Composite True Position Calculator

Enter Coordinates

Units mm in

Use the same units for all inputs.

Tolerance (diametral)

Pass if 2×sqrt(dX² + dY²) ≤ tolerance.

Add Point Row

Point ID	Nominal X	Nominal Y	Actual X	Actual Y	Remove
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Calculate Load Example Data Reset

Use this for anchor bolts, embeds, sleeves, grids, and layout points.

Example Data Table

Formula Used

For each point, compute coordinate deltas:

• dX = ActualX − NominalX
• dY = ActualY − NominalY

Radial position error (distance in the plane):

Radial = √(dX² + dY²)

Diametral true position (common tolerance-zone diameter form):

Diametral = 2 × Radial

Composite reporting uses the pattern’s worst-case (maximum) diametral value, plus helpful statistics such as average and RMS radial deviation.

How to Use

1. Select units and enter a diametral tolerance.
2. Enter nominal design coordinates for each layout point.
3. Enter measured coordinates from total station or as-built survey.
4. Press Calculate to view per-point and composite results.
5. Download CSV or PDF to share with QA/QC teams.

Professional Article

1) Why composite true position matters

Composite true position summarizes how a full pattern of points behaves, not only one point. This prevents fit-up issues when base plates, anchor bolts, embeds, sleeves, and dowels must align across the same footprint. One outlier can stop installation.

2) Typical data sources in construction

Inputs usually come from layout drawings and as-built survey files. Nominal coordinates come from the design grid, while actual coordinates come from a total station or laser tracker. Record the same datum, station setup, and coordinate system for both datasets.

3) Units, datum, and coordinate consistency

Mixing units or datums is a common cause of misleading results. If drawings use millimeters, keep field data in millimeters, and avoid rounding until reporting. Ensure X and Y axes match the project convention, and apply any rotation or translation consistently.

4) Understanding the tolerance input

This calculator compares a diametral tolerance against each point’s diametral true position. Many specs state tolerances like 3 mm, 6 mm, or 10 mm depending on element type and trade. Use the value written on the plan or quality document, and keep it in the selected units before accepting any measured set.

5) Reading per-point deviations

For each point, dX and dY show directional offsets from nominal. The radial value is the straight-line distance in the plane, while the diametral value doubles that distance for a diameter-style zone. Points that exceed the tolerance are flagged, helping crews target corrections efficiently.

6) Composite reporting and worst-case control

Composite assessment focuses on the worst-case point in the set, because that point often controls assembly. The summary also shows the average and RMS radial deviation, which help separate a single bad anchor from a broader drift. Use worst-case for acceptance, and stats for troubleshooting.

7) Practical use cases and sample numbers

Common applications include anchor bolt templates, facade bracket lines, equipment pads, and sleeve groups through slabs. For example, if an anchor’s dX is 1.2 mm and dY is −0.8 mm, the radial is about 1.44 mm and the diametral is about 2.88 mm. These values support quick go/no-go decisions and prefabrication checks.

8) Documentation, handover, and quality control

Exporting a CSV or PDF creates a traceable record for QA/QC and client review. Include tolerance, units, survey date, and crew notes alongside the report. If a point fails, re-measure after correction and attach both reports to show closure.

FAQs

1) What is “composite” true position?

It evaluates a group of points as one pattern, highlighting the worst-case point and overall spread, instead of judging each point in isolation.

2) Why does the calculator use diametral value?

Many construction and fabrication specs express true position as a tolerance-zone diameter, so the calculator reports diametral = 2 × radial.

3) Can I use this for Z/elevation errors?

This tool is 2D (X–Y) for plan position. For elevation, compute a separate Z deviation report or use a 3D positional tolerance workflow.

4) What if my drawing uses a different origin?

Translate or transform one dataset so nominal and actual coordinates share the same origin, axes, and rotation before calculating true position.

5) How many points should I include?

Include all points that must fit together for the same component or assembly, such as an anchor group, bolt pattern, or bracket line.

6) What does RMS radial tell me?

RMS radial indicates typical scatter. A high RMS suggests widespread drift, while a low RMS with one large max often indicates a single outlier.

7) Which export should I use?

Use CSV for spreadsheets and filtering, and PDF for site submittals, field packets, and client sign-off records.