MAGNET Field: Correct prism settings for surveying and setting out

Correct prism settings in MAGNET Field for surveying and setting out.

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MAGNET Field: Correct prism settings for surveying and setting out

ATP1 360 prism

Ensure the prism is clean and none of the faces are damaged.

Make sure that you use the correct carbon robotic pole with the 1.42 m marking and that the black 26 mm spacer is always attached.

Ensure the correct prism constant has been set in MAGNET Field.

Note: The prism constant for the ATP1 prism is -7.0 mm.

What is a prism constant?

Note: Prism constant/offset refers to a value that compensates for the extra distance the laser beam travels through the prism in order to reach the plumb line once it initially hits the glass. It changes with differing construction and therefore changes with each prism type. Using the wrong prism constant will lead to systematic errors in a survey.

Note: Vertical height is always measured from the base of the pole to the centerline of the prism. If unsure of the value, check the documentation supplied with the equipment or speak with the supplier. It may also be good practice to always take a manual measurement using a hand tape as a check before taking any observations, especially if it is a new prism type.

Setting the correct prism constant in MAGNET Field

To create or edit prism parameters in MAGNET Field, use the gears icon.

Prism settings can be changed by pressing the gears icon at the top-right when in the Backsight, Resection, Survey, or Stake screens.

Press the gears icon, then Next to proceed to the second page.

Under Survey Settings, select the prism (for example, ATP1 360) from the Forsight P.C drop-down list. Press the ellipsis (...) button to ensure the constant is correct.

Press the green check mark to confirm the selection.

Adding a new prism

To add a new prism constant, enter the second page of the Survey Settings menu, and press the ellipsis (...) button next to Foresight P.C.

On the Prisms screen, select New.

Enter a Name and the correct Constant for the new prism type. Make sure that Hybrid Positioning antenna offset is NOT checked. Press the green check mark to save the new prism to the list.

When the new prism type is required, select it by pressing the prism icon and Edit. Ensure the green check mark is beside the required prism (as in the image above). The constant will then be applied to future measurements.

Changing measurement modes and settings

The EDM button located at the top-right of the Survey or Stake screens allows you to change the instrument measurement mode at any point.

Select between required target modes here. Switching will also change the icon visible at the bottom-left of the screen.

When using the ATP1, ensure Prism is selected. This will display the selected prism constant on screen.

If undertaking reflectorless work, select Non-Prism. The icon will change to a laser beam and wall.

If measuring to retro targets, select Sheet. The icon will resemble a laser beam and retro target.

Selecting the Laser Pointer On function emits a red laser that can be used to identify or sight targets if required. To turn the laser off, select Off.


Furthermore, these buttons can be customized depending on the required application.

Press either one of the top two options from the EDM menu.

Survey or Stake Settings will be accessed depending on which screen you are currently in.

Instrument measurement speed/update rate for both methods can also be changed via the EDM Mode drop-down menus.

Note: Selecting Tracking when using a prism is acceptable, but for the most accurate, repeatable non-prism measurements to diffuse surfaces such as concrete or brick, select Fine.

You can also command the instrument to take a number of measurements and store these as a single average by entering values in the Average boxes. Different values can be set under either the Quick or Precise buttons if required.

Precise mode has an option to Measure Continuously when using non-prism only. This can be useful when checking if a particular element is plumb, for example. This removes the need to keep pressing the measure button.

To enable this, check the Measure Continuously box, and press the left Precise button ONLY once when required. Remember to select the red X to discard or green check mark to store when finished.