Check Point

Definition

A check point is a surveying station whose position has been previously determined with high accuracy and is used during surveying operations to verify the correctness of measurements, calculations, and instrument performance. Check points serve as reference locations that allow surveyors to assess the quality and reliability of their work in real-time.

Purpose and Function

Check points fulfill several critical functions in surveying practice:

Accuracy Verification

Check points provide independent verification of survey measurements. By measuring from the survey work back to established check points, surveyors can confirm that their data collection methods are producing accurate results. Discrepancies between expected and measured values indicate potential errors requiring investigation.

Quality Control

Regular checks against established points ensure that instrument drift, operator error, or environmental factors have not compromised measurement quality. This continuous quality assurance protects the integrity of the entire survey.

Error Detection

Check points help identify systematic errors in measurements, calculations, or instrument calibration that might otherwise go unnoticed until late stages of the project.

Establishment and Selection

Check points are typically established using high-precision methods such as:

GPS/GNSS surveys with post-processing and multiple occupations

High-order traverse methods using precision instruments

Previously monumented control points from government surveys or prior projects

Third-party verification by independent surveyors

Effective check point selection requires:

1. Accessibility - Points must be reachable without excessive difficulty 2. Visibility - Clear lines of sight for optical measurements 3. Stability - Monuments must remain undisturbed during the survey 4. Distribution - Appropriate spacing throughout the survey area 5. Independence - Should not be derived from the primary survey network

Implementation

Surveyors incorporate check points into their work through:

Intermediate Checks

Measurements are taken to check points during regular survey operations, typically at intervals based on project specifications and risk assessment.

Closure Analysis

After completing survey loops or traverses, measurements are compared to check point coordinates to evaluate closure and determine if adjustments are necessary.

Statistical Evaluation

Errors between observed and known coordinates are analyzed statistically to assess whether they fall within acceptable tolerances defined by project standards.

Standards and Tolerances

Acceptable discrepancies vary based on:

Survey type and purpose

Required accuracy standards

Instrument precision

Distance from check point

Environmental conditions

Most surveying standards specify maximum allowable errors, often expressed as functions of distance or as fixed tolerances.

Importance in Modern Surveying

Check points remain essential despite advances in technology. While modern instruments provide high accuracy, they are subject to systematic errors and equipment malfunctions. Check points provide objective evidence of work quality and are required by most professional standards and client specifications.

In digital surveying workflows, check point measurements are automatically compared to expected values, allowing immediate feedback to field crews.

Conclusion

Check points represent a fundamental quality control mechanism in surveying. Their proper establishment, selection, and use throughout survey operations ensure that measurements meet accuracy requirements and that any problems are detected promptly. Professional surveyors recognize check points as essential rather than optional components of rigorous surveying practice.