7 Inclination of Prism and Measuring Error
For the best results, aim or point prisms in the direction of the AP-L1A so that maximum signal can
be returned to the instrument. Sighting prism obliquely because of inclined settings, may result in
measuring errors. These errors will be proportional to the misalignment as showing in following
graphs. The more misalignment of the prism, the more error in measurement .
Measured data can be different according to the prism constant value. This can occur when a
prism is moving. Pin-pole prism set L1 (for one-person surveying) and pin-pole prism holder L1 (for
fixed point observation) are designed to minimize measuring error in such case. Make the best use
of them. In case you are forced to use the normal prism in inclined state because there is no other
way possible, we recommend to use switching holder, prism constant value (0 or 30mm), and set
to 30mm (Compensation value of -30mm).
Prism constant value : 0mm
Prism constant value : 30mm
Inclined angle
Good example
Bad example
Tracking point
(Collimating point)
Measuring
point
Instrument
point
Inclined angle
Prism
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