6 Steps to Verify Deviations from the Design Drawings Using a Total Station

When confirming positions on site using a total station, simply measuring points alone does not allow you to correctly assess discrepancies with the design drawings. If the coordinates on the drawings, the reference points used on site, the setup of the instrument point and backsight point, the instrument height and mirror height, and the method for post-measurement verification are not all consistent, the construction position may appear to be offset even though it is actually correct, or conversely a real offset may be overlooked. Especially when verifying earthworks, roads, structures, exterior works, foundations, grid lines, or pile positions, it is important not only to record the numerical values but also to retain the assumptions under which those values were measured.

This article explains six practical steps that are easy to use on site for field personnel who use an optical total station to check for discrepancies with the design drawings. It is organized as a basic workflow for verifying consistency between the design drawings and the actual site, without relying on specific equipment or software.

Table of Contents

• The approach to initially align when checking for discrepancies with the design drawings

• Step 1: Organize the drawing standards and the items to be checked

• Step 2 Confirm the site reference points and coordinate conditions

• Step 3 Stabilize the installation conditions of the optical distance measuring instrument

• Step 4: Measure the verification points and compare them with the design values

• Step 5: Distinguish the direction and cause of the misalignment

• Step 6 Keep records to inform the next construction decision

• Summary: The verification accuracy of optical surveying instruments varies greatly depending on how the prerequisite conditions are organized.

Initial alignment strategy for checking discrepancies against the design drawings

Checking discrepancies between the design drawings and measurements with a total station may appear to be a simple task of measuring points on site and comparing them to the design values. However, in practice, before comparing measured values with the design you must clarify what reference the drawings are based on, which coordinate system is being used on site, and whether the same assumptions are being used for staking out during construction and for as-built verification. If you begin measuring while these points are unclear, the comparison results will be unstable even if the total station measurements themselves are correct.

Design drawings include various information such as plan position, elevation, grid lines, centerlines, boundary lines, outlines of structures, slope shoulder and slope toe, road centerline, and design elevations. If you try to check everything in the same way, the scope of what you need to verify becomes too broad, making it harder to see the deviations that need to be judged on site. First, it is important to distinguish whether what you are checking this time is the plan position, the elevation, or both.

For example, when checking the alignment (centerline) of a structure, you check whether the centerline on the design drawings matches the positions of the marks or stakes set out on site. Meanwhile, when checking the as-built shape or finished elevation, you look at how much the field survey points differ from the design or planned elevations. On roadworks and land development sites, you may also check simultaneously the offset from the centerline, the lateral position across the cross-section, and differences in elevation. Because the values to be checked differ depending on the item being verified, it is necessary to clarify the purpose before measuring.

A total station measures angles and distances and calculates coordinates based on settings such as the instrument point and the backsight point. Therefore, settings such as the coordinates of the reference points, the coordinates of the instrument point, the direction of the backsight, the instrument height, the mirror height, the prism constant, and the distance-measurement mode affect the results. When checking for discrepancies against design drawings, you need to verify each of these settings one by one and make clear which assumptions the measurement results are based on.

Also, discrepancies with the design drawings do not necessarily mean only construction mistakes. They can arise from various causes such as differences in drawing versions, differences in coordinate transformation conditions, confusion over the reference points used on site, misidentification of survey point numbers, input errors, unstable instrument setup, sighting errors, or incorrect mirror height input. Therefore, when a discrepancy is found, it is important not to immediately suspect construction, but to check the surveying conditions and the design conditions in sequence.

A practical approach for on-site work is to first standardize the conditions on the drawing side, then align the reference standards on the site side, after that verify the total station's settings and measurement methods, and finally assess the results. By following this sequence, differences in judgment among operators are reduced and it becomes easier to explain discrepancies with the drawings.

Step 1 Organize the reference standards and items to be checked for the design drawings

The first step is to organize which information on the design drawings will be used as the reference for checking deviations. On site, multiple documents may be used, such as plan drawings, longitudinal profiles, cross sections, structural drawings, detail drawings, coordinate lists, control point results, and construction drawings. The more documents there are, the easier it is for it to become unclear which drawing is being treated as the authoritative one for the work. Deciding in advance what to check and which drawings to reference before measuring with the total station will make post-measurement verification smoother.

The first thing to confirm is whether the location information shown on the design drawings is managed as coordinates or as dimensions and distances from grid lines. If a coordinate list exists, verify that the survey point name, X coordinate, Y coordinate, elevation, and notes match the on-site data. If it is managed by dimensions, clarify the reference grid lines, centerlines, boundary lines, corners of structures, existing elements, etc., and organize what to check, from where and in which direction.

Next, check the drawing revision and change history. On site, original drawings, revised drawings, construction approval drawings, and drawings after on-site adjustments may coexist. If you verify design values based on old drawings, even if the on-site position measured with a total station is correct, discrepancies will appear in the comparison results. In particular, positions of structures after changes, design elevations, road widths, locations of gutters and curbs, and the alignment of retaining walls may be altered by drawing updates. Before surveying, confirm whether the design drawings to be used are the revision that has been checked on site.

Decide specifically what will be checked. For example, whether you are verifying pile positions, grid lines or centerlines, corners of structures, or the elevation of the excavation bottom or finished surfaces will change how you select measurement points. If you work on site with a feeling of “I’ll just measure around here,” the points you compare to the design values will become misaligned. The basic rule for checking for discrepancies is to establish a one-to-one correspondence between points on the design drawings and the points measured in the field.

When verifying measurements that include elevation, attention must be paid to the treatment of reference elevations and bench marks. Confirm which elevation datum the planned elevations shown on the design drawings are based on, and make them consistent with the elevation datum used on site. Even if the horizontal positions match, differences in elevation datum can affect the as‑built condition and construction decisions. When checking elevations with a total station, inputs such as instrument height and prism height are also involved, so the elevation conditions on the design drawings should be clarified in advance.

At this stage, it is important to organize the design values before inputting them into the total station. When creating a list of design coordinates and checkpoints, including the point name, verification details, design coordinates, design elevation, reference drawings, and verification date will reduce confusion on site. If point names are similar or the same numbers are used in different areas, managing them with the construction area or section name included will prevent mix-ups.

If measurements are taken without clarifying the reference standards in the design drawings, it becomes difficult to later explain the meaning of the values obtained on site. Conversely, if the conditions of the drawings are aligned in advance, it becomes easier to determine whether discrepancies on site are due to construction issues or to problems with the drawings or data. To make the most of the accuracy of the total station, it is important at the initial stage to reduce misreading of the drawings and mix-ups of data.

Step 2 Confirm on-site reference points and coordinate conditions

The next step is to verify the reference points and coordinate conditions used on site. The total station determines direction and position based on the instrument station and the backsight. Therefore, if the coordinates of the reference points or the backsight direction are incorrect, all subsequently measured points will be affected. When checking for discrepancies with the design drawings, it is essential to confirm not only the points being measured but also the reliability of the reference points that support those measurements.

First, verify that the reference points to be used are appropriate for the current construction and survey scope. On site, existing reference points, temporary construction control points, tie-in points, auxiliary points, and points set during previous work may coexist. Do not judge by appearance alone; check the point names, coordinates, installation locations, and usage history, and confirm that they correspond to the design drawings and survey results. Be careful, because when point names are similar or stakes and pins are in close proximity, mix-ups can easily occur.

Also check the physical condition of the control point. If the stake has moved, a marker bolt or pin is protruding, surrounding pavement or soil has settled, it has been affected by heavy machinery or vehicles, or its relative position has changed due to removal of temporary structures or fill, the coordinate values may be correct but its reliability as the actual point is reduced. Before using a control point, observe the surrounding conditions and, if necessary, cross-check it with another control point or a known point.

When checking coordinate conditions, you verify whether the coordinate system on the design drawings matches the coordinate system used on site. The way coordinates are managed varies by site: coordinates used for public surveys, local coordinates for construction, arbitrary-origin coordinates, coordinates converted for construction, and so on. If you compare design values and measured values while the coordinate systems differ, the whole set may appear shifted in a consistent direction. In particular, when using design coordinates converted from another survey dataset, it is important to confirm that conditions such as the origin, orientation, scale, rotation, and translation are properly defined.

Selection of the backsight point also has a major impact on the results. The backsight point is the reference used to determine the orientation of the instrument. If the distance to the backsight point is too short or if it is located somewhere that is difficult to sight, even a slight sighting error can easily affect the check points. Depending on site conditions, it may be necessary to choose the backsight from multiple candidates and decide based on line of sight, distance, stability, and the relationship with the work area. Mistaking the backsight point or making errors when inputting coordinates can appear as discrepancies with the design drawings, so checks before starting work are essential.

Also, checking the consistency between reference points makes later decisions easier. After setting up the instrument point, measure known points and check points other than the backsight, and verify whether the coordinate differences and elevation differences fall within an acceptable range. Because acceptable ranges vary depending on the type of work and management standards, judge according to the site’s criteria. If large discrepancies appear here, before proceeding to verify the measurement target you need to review the reference points, instrument setup, backsight configuration, and input data.

The purpose of checking the site's reference points and coordinate conditions is to ensure the reliability of the measurements themselves. If you do not confirm that the site references are correct before discussing discrepancies with the design drawings, you may misidentify the cause of the discrepancy. When verifying with a total station, rather than only pursuing measurement points, first establishing the consistency of the references will ultimately shorten the time required for the work.

Procedure 3 Stabilize the setup conditions of the total station

After checking the drawings and the reference point conditions, stabilize the installation conditions of the total station. The total station is a precision measuring instrument, but if the on-site setup or input conditions are unstable, the measurement results will be affected. When checking for discrepancies against the drawings, it is important to verify the instrument’s installation state before judging differences in the measured target.

First, set up the tripod on stable ground. Soft soil, the edge of an embankment, locations subject to vehicle vibration, areas where workers frequently pass, and places near temporary structures can cause the tripod to move during measurements. Firmly secure the tripod legs to the ground, and be aware that even if you think you have compacted the ground, it may settle over time or because of vibration. On paved or concrete surfaces, also be careful of slipping. Even slight movement of the instrument can appear as a large discrepancy at distant reference points.

Next, carefully perform centering and leveling. Setting the instrument correctly directly over the instrument point and checking the bubble level or electronic leveling display to keep it level are fundamentals of a total station. Check the leveling not only immediately after setup but also during measurements as needed. Long periods of work, temperature changes, slight ground movement, or contact with the tripod can alter the setup. When checking for discrepancies with the design drawings, rechecking known points before and after measurement makes it easier to determine whether the instrument has moved.

Measuring and entering instrument height is also important. When checks include height, errors in instrument height entry will appear directly as height differences. Instrument height should be measured from the instrument point’s mark or the reference surface to the instrument’s designated position, but if the measurement location or the way of reading are not standardized among operators, discrepancies are likely to occur. Making it routine to standardize how tape measures or measuring tools are positioned, the reading units, recording in notes, and verification after entry can reduce instrument height errors.

Also check mirror height and reflector conditions. When using a prism, verify that the mirror height matches the actual height set in the field and the value entered into the instrument. Misreading the pole graduations or forgetting to update the input after changing the height can affect not only the plan position but also height verification. When using reflective sheets or non-prism measurements, confirm the position of the measured surface, its reflective condition, and the choice of distance-measurement mode, and ensure that the point on the design drawings corresponds to the point being measured on site.

Checking the prism constant and the ranging mode is also essential. If the conditions of the reflector being used and the instrument settings do not match, a consistent difference in distance can occur. At sites where multiple reflectors are used interchangeably, confirm that the settings have not changed during work. In non-prism measurements, because the instrument can pick up another reflector behind or in front of the surface you want to measure, take measurements while observing the shape of the target and the surrounding conditions.

After setting the backsight, measure known points and check points to perform an initial verification. Rather than starting work just because the instrument point and backsight have been set, measure another known point to confirm that the horizontal position and elevation are as expected. If a large discrepancy appears here, there may be a problem with one of the following: the instrument point coordinates, the backsight coordinates, the backsight direction, the instrument height, the mirror height, the prism constant, or the distance-measurement mode. Eliminating the cause before proceeding to measure the check points prevents having to redo work.

Installation conditions for an optical total station are the foundation of measurement results. To correctly verify deviations from the design drawings, on-site installation, data input, reflector conditions, and backsight checks must be treated as a single continuous workflow. Rather than relying solely on the instrument's performance, careful installation and verification enhance the explanatory power of the measurement results.

Step 4 Measure the verification points and compare them with the design values

Once installation conditions are in place, measure the points to be checked and compare them against the design values. At this stage, rather than simply increasing the number of measurements, it is important to select points that clearly correspond to the drawings and to compare the measurement results under the same conditions. Listing numbers for points whose meaning is ambiguous makes it difficult to judge discrepancies.

When selecting points to verify, prioritize points on the design drawings that are important for management. For structures, these include corners, grid lines, centerlines, ends, openings, foundation centers, and anchor locations. For roads and land development, points to check include the center point, carriageway edge, shoulder, slope toe, side ditch locations, curb positions, and representative points of the planned surface. For as-built verification, measure points corresponding to the design elevation and planned elevation, and decide in advance whether to prioritize horizontal position or elevation.

During measurement, clarify which point on the drawings corresponds to the point being measured on site. For example, when measuring a corner of a structure, the position will differ depending on whether it is the corner of the finished surface, the corner of the formwork, the intersection of layout lines, or the center of a pile. If the location where a pole is set differs by a few centimeters (a few in), it may appear as a discrepancy with the drawings. When the measurer and the recorder are different people, calling out and confirming the point name and what is being checked while working can reduce mix-ups.

Measurement results are organized as differences from the design values. For planar positions, viewing the differences in the X and Y directions, or as longitudinal and transverse differences, makes the direction of the displacement easier to understand. For elevation, clarify whether it is higher or lower than the design elevation. If you look only at the magnitude of the difference, it becomes difficult to determine which way to adjust, so it is important to record the direction as well.

When reconciling, pay attention to the decimal places and rounding of measured and design values. If the number of displayed digits differs between design data, field notes, instrument readouts, and reports, the perceived differences may change. Compare using the number of digits specified by management standards, and avoid judging solely on overly detailed displays. However, because rounding can cause actual differences to be overlooked, it is prudent to distinguish the original measured values from the processed (rounded) values according to the site's management practices.

When measuring multiple points, the order of measurement is also important. First check the points closest to the reference, then measure the edges of the work area and other critical locations to get a sense of the overall trend. If the measurement area is large, periodically recheck the backsight and known points to see whether the instrument has moved. If you only notice an instrument shift after measuring all the checkpoints, you may need to redo the measurements.

When comparing with design values, it is also important not to make a judgment based on a single point. If only one point is significantly displaced, review the measurement location of that point, the point name, how the pole was set up, the field marks, and the corresponding point on the design drawings. If multiple points are shifted by a similar amount in the same direction, the cause may lie in the reference points, the coordinate system, the backsight direction, or the conversion conditions of the design data. If there is large variability between individual points, the cause may be the construction conditions, the measurement methods, or how points were taken on site.

The measurement results from a total station serve as material for on-site decision-making. By checking the results on the spot and, if necessary, re-measuring or cross-checking from other points, you can reduce rework later. Rather than stopping at simply measuring, the central task of deviation checking is to compare the findings with the design drawings and organize how large the differences are and in which directions they occur.

Step 5 Isolate the direction and cause of the deviation

If measurement results differ, identify the direction of the deviation and isolate its cause. When a discrepancy with the design drawings is found, you may be tempted to immediately correct the construction position, but before doing so you must confirm whether the deviation is actually due to the construction work or caused by surveying conditions or design data. If you make corrections without isolating the cause, you risk moving away from the correct position.

The first thing to check is whether the offset occurs at a single point or shows the same pattern across multiple points. If it is an offset at only one point, possible causes include confusing measurement points, a shift in the pole position, an input error in the measurement-point number, misreading the on-site display, or a mismatch in the corresponding point on the design drawing. If multiple points are shifted in the same direction, suspect factors that affect the whole system, such as the coordinate system, reference points, the backsight, or the transformation conditions of the design data.

Next, check the direction of the displacement. When viewed as differences in the X and Y directions, determine whether it is shifted by a constant amount in a particular direction, shifted as if rotated, or whether the difference increases with distance. If it is shifted by the same amount in a fixed direction, it may be due to a mix-up of the origin or reference point, or differences in the translation settings of the design data. If the difference grows as distance increases, it may be related to the backsight direction, the rotation parameters of the coordinate transformation, or the orientation of the reference line.

When assessing height discrepancies, determine whether the entire set is uniformly higher or lower, or whether there are point-by-point variations. If the whole set is shifted by a constant amount, check the instrument height, mirror height, reference height, benchmark, and the handling of design elevation. If there are point-by-point variations, review the on-site finish condition, how the pole is erected, the choice of measurement surface, irregularities of the measured object, and the condition during construction. When confirming elevations, even if the horizontal position is correct, differences can arise if the pole’s installation position or the surface being measured differs, so it is important to verify together with the on-site conditions.

We also review the surveying conditions. We check whether the instrument station has moved, whether the backsight has been properly sighted, whether any discrepancy appears at the check point after the backsight, whether the instrument height and mirror height inputs are correct, and whether the prism constant and distance-measurement mode match the reflector being used. In particular, when the pole height is changed during work or the reflector is switched, it is easy to omit updating the inputs.

The design data also needs to be checked. Verify that the drawing revision is correct, the coordinate list is up to date, the construction area and work section have not been mixed up, survey point numbers are not duplicated, and that the calculation parameters used to generate coordinates from the drawing dimensions are correct. If the dimensions on the design drawings do not match the coordinate data, or if there are input errors in the construction data prepared on site, these will also appear as discrepancies with the total station measurements.

When checking construction conditions, you verify whether points on site indicate the positions intended on the drawings. Temporary stakes, offset stakes, reference marks, formwork, rebar, excavation faces, and finished surfaces have different meanings depending on the construction stage. If temporary markers are mistakenly measured as the final positions, or the outer face of formwork is treated as the center of the structure, you can misjudge deviations. On site, it is necessary to make clear whether the surveyed point is the finished form or a control point during construction.

When isolating causes, re-measurement is also effective. Measuring the same point again, checking a different known point, measuring from another instrument station, or establishing an auxiliary point near the object being checked and rechecking—looking at results by multiple methods makes it easier to narrow down the cause. However, simply repeating measurements may not reveal the cause. It is important to check measurement conditions, design conditions, and site conditions separately.

Isolating discrepancies is a preliminary step before making construction decisions. Instead of deciding based only on the fact that a total station has shown a discrepancy, clarifying the direction, the points, and the conditions under which that discrepancy occurs makes it clear what should be corrected. This helps prevent unnecessary rework and incorrect corrective actions.

Step 6 Keep records and use them to inform the next construction decisions

The final step is to record the measurement results and the judgments made, and to use them to inform the next construction decisions. Even if you check for discrepancies with the design drawings using a total station, insufficient records will make it difficult to explain the results later or to recheck them. It is important to record not only the measured values but also the conditions under which they were measured, which design drawings were referenced, and which points were checked.

As for what to record, the basics are the measurement date, the operator, the instrument station used, the backsight, the reference control points checked, the design drawings referenced, the names of the points checked, the design values, the measured values, the differences, and the decisions made. If heights were checked, also record the instrument height, the mirror height, the height reference, and the condition of the measured surface, as this makes it easier to trace causes later. If a reflector or the distance-measurement mode was changed, record those conditions as well.

Photos and site notes are also useful. Taking photos that show the positions of measurement points, where poles were set up, site landmarks, surrounding conditions, and the condition of the items being checked can supplement information that is hard to understand from numbers alone. In particular, during inspections carried out in the middle of construction, the condition at the time of measurement may change later. For areas that will become hidden as work progresses—excavation, formwork, rebar, paving, embankment, backfilling, etc.—it is important to keep measurement records together with photos.

If a discrepancy is likely to become a management issue, we also record the decision-making process. For example, if a difference appeared in the initial measurement, we note that we rechecked the reference point, reviewed the backsight, remeasured from a different instrument point, checked the drawing revision, and confirmed the meaning of the on-site points with the construction supervisor. This way, the record shows not just that there was a discrepancy, but how it was verified and how the decision was reached.

The format of records should be easy to use continuously on site. Record formats that are too complex will not be maintained in a busy site. On the other hand, records that are too simple—containing only point names, design values, and measured values—make it difficult to recreate the situation later. By arranging the format to match the site’s management standards so that the necessary information is preserved without omission or redundancy, verification work becomes more stable.

To link measurement results to subsequent construction decisions, it is also important to express them in a way that anyone can understand. For example, rather than simply writing "misalignment," record which point, relative to the design value, in which direction, and by how much it differs. If correction is necessary, record which task will perform the correction, when the recheck will be carried out, and whether it has been shared with the relevant parties. Even when you determine that no correction is needed, recording the rationale will make it easier to explain later.

Also, accumulating measurement results makes it easier to identify trends within the same site. If you can see patterns—such as consistent differences in the same direction within a particular area, height variations that tend to occur during a specific work process, or instability when checking with a particular reference point—those insights can lead to improvements in future work. Measurements taken with a total station are useful not only for on-the-spot verification but also for overall quality control of the site.

The purpose of keeping records is not to assign blame but to ensure sound on-site decision-making. Discrepancies with the design drawings can arise from a combination of construction, surveying, design data, and site conditions. That is why it is important to record measurement results and the conditions under which they were checked, so that all stakeholders can make decisions based on the same information.

Summary: The verification accuracy of EDM instruments varies greatly depending on how the preconditions are organized

To check discrepancies with the design drawings using a total station, you need to manage the entire workflow—not only the measurement work but also the drawings, reference points, coordinate conditions, instrument setup, comparison methods, and recordkeeping. Even if the measured values are accurate, if the drawing revision is different, the reference points have been mistaken, or the instrument height or mirror height has been entered incorrectly, the comparison results cannot be correctly evaluated.

What matters in practice is first organizing the reference information and the items to be verified on the design drawings, and then confirming the site reference points and coordinate conditions. After that, set up the total station securely and confirm the instrument height, prism height, backsight point, and reflector conditions before beginning measurements. After measuring, organize the differences from the design values by direction and magnitude, and determine whether the discrepancy is isolated to a single point or represents an overall trend. Perform re-measurements or checks at other points as needed, isolate the cause, and use that information to inform construction decisions.

Verification of discrepancies with the design drawings is an important task for maintaining on-site quality. The purpose is not merely to find deviations, but to correctly determine their causes and connect the necessary corrections and checks to subsequent work.

Field personnel using a total station need to organize their work to include not only instrument operation but also reading the design drawings, understanding coordinate conditions, and methods of record-keeping.

In recent years, operations have required promptly verifying position information obtained on site and linking it to recording and sharing. While using traditional total station checks as a foundation, combining survey data management tools, photo records, report creation, and on-site sharing mechanisms as needed makes it easier to communicate verification results to stakeholders. To stabilize checks for deviations from design drawings, it is important for the entire site to thoroughly enforce not only the accuracy of equipment but also the clarification of assumptions, the standardization of measurement procedures, and the continuity of record keeping.