Check Point

Definition

A check point is a surveying station established at a location with known or previously determined coordinates that serves as a reference for verifying the accuracy of measurements, calculations, and surveying instruments. Check points are essential quality control mechanisms in surveying practice.

Purpose and Importance

Check points fulfill several critical functions in surveying operations:

Accuracy Verification: They allow surveyors to compare measured values against established benchmarks to detect errors and discrepancies.

Instrument Calibration: Check points help identify systematic errors in surveying equipment that may require adjustment or replacement.

Quality Assurance: They provide independent verification of survey work quality and reliability.

Error Detection: Check points can reveal computational mistakes, procedural errors, or environmental factors affecting measurements.

Types of Check Points

Permanent Check Points

These are established at fixed locations with coordinates documented in official records. They remain available for future surveys and are often marked with monuments or permanent markers.

Temporary Check Points

Temporary check points are established for specific projects and may be removed after survey completion. They are typically marked with stakes, paint, or temporary monuments.

Control Check Points

Points established from high-order control networks that provide reliable reference positions for lower-order surveys.

Establishment and Selection

Effective check points should be:

Accessible: Located where surveyors can easily reach and observe them

Stable: Positioned on firm ground unlikely to shift or settle

Visible: Clearly marked and identifiable in the field

Well-distributed: Strategically placed throughout the survey area

Documented: Recorded with accurate coordinates and descriptions

Applications in Surveying

Leveling Operations

Check points verify height measurements and identify cumulative errors in differential leveling runs. Surveyors typically establish check points at intervals along level lines.

Traverse Surveys

In traverse surveying, check points verify angle and distance measurements, ensuring the traverse closes properly and meets accuracy standards.

GPS/GNSS Surveys

Check points validate the accuracy of satellite-based positioning, particularly important when transitioning between different datum or coordinate systems.

Photogrammetry

Check points ground-truth aerial or drone imagery and ensure proper georeferencing and scale accuracy.

Quality Control Procedures

Proper check point procedures include:

1. Planning: Identify check point locations before fieldwork begins 2. Establishment: Carefully set and document check points with precise coordinates 3. Measurement: Independently measure from check points using appropriate methods 4. Comparison: Compare measured values to established coordinates 5. Analysis: Investigate discrepancies exceeding acceptable tolerances 6. Documentation: Record all check point measurements and results

Acceptable Tolerances

Acceptable discrepancies between measured and established values depend on:

Survey accuracy requirements and project specifications

Type of surveying equipment used

Terrain and environmental conditions

Professional standards and regulations

Typical tolerance standards range from millimeters for precise engineering surveys to centimeters for general mapping surveys.

Conclusion

Check points represent a fundamental quality assurance component in surveying practice. By providing independent verification of measurements and equipment performance, they ensure survey data meets required accuracy standards and maintains professional reliability. Proper establishment, documentation, and use of check points significantly enhances survey credibility and client confidence in surveying results.