Ashtech Z-Surveyor Service Manual download pdf (Page 35)

Survey Preparation & Execution 27

Surveying

3. Measure and record instrument height (HI) of GPS antenna

Remember that measurements of satellite data are made at the center

(horizontally and vertically) of the GPS antenna. Yet the location of the point

to be surveyed is not at the center of the antenna but below it on the ground.

The HI allows the computed position of the antenna center to be transferred to

the ground point. It is critical that the HI of the antenna above the monument

is measured accurately. A tool to measure the HI is included with each GPS

receiver (Figure 4.4).

Figure 4.3. Conventional and Fixed-Height Tripods

Conventional

Fixed-Height

630045.book Page 27 Sunday, February 11, 2001 11:38 AM

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Ashtech Z-Surveyor Service Manual Page 35