How to Use a Total Station for As-Built Survey

Applies to: Topcon GT-1000/GT-500 series, Trimble S-Series, Leica TS16/TS07, Sokkia SX series

An as-built survey documents what was actually constructed versus what the design called for. It is required for record drawings, owner acceptance, permit closeout, and future maintenance. Using a total station gives you sub-centimeter horizontal and vertical accuracy, making it the preferred method for utility inverts, foundation elevations, and structural elements where GPS signal is blocked or specification accuracy demands it.

Step 1: Set Up on a Control Point

Center and level the total station over a control monument using the tribrach and optical or laser plummet. Measure the height of instrument (HI) from the monument top to the telescope rotation axis — this measurement directly affects all computed elevations. Record HI to the nearest millimeter in the data collector before occupying the station. Errors in HI propagate into every elevation reading taken from that setup.

Enter the control point coordinates (northing, easting, elevation) into the data collector job. Open the instrument orientation function and sight the backsight control point. Confirm the known backsight distance matches the measured distance within project tolerance — typically 5-10mm. If the distances disagree, recheck instrument centering, ensure you are sighting the correct target, and re-enter coordinates.

Step 2: Orient with a Backsight

Use a second control monument as the backsight whenever possible. Enter or select the backsight coordinates in the data collector. Aim the total station crosshairs precisely on the backsight prism or target, then press Set Orientation. The instrument now has a defined azimuth — all horizontal angles measured from this orientation are referenced to the project coordinate system.

After setting orientation, measure a check shot to a third control point (if available) before collecting production data. The check shot coordinates should match known values within 25mm horizontal and 30mm vertical. A passing check shot confirms the setup is correct; a failing check shot means something is wrong with the instrument orientation, coordinates, or control network — do not begin data collection until the problem is identified and corrected.

Step 3: Develop a Point Collection Strategy

As-built collection differs from stakeout: you are measuring what exists, not what should exist. Before beginning, review the design drawings to understand which elements need to be documented and what accuracy level applies. Common as-built elements include: pipe inverts, top-of-pipe elevations, manhole rim and invert elevations, top-of-footing, finish floor slab, pavement edge, curb face, and structure corners.

Assign point codes in the data collector before collecting — for example, "MINV" for manhole invert, "MRIM" for manhole rim, "PINV" for pipe invert. Consistent coding makes the exported data usable without extensive cleanup. Collect multiple shots on each element when tolerance is tight: average three independent readings for critical inverts and foundation elevations.

Step 4: Measure Utility and Structure Elements

For pipe inverts in manholes, lower a prism pole to the invert and center it carefully on the pipe flow line. Enter the pole height precisely. The computed elevation will be the invert elevation — the value that drives stormwater, sewer, and utility design decisions for decades. Errors here are permanent record errors.

For above-grade structures, use a reflectorless measurement if the surface is accessible. For corners and column bases, use a prism pole held plumb on the point. For rough surfaces like compacted subgrade or aggregate base, take multiple shots across the area to characterize the elevation range, not just a single point.

Step 5: Export and Deliver

Transfer the data collector file to the office computer using the manufacturer's software (Topcon MAGNET Office, Trimble Business Center, Leica Infinity, or similar). Export the point database as a CSV, DXF, or LandXML file. Import into AutoCAD Civil 3D, MicroStation, or the project's CAD platform. Compare the as-built points against the design surface or design drawings to generate a cut/fill analysis or a point-by-point comparison table for the submittal package.

Flag any points that deviate from design by more than the specification tolerance. Document which field crew collected the data, which control points were used, and the date of collection. This metadata is required for most public agency as-built submittals.

Frequently Asked Questions

What is the accuracy of a total station for as-built survey?

A modern reflectorless total station achieves 2-5mm horizontal and vertical accuracy under normal field conditions with a prism. Reflectorless measurements on rough surfaces are slightly less precise. For utility inverts and structural elements, total station as-built accuracy is typically 5-10mm, which exceeds GPS rover accuracy in obstructed environments.

How many control points do I need for an as-built total station survey?

A minimum of two control points are required per setup — one to occupy, one for backsight orientation. A third control point for check shots is strongly recommended. On large projects, establish a network of control points so you can move setups without losing orientation, and always confirm the check shot passes before beginning collection from a new setup.

Can I use a robotic total station for as-built survey?

Yes. A robotic total station (Leica TS16, Trimble S7, Topcon GT-1000) allows a single person to operate without a rod person — the instrument automatically tracks the prism on the pole. This dramatically speeds up large as-built surveys where covering ground quickly matters more than having a second person to read invert numbers.

What file format do I deliver for as-built total station data?

Most public agencies accept DXF or LandXML. Private owners often want a PDF report with point tables showing design vs. as-built with differences. CAD drawing submittals typically require the as-built points plotted over the design drawing at the correct scale and coordinate system. Confirm the required deliverable format before beginning fieldwork.