Five Tips for Placing Survey Points to Avoid Line-of-Sight Problems with Total Stations

Total stations are widely used on-site as surveying instruments that sight from the instrument station to survey points or mirrors and measure distance and angles. Therefore, even if the instrument is highly accurate, poor placement of survey points can cause problems such as being unable to sight, not being able to see the mirror, unstable measurement values, and an increase in re-measurements. This is especially true at construction sites such as land development, exterior works, roads, slopes, around buildings, and photovoltaic power plants, where materials, heavy machinery, temporary structures, level differences, vegetation, and people's movement lines change daily, so it is important to plan survey point placement in advance with line-of-sight in mind.

This article organizes and explains five easy-to-implement adjustments to survey point placement for avoiding line-of-sight problems when using a total station.

Rather than relying on the subjective judgment of simply "placing it where it can be seen," considering everything from the instrument station, backsight, survey points, mirror positions, work flow, and recording methods can help reduce rework in surveying operations and make it easier to achieve stable observations.

Table of Contents

• Main causes of line-of-sight problems in electro-optical surveying instruments

• Technique 1: Decide the survey points after first confirming the area visible from the instrument station.

• Tip 2 Prioritize positions from which both the rear viewpoint and the measurement point are visible

• Tip 3: Consider the height of survey points in anticipation of elevation differences and obstacles

• Tip 4: Place measurement points in positions that are unlikely to be obstructed during work

• Tip 5 Prepare backup points and a layout that makes re-observation easy

• Improve the efficiency of total station operations by arranging survey points to maintain line-of-sight

Main causes of line-of-sight problems in total stations

In surveying with a total station, it is assumed that the instrument station can sight the prism or target point. "Line of sight" refers to the condition in which a clear view is secured from the instrument to the point to be measured or to the position where the prism will be placed. When line of sight is poor, not only can distance measurement be impossible, but you may have to sight from awkward positions, move the prism position repeatedly, or re-set up the instrument. As a result, the planned surveying sequence can be disrupted, and the work time may increase significantly.

Causes of poor line of sight aren't limited to simply having obstacles. On site, slight changes in elevation, temporary fencing, the parking positions of heavy equipment, temporary placement of materials, slope shoulders, vegetation, existing structures, and workers passing through can all block the line of sight. Even if a point is visible immediately after the instrument is set up, as work progresses vehicles may stop or materials may be stacked, causing it to become obscured partway through. In particular, with optical distance-measuring instruments, if the relationship between the instrument point, the backsight point, and the survey point is disrupted, verifying the measurement results becomes time-consuming, so the initial placement of survey points is important.

Also, if you determine survey points by looking only at the plan view, you are likely to overlook on-site elevation differences and actual obstacles. Even where positions appear aligned in a straight line on the drawing, on site your line of sight can be blocked by embankments, excavation faces, retaining walls, temporary access routes, fences, and so on. Especially at sites with elevation differences, unless you take into account instrument height, mirror height, and ground undulations, you may find that even closely spaced survey points are not intervisible.

Poor lines of sight are not just a surveyor’s problem; they affect the overall sequencing of construction. If survey points cannot be seen and verification surveys are delayed, subsequent tasks—setting out, excavation, installation, as‑built verification, and inspection preparation—can all be impacted. When survey points are placed on the assumption that “they’ll be visible later,” they can actually be blocked by heavy machinery or materials, requiring clearing or relocation each time a survey is conducted. To prevent such rework, it is important at the survey‑point placement stage to be mindful of lines of sight and to arrange points so they are easy to observe.

In arranging survey points for a total station to avoid line-of-sight problems, you should consider not only where to set up the instrument but also which points to use as references, in what order to measure them, and where to place backup points—all as an integrated whole. Because surveying conditions change as work on site progresses, it is more practical to allow flexibility to adapt to changes than to try to create a perfect layout from the start. From the next chapter, we will look concretely at five practical techniques for survey point layout that are easy to use in the field.

Tip 1: Confirm the area visible from the instrument station first, then decide the survey points

The primary measure to avoid poor line-of-sight is not to decide survey points first and then look for instrument stations, but to confirm from the instrument station the actual visible range and then place the survey points. If survey points are decided solely for the convenience of the drawings, when you go to the field you are likely to encounter problems such as "there is no place to set up the instrument," "there is a survey point but the prism cannot be seen," or "the backsight is visible but the target survey point is not." With an EDM/total station, stable observations are possible only when the line of sight from the instrument station to the target point is secured, so it is important to first check the visibility from candidate instrument stations.

When you enter the site, first clarify the purpose of the survey. Whether it is control point surveying, batter boards or layout marking (staking out), as-built verification, or locating existing structures, the locations of required survey points and the observation range will differ. For example, in as-built verification you may measure many points along the completed shape. On the other hand, for batter boards or layout marking, because you are transferring design positions to the field, an instrument station that can oversee a wide working area can be advantageous. If you place survey points while the purpose is unclear, you will need to move the instrument to different positions more often later, so it is important to define the necessary observation range at the outset.

When selecting candidate instrument stations, simply choosing a location with a wide view is not enough. You should also check whether the ground can support a tripod stably, whether it will obstruct the passage of workers or vehicles, whether it is unlikely to be affected by vibration, and whether the line of sight is unlikely to be blocked by people or materials during measurement. Even if a wide area is visible, an instrument can shift slightly or create safety hazards during operations if the footing is soft or if it is close to heavy machinery. Because a total station handles precise angles and distances, not only visibility but also the stability of the installation is a prerequisite for station placement.

When positioning survey points, rather than imagining the line of sight from the instrument point to the survey point, it is effective to actually align your eye on site and check. The instrument height is not the ground level itself but the position where it is installed on the tripod. The mirror is also not directly on the ground; it has the height of the pole. Therefore, even if there are obstacles near the ground, line of sight can be achieved depending on the relationship between the instrument height and the mirror height. Conversely, something that looks unobstructed at ground level may have a fence, the crest of a slope, or the top edge of temporary materials entering the line of sight. When performing a visual check, it is important to be conscious of the instrument installation height and the mirror height and to view from a position close to the actual observation line.

Before deciding on measurement points, it is also effective to move slightly left and right from instrument station candidates and compare how things appear. By shifting the instrument station just a little, you may be able to avoid building corners, piles of materials, slope ridgelines, and vehicle shadows. Especially on confined sites, changing the instrument station by tens of centimeters (tens of in) to several meters (several ft) can greatly change the number of visible measurement points. Rather than rushing to decide measurement point placement, inspecting multiple instrument station candidates first will reduce later re‑setups.

Also, survey points do not necessarily have to be placed only around the perimeter of the work area. If you place points on the perimeter, they can be blocked by temporary fencing or materials during construction, or you may have to take a detour to set up a prism or mirror. Conversely, placing auxiliary survey points near the center of the work area can make line of sight from the instrument stations easier and allow the site to be divided into sections for easier surveying. Because arranging survey points is also the task of creating lines that are easy to survey, it is important to consider not only the boundaries on the drawings or the edges of structures, but also positions that are convenient as observation routes.

Getting into the habit of first checking the area visible from the instrument point stabilizes the planning of surveying work. Rather than waiting until an unmeasurable point appears and thinking it through on site, you can organize in advance which areas to measure at once and which areas to measure from a different instrument point. When laying out measurement points for an optical distance meter (total station), it is important not only to expand the visible area but also to determine the ranges that can be measured accurately without difficulty. By confirming line of sight before deciding on measurement points, you can reduce re-observations and instrument moves, making it easier to improve overall on-site work efficiency.

Tip 2 Prioritize positions with a clear line of sight to both the backsight and the survey point

To perform stable surveying with an optical surveying instrument, it is important not only that the target survey point is visible, but also that the backsight and reference points can be reliably seen. In the field, attention tends to focus on whether the survey point in front of you is visible, but if the backsight used to establish the instrument station’s direction is hard to see, the basis for observations becomes unstable. If you set up the instrument where the backsight is difficult to obtain, it can take longer to confirm the initial orientation and make intermediate checks harder, which in turn affects the overall reliability of the survey.

To choose a position that allows a clear line of sight to both the backsight and the survey points, confirm that, with the instrument station as the center, your sightline reaches both the reference-point direction and the work-area direction. If you prioritize only the survey-point side, the backsight can become obscured by buildings, slopes, heavy equipment, or temporary materials. Conversely, if you prioritize only the backsight, the line of sight to the area you actually want to measure may be poor. Because the instrument station of a light-wave surveying instrument is both a position for confirming the reference and a position for measuring the work area, it is necessary to balance both.

It is desirable for the backsight to be located where it can be found and re-sighted as easily as possible. During surveying, there are occasions when the backsight is rechecked to confirm that the instrument’s setup or orientation has not shifted. If the backsight is placed where it is difficult to see, each check will take extra time. When the line of sight is marginal, the backsight can become obscured by even slight movement of personnel or materials, so it is important to choose a location where it can be seen with some margin.

When considering the positional relationship between the backsight and the survey points, care must also be taken in how angles are taken. From the instrument station, if the directions to the backsight and the survey point are biased into an extremely narrow range, it can become difficult to confirm the entire site. Of course, this may be unavoidable due to site conditions, but arranging things so that the reference direction and the work direction are clearly distinct makes it easier to prevent mix-ups during observation. This is particularly important when measuring multiple survey points in succession: arrange them so it is easy on site to recognize which point is in which direction.

In sites where multiple control points can be used, it can be effective not to limit candidates for the backsight to a single point. If one backsight is visible but likely to be obstructed by materials as construction progresses, it is reassuring to ensure another backsight can also be checked. Not every site can provide multiple backsight points, but if there are usable known points or auxiliary points, recording which points provide visibility over which areas will speed up response when line-of-sight problems occur.

When planning the placement of survey stations, consider not only the relationship from the back-sight to the instrument station and from the instrument station to the survey points, but also the flow of checks during surveying operations. An ideal layout allows the sequence of setting up the instrument, taking the back-sight, measuring survey points, periodically checking the back-sight, and remeasuring as necessary to proceed smoothly. If you focus only on whether survey points are visible, you can end up with an arrangement that makes back-sight checks difficult and ultimately slows the entire operation. With a total station, it is important to prioritize configurations that allow measurements to be taken while maintaining the reference, rather than the number of visible points.

Also, care must be taken not to confuse survey point names and benchmark names. When multiple points are visible in a clear line of sight, it can become ambiguous which point is being used as the backsight and which point is being measured. If the on-site point name indications, the condition of stakes or pins, the point names in the field book, and the point names in the instrument do not match, measurement errors can occur even with good visibility. It is necessary not only to arrange things so that both the backsight and the measured point are visible, but also to ensure that you can reliably confirm which point you are looking at.

Prioritizing positions that provide a clear line of sight to both the backsight and the survey point makes observations with a total station more stable. Because you can repeatedly verify the reference while maintaining line of sight, there is greater leeway for re-setting the instrument and checking measurements. When deciding on survey point placement, in practice it makes a big difference to consider not only whether the target point can be seen, but also whether it can be measured while confirming the reference.

Tip 3: Consider the height of survey points in anticipation of elevation differences and obstacles

Poor line-of-sight can occur not only because of planimetric positions but also because of height relationships. Even if the instrument point and the survey point appear close on the drawing and there seems to be no obstacle between them, in reality the line of sight can be blocked by ground undulations, slopes, retaining walls, embankments, excavation steps, or the height of temporary structures. When laying out survey targets for an electro-optical distance meter, you must consider not only the horizontal positions of the points but also the instrument height, prism height, the heights of obstacles, and differences in ground elevation.

On sites with elevation differences, placing the instrument in a low location can result in its line of sight being blocked by surrounding embankments or structures. Conversely, placing the instrument in a high location makes it easier to overlook a wide area, but you must check the stability of the footing and safety. Being in a high location is not necessarily better; it is important to confirm whether the tripod can be set stably, whether the operator can work safely, and whether the setup is less susceptible to wind and vibration. Especially near slopes and temporary walkways, it is necessary to assess visibility and safety simultaneously.

The concept of height is also important on the survey station side where the mirror is set up. The survey point itself is on the ground or on a structure, but what is actually sighted is the center of the mirror. Therefore, by setting the mirror height appropriately, it may be possible to secure line of sight over low obstacles. However, if you change the mirror height, you must handle input and recorded values accurately. Because input errors in height can affect the measured elevations and coordinates, whenever you change the mirror height to secure line of sight, be sure to share that information on site and record it.

When anticipating the height of obstacles, it is easier to organize if you separate fixed obstacles from temporary ones. Fixed obstacles include buildings, retaining walls, fences, existing structures, and terrain undulations. Temporary obstacles include materials, vehicles, heavy machinery, temporary scaffolding, and workers' movement paths. Fixed obstacles need to be avoided at the stage of laying out survey points, but temporary obstacles change depending on work hours and the schedule. When placing survey points, you need to consider not only whether something is visible now, but also what might be placed there at the time of the survey.

There is also a method of securing line of sight by taking advantage of elevation differences. For example, even if viewing the entire work area from a low position is blocked, establishing auxiliary points at slightly higher positions can allow you to see multiple survey points. Also, by using ridge-like locations of the terrain or the edges of structures, it can sometimes be easier to establish lines of sight between survey points. However, it is important that survey points be not only for surveying but also re-checkable later. If a survey point placed at a high location becomes difficult to access later, or it becomes unsafe to set up a mirror, it can cause problems during re-surveying.

Even in situations where non-prism measurements can be used, the line-of-sight considerations do not change. Even when the target surface can be measured without placing a mirror, it is necessary that the target surface is visible from the instrument, that reflection conditions are stable, and that you can accurately sight the position you want to measure. Depending on the target surface’s material, angle, wetness, dirt, and sunlight, the measured values may not be stable. Therefore, rather than oversimplifying the placement of measurement points on the assumption of non-prism measurements, it is reassuring to arrange them so that mirror measurements or verification measurements can be performed as needed.

When arranging measuring points with height in mind, sharing information not only with the surveyor but also with the mirror operator and site personnel is essential. Even if the instrument operator thinks a point is visible, the mirror operator may have poor footing and find it difficult to keep the pole vertical. Even where a measuring point is visible, if the mirror cannot be set up stably it will lead to variability in the measurements. When deciding the placement of measuring points, it is important to check both the line of sight from the instrument side and the workability on the mirror side simultaneously.

By considering the height of survey points in anticipation of elevation differences and obstacles, you can reduce rework caused by poor line of sight. For the placement of points when using a total station, it is important not to judge by the plan view alone but to check the on-site height relationships and be mindful of instrument height and mirror height. If you organize the height conditions in advance, you can reduce instances of your line of sight being blocked and having to scramble during observations, leading to more stable surveying work.

Tip 4: Place measurement points where they are unlikely to be obstructed during work

When placing control points, it is important to consider not only whether they are visible at the start of surveying but also whether that line of sight can be maintained during work. On site, surveying and construction often proceed simultaneously, and a control point that was visible in the morning may be obscured by materials or vehicles by midday. Because line-of-sight failures with total stations often occur not at the moment the control point is placed but when you actually try to measure, it is necessary to devise ways to choose locations that are less likely to be blocked during operations.

First to consider are the movement paths of heavy equipment and vehicles. Placing survey points near access routes, turning areas, loading/unloading zones, or parking spots can not only obstruct lines of sight but also risk damage to the points themselves or cause them to be lost. A location that is convenient for surveying can easily become an obstacle for construction. When deciding the placement of survey points, check the site's traffic flow and avoid areas where vehicles are likely to stop or where materials are likely to be stored during surveying.

Next, be mindful of temporary storage locations for materials. On site, even when material storage areas are clearly designated, materials may be temporarily placed elsewhere for operational reasons. Materials are especially likely to be placed along roadsides, next to buildings, at the bottom of slopes, near entrances and exits, and at the edges of the work yard. If a survey point is located near these areas, sight lines can be blocked during surveying, or there may be no space to set up a surveying mirror. Survey points should be positioned so they do not obstruct construction and are easy to locate later.

Workers passing through also affect line of sight. If people only pass by briefly it may not be a major problem, but on paths with frequent foot traffic or near work waiting areas the line of sight can be blocked during every observation. Distance measurements with an electro-optical distance meter can sometimes be completed quickly, but if someone passes during aiming or verification the measurement work will be interrupted. For safety reasons, tripods or mirrors should not be placed in walkways. It is important not only to ensure line of sight but also to arrange equipment so that it does not obstruct workers’ safe movement.

To make survey points less likely to be obstructed, one effective method is to make good use of site edges and nearby fixed objects. For example, corners of structures, areas near existing fences, easily maintained pavement edges, and stable ground outside the work area can often make it easier to protect survey points. However, if placed too close to a fixed object, that object can block the line of sight from the instrument. Because positions that protect the survey point and positions that ensure line of sight do not necessarily coincide, it is necessary to check both conditions on site.

On sites where terrain and obstacles change as construction progresses, it is important to think about survey point placement in stages. A point that was visible before excavation can end up in the shadow of a step after excavation. As embankment filling or paving advances, previously established survey points may be buried or become inaccessible. Survey points intended for long-term use should be positioned with consideration not only of their current condition but also how they will change a few days later or in the next phase. By keeping the site schedule and the surveying plan together and coordinating when and which survey points will be used, it becomes easier to avoid line-of-sight problems.

To create a layout that makes survey points less likely to be blocked, it is also important to share the meaning of the survey points with everyone on site. Even if only the surveying staff understands the importance of the survey points, other workers may unknowingly place materials on them. Around survey points, it is reassuring to put up markers or protective measures as needed, and to establish a rule to check with the surveying staff if moving or removing them is necessary. However, be careful that the markers or protective materials themselves do not obstruct the line of sight. Protective measures that interfere with surveying would be counterproductive.

Also, placing survey points where they are unlikely to become obstructed during work is useful for site photos and records. If there are prominent fixed features around a survey point and it is a location where the position can be easily described later, it will be less likely to cause confusion during re-surveys or handovers. Conversely, placing a survey point in a spot surrounded by materials or temporary structures can mean it remains in the records but is hard to find on site. Survey point placement is a task that affects not only visibility during observation but also the manageability and reproducibility of the points.

By placing survey points in positions that are unlikely to be blocked during work, observations by the total station are less likely to be interrupted. Because site activity is constantly changing, you should not rely only on the conditions at the time the survey points are placed; instead, it is necessary to position them with foresight for changes in materials, vehicles, personnel, and work sequences. A survey point layout that preserves line of sight becomes effective only when coordinated not just with the surveyor’s ingenuity but also with the overall site planning and sequencing.

Tip 5: Prepare backup points and an arrangement that makes re-observation easy

No matter how carefully you position survey points, line-of-sight problems cannot always be completely avoided on site. Sudden material deliveries, movement of heavy equipment, changes in weather, the erection of temporary structures, or alterations to the construction area often make planned survey points unusable. Therefore, when laying out survey points for a total station, it is important to provide backup points and arrangements that are easy to re-observe from the outset. Simply having a backup strategy can greatly reduce the amount of rework when line-of-sight issues occur.

Backup points do not simply mean adding extra points. It is important to place them where they can achieve the same work objectives in place of a survey point that becomes unusable. For example, consider whether, if a given survey point is obscured by materials, you can verify the same area from a nearby alternate point or re-take a backsight from another instrument station to measure it. When placing backup points, you need to check together the relationship with reference points, the ease of taking backsights, the management of survey point names, the workflow, and safety.

An arrangement that is easy to re-observe refers to a condition in which the same point can be easily rechecked if doubts arise about the survey results. When measurements are unstable or coordinates seem off, a follow-up verification survey may be carried out. If the survey point is located where it is hard to see or difficult to access, re-observation will take more time. Even if the initial observation was possible, an arrangement that cannot be confirmed later leaves quality-control concerns. Survey points should not be treated as a one-time measurement; they should be positioned so they can be rechecked as necessary.

When establishing backup points, it is important to standardize the way point names are assigned and how records are kept. On site, the risk of mix-ups increases as the number of points grows. If it is unclear which points are the original survey points and which are auxiliary when using backup points, organizing the survey data becomes confusing. Point names should be easy to understand on site, and you must ensure that field logs, instrument data, drawings, and photographs can be cross-referenced. This is especially important when multiple people are working; do not rely on verbal communication alone, but keep written records.

When arranging backup points, also anticipate the workflow when the instrument is reset. If visibility is impaired, thinking in advance about where to move the instrument, which backsights will be visible from the new location, and which survey points can be remeasured will speed up on-site decision-making. If you prepare several candidate instrument stations in advance, you can continue work from another position if one location becomes unusable. Because moving the instrument itself takes time when using an electronic total station, preparing candidate relocation points has a significant benefit.

Also, backup points help maintain the continuity of surveying. On long-term sites, the control points initially established may be removed, buried by construction, or become obscured and no longer visible. Even in such cases, having backup or auxiliary points makes it easier to connect the survey control. Of course, points used as control must be handled after performing the necessary checks and accuracy management, but having multiple options is effective for adapting to changing site conditions.

To create a layout that is easy to re-survey, it is also important to record the surroundings of the survey point with photos and notes. Even if the point name alone is hard to find on site, having records of nearby fixed objects, a sense of distance, direction, and landmarks makes it easier to relocate. When taking photos, rather than zooming in only on the survey point, record it so that its position relative to the surroundings is clear, which makes it more practical for field work. However, ensure the recording method follows site rules and take care that personal or unnecessary information is not captured.

Preparing backup points is not meant to complicate the work, but a measure to prepare for uncertainties on site. If you hurriedly add points after visibility deteriorates, verifying survey consistency and organizing records will become time-consuming. By planning backup points and re-observation procedures from the start, you can calmly deal with unexpected obstacles or changes to the work schedule. In arranging survey points for a total station, preparing points that can be used later—not just those visible now—leads to more stable surveying.

Improve Total Station Work Efficiency by Arranging Survey Points to Maintain Line of Sight

To avoid line-of-sight problems with an electronic total station, it's important to think of placing survey points not in "places where you can put them" but in "places where you can keep measuring." First confirm the area visible from the instrument station, choose a position that allows sight to both the backsight and the survey point, consider the survey point's height in anticipation of elevation differences and obstacles, select locations that are unlikely to be blocked during work, and prepare backup points and arrangements that make re-observation easy; by doing so you can reduce rework caused by line-of-sight failures.

The quality of survey point placement affects not only the speed of surveying work but also the ease of verifying measurement results. If you force measurements under poor visibility, the way the mirror is set can become unstable, point names can be mixed up, and backsight verification may be insufficient. Conversely, if you place survey points with visibility in mind, the observation flow stabilizes and it becomes easier to identify the cause when a measurement value feels suspicious.

In practice, site conditions are constantly changing, so things do not always go according to the initial plan. That's precisely why it's important to leave room when arranging survey points. Consider multiple candidates for instrument stations, place them in positions where backsight points are easy to verify, make the surroundings of survey points less likely to be blocked, prepare reserve points, and standardize point names and records. By accumulating these basic measures, it becomes easier to take advantage of a total station's performance in the field.

Also, the placement of survey points is not something that the surveying personnel can complete on their own. By sharing information with people involved on site—construction supervisors, heavy equipment operators, material delivery personnel, mirror operators, and others—the survey points are more likely to be protected and the line of sight maintained. If you share where the survey points are and why those locations are important, you can reduce the risk of them being covered by materials or stepped on in walkways. To improve the work efficiency of a total station, not only surveying skills but also coordination within the site are essential.

When planning the placement of survey points, it's best to start by walking the site and checking the area visible from candidate instrument set-up positions. Based on that, sequentially confirm whether the backsight is visible, whether the survey points can still be used during construction, whether they are not obstructed by differences in elevation, and whether there are alternative measurement methods. If you make these checks routine, you can reduce interruptions and re-measurements caused by poor line of sight and make the overall surveying work proceed more smoothly.

On the other hand, at some sites it can be difficult to rely solely on an optical total station. In locations where maintaining line of sight is difficult, at sites where survey points change frequently, or in situations where a small team needs to verify positions quickly, it can be effective to combine methods such as GNSS surveying, photographic records, electronic field books, and construction management apps according to site conditions. While basing work on precise observations by an optical total station, organizing routine methods for position checks and site records will make it easier to carry out both surveying operations and construction management.