7 Checks Before Proceeding with Control Point Surveying Using a Total Station

Control point surveying using a total station is an important task that forms the foundation of field surveying. If there are errors in the position or elevation of control points, the impact extends to subsequent batter board layout, as-built verification, stakeout, and the preparation of construction management documents. Even if the measurement itself can be completed in a short time, proceeding without sufficient pre-checks often leads later to mismatched coordinates, mistaken azimuths, elevation discrepancies, or insufficient records, resulting in re-surveys and rework.

A total station is a highly practical surveying instrument capable of handling distance and angle measurements, but only when setup conditions, line of sight, instrument station, backsight point, prism height, coordinate system, and recording methods are all in place will it yield consistent, reliable results. In control point surveying, it is important not simply to choose a place that can be measured, but to check whether it can be treated as a point that will be easy to use in subsequent work, easy to verify, and easy to explain. For public works and client-specified tasks, prioritize checking site-specific specifications, surveying plans, and instructions from supervisors and managers.

In this article, we organize into 7 points the items you should check before proceeding with control point surveying using an optical total station. We explain them from a practical, jobsite-oriented perspective that is easy to apply across a variety of sites, such as public works, land development, road construction, exterior works, and solar power plant construction sites.

Table of Contents

• Confirm the purposes and applications of control point surveying.

• Confirm the coordinate system and vertical datum to be used.

• Check the condition of known points and the backsight point

• Check the inspection status and settings of the total station.

• Confirm the installation environment and line of sight for the instrument point.

• Confirm the method for recording mirror height and observation conditions

• Confirm the post-observation verification procedures and data management.

• The reliability of control point surveying results depends on pre-survey verification.

Confirm the purpose and uses of control point surveying

Before starting control point surveying with a total station, the first thing to confirm is the purpose for which the control point will be used. Control points can serve different roles depending on the site: points used as the survey datum for the entire site over a long period, temporary points used for layout during construction, points used to assist as-built verification, or points intended to be handed over to another survey crew. If points are established while their purpose is unclear, they may be inconvenient to use later or may lack the required accuracy or documentation.

In control point surveying, installing a point itself is not the objective. The objective is to create a condition in which subsequent surveys and construction checks can be carried out reliably based on that point. Therefore, before setting up a total station for observation, it is necessary to confirm what scope of work the point will be used for, who will use the point, and how long it needs to be retained. For example, on sites where the terrain changes significantly, such as earthworks, points can be lost as construction progresses. In roadworks or external works, placing points along the routes used by heavy machinery or materials increases the risk of damage or displacement.

Also, when control points will be used later for as-built measurements or for organizing inspection records, it is important to keep them in a state where you can explain the point name, coordinate values, elevation, installation location, observation date, observer, equipment used, and verification method. Even provisional points used only within the site can easily cause confusion if different workers call them by different names. Rather than using vague expressions like “the point near the entrance” or “the stake on the north side,” decide on point names and link them to drawings and coordinate lists to reduce mistakes in subsequent work.

Control point surveying with an optical total station should not be evaluated solely by the readings taken at the time of observation; rather, it must be judged by considering how those points relate to the overall site operations. This is especially important on sites where multiple work teams are involved, where it is insufficient for only the surveyor to understand the points. By organizing them as control points that construction personnel, site management, and subcontractors can use with the same meaning, it becomes easier to improve the reproducibility of layout and verification work.

Confirm the coordinate system and vertical datum to be used

In control point surveying, special attention should be paid to the coordinate system and the height datum. Measurements obtained with a total station are converted into coordinates based on conditions such as the instrument station, the backsight point, the input coordinates, the orientation, the instrument height, and the mirror height. Therefore, unless you confirm in advance which coordinate system is being used and which height datum is being referenced, the measurements themselves may appear consistent yet not match drawings or other survey results.

On site, sometimes a public coordinate system is used, and other times a local coordinate system set up for the construction is used. Design drawings, construction drawings, existing survey results, and coordinate data provided by the client are not necessarily created on the same assumptions. If the orientation of the plane coordinates, the origin, the units, the number of digits, the sign of the coordinates, or the handling of X and Y differ, the resulting positions can be displaced even when correctly observed with a total station. In particular, when using a coordinate list received from other software or other equipment, it is important to check the order and units of the coordinates before entering them into the instrument.

The same applies to elevation. You need to clarify whether to use geodetic elevation, a temporary benchmark on site, or the design elevation as the reference. If height references are mixed, you can end up with correct plan positions but incorrect as-built heights. When handling elevations with a total station, inputs such as instrument height and prism height, the elevation values of known points, and the observation method all affect the results. In particular, input errors in prism height tend to appear as height discrepancies, so it is necessary to make a habit of checking them before observations.

When verifying the coordinate system and elevation datum, it is important not to judge based only on the information shown on the drawings but to cross-check with the points actually used on site and with past survey results. If reference points are already being used on site, check which documents the coordinate values are based on and whether there is any history of later revisions. If old and new coordinate tables are mixed, the same point name may have different values.

Before proceeding with control point surveys using a total station, it is safer to consolidate the coordinate data used for the work into a single source and clarify version control. Recording the coordinate table’s creation date, update date, creator, and scope of use makes it easier to explain the results later when verifying them. In control point surveys, verifying coordinates before observation greatly affects the reliability of the results.

Check the status of known points and backsight points

In control point surveying with a total station, the relationship between the instrument station and the backsights is critically important. If there are errors in the coordinates or elevations of known points, those errors will be propagated to newly established reference points. Likewise, if the selection or verification of the backsights is inadequate, the setting of direction angles can be offset, potentially affecting the entire measurement area. Before beginning surveying, it is necessary to verify on site that the known points and backsights are actually in usable condition.

When checking known points, first confirm that the point names match the field markers. If the point names on the drawings, in the coordinate table, and displayed on site do not match, it can lead to misidentification. If point names are fading or if there are multiple nails, stakes, or markings in similar positions, do not make a hasty decision; verify them against the surrounding positional relationships and past records. Be especially careful near pavement surfaces and structures, as old marks may remain from construction processes.

The condition of the point itself is also important. Check whether the pins or stakes are loose, whether there is any settlement or tilt, and whether the surrounding ground has moved. Reference points can affect subsequent work even with small displacements. Even if there is no visible problem, if there has been nearby excavation, embankment, or heavy equipment traffic, it’s reassuring to check consistency—such as verifying distances and directions to other points—before using it as a known point.

The backsight point is an important reference for determining direction. If the backsight distance is extremely short, slight sighting errors are more likely to affect the angle. Also, using a point with poor line of sight or where a mirror cannot be stably installed as the backsight can make observations unstable. It is desirable to choose a backsight point that can be sighted as clearly as possible, allows the mirror to be set securely, and will not move during the work.

After checking the known points and the backsight, do not simply measure once with the total station and call it done; where possible, perform cross-checks with other directions or other points. By verifying that the distances, angles, and elevation differences between known points do not differ markedly from existing records, you may detect input errors or point mix-ups. In control point surveying, it is essential to confirm the reliability of the base points before creating new points.

Verify the inspection status and settings of the total station

To carry out control point surveying steadily, you need to check in advance the condition and settings of the total station to be used. At the site, there are times when you want to start observations immediately after setting up the instrument, but if the instrument’s inspection status or settings are not correct, no matter how carefully you sight, the results will remain uncertain. Because control point surveying forms the foundation for subsequent work, it is important to inspect the instrument’s condition more carefully than for ordinary position checks.

The first things to check are the leveling of the total station, centering, the readings of the spirit level and electronic bubble, the telescope’s sighting condition, and the stability of distance measurements. If you observe conditions such as difficulty achieving level when mounted on the tripod, the readings shifting immediately after leveling, or the line of sight not remaining stable, check the installation site and the condition of the tripod as well. Not only the instrument itself, but also the tightening of the tripod legs, the sinking of the spike feet, and the securing of the tribrach affect measurement accuracy.

Next, check the settings inside the instrument. Verify that the distance unit, angle display, measurement mode, prism constant, the handling of atmospheric correction, the number of digits for coordinate input, and the data format to be recorded match site operations. A total station may retain the settings from its previous use. If settings used at another site, under different measurement conditions, or with a different mirror remain, they may not be suitable for the current control point survey. Before observation, check the initial screen and the settings screen, and adjust them to the working settings as necessary.

You must not overlook the condition of mirrors and reflectors. Dirt, scratches, moisture on the prism surface, looseness in the mounting parts, the pole’s scale markings, or misalignment of the bubble tube can affect the measurements. In control point surveying, you need to consider not only the EDM instrument itself but also the mirror-side conditions as a single measurement system. If the scale for reading the mirror height is hard to see, or if the pole’s telescoping section cannot be securely fixed, it is safer to replace or check them before measurement.

Also, check the battery level and recording capacity. If the power goes out during an observation, the continuity of the records can be lost and you may need to re-observe under the same conditions, increasing the amount of work. In control point surveying, it is also important to be able to verify observation data, point names, timestamps, and conditions afterwards. Confirming that the device's date and time settings, job name, and save location match the site name and the work being performed will also reduce confusion when organizing data.

Verify the installation environment and line of sight at the instrument station

When conducting control point surveys with a total station, the setup environment of the instrument station directly affects the stability of the results. It is not enough to simply place the instrument over a known point. You need to confirm that the tripod will stand stably, that it will not settle during operations, that it will be resistant to wind and vibration, and that it will not interfere with nearby work traffic. In control point surveying, even small disturbances in the setup can influence the observations, so verifying the environment before setup is essential.

On soft ground, tripod legs can gradually sink and the leveling can be disturbed. Special care is required on freshly placed embankments, areas with a thick layer of crushed stone, muddy ground after rain, and subgrades before paving. Even if a tripod appears stable immediately after being set up, slight movement can occur from people walking nearby, wind, or vibrations from heavy equipment. Choose instrument point locations where the legs can be firmly secured and where they are unlikely to be contacted during work.

Checking the line of sight is also essential. A total station assumes that it can sight a prism/reflector or an observation point from the instrument station. In control point surveying you often need to look in multiple directions—known points, backsight points, newly established points, and check points—so being able to see in only one direction may not be sufficient. Before observations, actually sweep the telescope to confirm the line of sight and verify that it will not be obstructed during work by people, vehicles, materials, temporary structures, heavy machinery, vegetation, or similar.

The position of the sun and backlighting can also affect observations. In areas with strong reflections, low evening sunlight, wet pavement, or near metal surfaces, sighting can become difficult. Also, near pavement or roof surfaces in summer, air shimmer can make sighting unstable. When measurements fluctuate, you should suspect not only equipment malfunctions but also environmental conditions along the line of sight.

Decide the locations of instrument points with consideration for whether they will be easy to use not only now but also for subsequent work. In control point surveying, the same point may need to be checked later or handed over to another surveying team. If instrument points or newly established control points are located within material storage areas, vehicle access routes, planned excavation zones, or near temporary structures scheduled for removal, they may become unusable later. Review the site schedule and select positions that are, as much as possible, easy to preserve and that provide a clear line of sight.

Confirm the method for recording mirror height and observation conditions

When conducting control point surveys with a total station, recording the prism height and the instrument height is extremely important. These items are often neglected in tasks that only check planimetric positions, but in control surveys that include elevation, errors in the entered values will affect the results. In particular, when measuring multiple points while changing the prism height or when working with multiple people, you must reliably record which point was observed at which height.

Check the mirror height not only by reading the markings on the pole but also by confirming exactly which points the height refers to. Determine whether the height is to the center of the mirror or to some other reference point, and avoid misinterpretation due to the specific combination of mirror and pole in use. A common situation on site is changing the mirror height but forgetting to update the instrument's input. Because the observed values can look plausible at first glance, this often goes unnoticed and later becomes a problem as a height mismatch.

The instrument height is the same. When measuring the height from the instrument-point marker to the center of the total station, you need to make the measurement position, the reading method, and the recording units consistent. Even when using a tape measure or a dedicated measurement method, reading mistakes or omissions in recording can occur. If the person who measures the instrument height and the person who enters it into the device are different, it is safer not only to convey it verbally but also to leave it on paper or in an electronic record before inputting.

Recording observation conditions is also important. If you record the measurement date, time of day, weather, visibility (line-of-sight) conditions, instrument stations used, backsight points, the observer, the mirror operator, the job name, and the version of the coordinate table used, it will be easier to make judgments when verifying results later. In control point surveying, it is important not only to have the numeric results but also to be able to explain the conditions under which those numbers were obtained. In particular, when re-measurements or inspections become necessary, the burden of verification work is greatly affected by whether records of the observation conditions exist.

Recording methods should preferably be standardized for each site. Whether using a paper field notebook, notes stored in equipment, electronic files, or photographic records, make sure the point name and the measured values are reliably linked. When taking photographs, shoot an overall view of the point, a close-up, the surrounding landmarks, and an image that clearly shows the point name so it will be easy to locate later. However, because relying on photographs alone can result in missing numerical information, it is important to manage them together with coordinate tables and observation records.

Confirm post-observation cross-check procedures and data management

Control point surveying does not end when observations are made and the data are saved. It is important to verify by cross-checking the measurements and coordinate values obtained with a total station against existing records and their relationships with other points to ensure there are no problems. If procedures for post-observation checks are not decided in advance, problems may go unnoticed in the field and inconsistencies may be found only after you begin organizing the data in the office. In that case, it will be necessary to return to the site to confirm them.

After observations, first verify that the point name, coordinate values, height, instrument point, backsight point, mirror height, and observation order match the records. Mistyped point names are surprisingly common, and extra care is needed when handling similarly named points or sequentially numbered points. Even a single-character difference in a point name can cause it to be treated as a different point in later coordinate lists or on drawings. In control point surveys, not only the accuracy of the measurements but also the correspondence between point names and the survey results is part of quality.

Next, verify consistency with known points. Check whether the remeasured values for known points do not differ greatly from the coordinate table, and whether distances and directions are reasonable when checking another known point from the newly established point. Acceptable differences depend on site conditions and the required accuracy, but at a minimum you should check for obvious input errors, confusion of the backsight point, incorrect prism height, or mixing of coordinate systems. If the measurement results seem questionable, it is important to perform a simple check immediately after observation so that remeasurement can be carried out on site.

In data management, organize the storage location of data retrieved from the total station, the file name, the work date, the site name, and the coordinate system used. When data remaining on the instrument, data used in the office, and data reflected in drawings and reports are mixed together, it can become unclear which is the most recent result. Because control point survey data are referenced repeatedly in subsequent work, it is important to make version control clear at the time of saving.

Also, when handing survey data to another person in charge, provide not only the coordinate values but also descriptions of point names, installation locations, usage notes, the coordinate system, the vertical datum, and the observation date. If you hand over only the numbers, the recipient may apply incorrect assumptions. In particular, when using local coordinates or temporary benchmarks, the data cannot necessarily be directly overlaid onto external drawings or other survey results, so it is safer to leave a note.

The reliability of control point surveying results depends on preliminary checks

Before proceeding with control point surveying using a total station, it is important to sequentially confirm the purpose, coordinate system, vertical datum, known points, backsights, instrument settings, setup environment, prism height, recording method, and verification procedures. Omitting any one of these may not immediately appear as a major problem. However, because control points serve as the starting point for subsequent work, small oversights in checks can later lead to major rework.

What's particularly important is not to judge solely by whether a measurement was obtained. Electro-optical surveying instruments are highly practical, but if the input conditions and site conditions are not appropriate, they will not yield the expected results. In reference point surveying, in addition to the observed values themselves, you need to be aware of which reference those values were derived from, under what conditions they were measured, and whether anyone can later verify them.

On-site, time constraints and the sequence of operations can make you want to simplify checks. However, if you carefully verify the control point survey stage, subsequent setting-out, as-built verification, construction management, and compilation of inspection documents will be easier to carry out. Conversely, if you proceed with unclear assumptions about the control points, you may be unable to explain coordinate discrepancies or elevation differences in later stages, requiring re-surveys and document revisions.

To improve the quality of control point surveying, it is effective to institutionalize check items as field procedures instead of relying solely on the experience of operators. By deciding in advance how to name points, handle coordinate tables, record mirror heights, reconcile observations after measurement, and store data, it becomes easier to maintain consistent quality even when personnel change. On sites where multiple teams work, creating shared rules can reduce coordinate confusion and missing records.

In recent years, alongside observations made with total stations, position information, photos, notes, and construction-management data collected on site are often combined and processed. Verification tasks for control-point surveys can likewise be paired with digital management that can be shared immediately on site—not just paper records—making it easier to reduce missed checks and handover errors.

To reliably carry out control point surveying with a total station, the first step is to organize the site’s reference points and clarify the verification procedures to be performed before and after observations. Moreover, recording the site’s positional information in an easy-to-use format and establishing a system that links through to construction management and as-built verification will make it easier to share survey results and streamline site recordkeeping.