Precise elevations

If you are using a GNSS receiver for stakeout, then you don't need to maintain line of sight to a total station. Sometimes, however, you need to use a total station for better elevation control. In Trimble Access Roads you can enable the Precise elevation option to get the best of both worlds: set up an integrated survey and use the GNSS for horizontal positioning and use the total station for vertical positioning.

Because you don't need the total station for horizontal positioning you can set it up on a high point with good visibility (no horizontal coordinates are needed) and use the Station elevation feature to tie into known point(s) to set the elevation control.

When using Precise elevation, the software provides horizontal navigation based on GNSS, and vertical navigation from the total station. When you store the staked point, three point records are stored: a GNSS position, a total station position, and a combined position.

For an overview of setting up precise elevation and using it to stake out a road, watch the Integrated surveying with precise elevation video on the Trimble Access YouTube channel.

  1. In the integrated survey style you will use, select the Precise elevation check box. For more information see To configure the integrated survey style.

  2. To use precise elevations, you must switch to the Roads app. To switch between applications, tap and tap the name of the app you are currently using, and then select the application to switch to.

To set up the conventional instrument, position the instrument in a location with good visibility and safe from machinery. The elevation is determined by one or more Station elevation measurements to point(s) with a known elevation. You can set up the robotic total station on a known control point, but this is not required.

  1. Position the conventional survey instrument and then tap and select Stakeout / <integrated style name> / Station elevation.

  2. The RTK survey starts. Once the RTK survey has initialized, you can begin the station setup for the conventional survey.

  3. Set the corrections associated with the instrument.

    If the Corrections form does not appear, tap Options from the Station setup screen to set the corrections. To make the Corrections form appear on startup, select the Show corrections on startup option.

  4. Tap Accept.
  5. If required, enter the Instrument point name, Code, and Instrument height. If the instrument is not set up on a known point with a known elevation, accept the default point name and 0.000 instrument height.
  6. Tap Accept.

  7. Enter the point name, code, and target details for the point with the known elevation.

    To select a point already in the job, such as a control point, tap next to the Point name field. Alternatively, you can key in a point. The point needs only a name and an elevation – horizontal coordinates are not required.

    If you are using IMU tilt compensation for the RTK part of the integrated survey, the tilt compensation is not applied to the conventional observations. Be sure to level the pole when the Precise elevation option is enabled when surveying a road using the Roads software, and when using conventional total station measurements.

  8. Position the prism on the point with the known elevation and tap Measure. The elevation value is transferred to the instrument point. Once the measurement is stored, the Point residuals appear.

  9. From the Point residuals screen, tap one of the following softkeys:

    • + Point, to observe additional known points
    • Details, to view or edit point details
    • Use, to enable or disable a point
  10. To view the station elevation result, tap Results in the Point residuals screen. To accept the result, tap Store.

  1. In the map, tap the road and then tap Stakeout.

    The software shows a message indicating that Road stakeout precise elevation is enabled.

    If you are using a GNSS receiver with IMU tilt compensation, the message warns that you must level the pole for as-staked observations, because tilt compensation is not applied to the conventional observations.

  2. Tap OK to dismiss the message.

  3. The road is ready to stake, using your preferred stakeout method.

    During stakeout, the software provides horizontal navigation based on GNSS, and vertical navigation from the total station.

    When you store the staked point, three point records are stored: a GNSS position, a total station position, and a combined position.

If the robotic total station cannot measure to the target, the cut/fill and vertical distance values are shown as "?".