Check Point in Surveying

Definition

A check point is a predetermined survey station or reference location established during surveying operations to verify the accuracy and integrity of survey measurements, calculations, and field procedures. It serves as an independent verification mechanism to detect errors in data collection and processing.

Purpose and Function

Check points play a critical role in quality assurance within surveying operations. They are strategically selected points whose positions or elevations have been previously determined with high accuracy through independent methods. During survey work, measurements are taken to these check points and compared against their known values. Significant discrepancies indicate potential errors in the survey process that require investigation and correction.

Types of Check Points

Control Check Points

These are established points of known horizontal and vertical position, typically derived from higher-order surveys or benchmark networks. They provide absolute reference standards for verification.

Intermediate Check Points

Temporary points established during a survey project to check measurements between primary control stations. These are often used in linear surveys such as traverses or level lines.

Closure Check Points

Points used to verify the closure of a survey loop or traverse. The surveyor returns to the starting point and compares the measured position with the original known position.

Implementation Procedures

When establishing check points, surveyors should:

1. Select appropriate locations - Choose points that are accessible and clearly visible from survey stations 2. Establish independent verification - Use alternative survey methods to determine known positions 3. Document thoroughly - Record all measurements and calculations for check point verification 4. Analyze discrepancies - Compare field measurements against known values and investigate significant differences 5. Apply corrections - Adjust survey data if errors are identified and systematic corrections can be determined

Tolerance Standards

Acceptable discrepancies between measured and known check point positions depend on survey grade and purpose:

High-precision surveys: Tolerance may be ±5mm or less

Engineering surveys: Typically ±20-50mm

Cadastral surveys: Usually ±50-100mm depending on jurisdiction

Reconnaissance surveys: May permit larger tolerances

Advantages

Check points provide several benefits to surveying operations:

Error detection: Identifies systematic and random errors before data acceptance

Quality assurance: Demonstrates compliance with accuracy standards

Confidence building: Increases confidence in final survey results

Cost efficiency: Prevents propagation of errors to subsequent project phases

Professional validation: Meets industry standards and client requirements

Modern Applications

In contemporary surveying, check points are used with:

GPS/GNSS systems: Verifying satellite-derived positions against ground control

Total stations: Checking traverse and triangulation measurements

Level surveys: Verifying height measurements through independent benchmarks

Laser scanning: Validating point cloud accuracy against known reference points

Aerial surveys: Checking photogrammetric measurements against ground control points

Best Practices

Surveyors should establish check points at appropriate intervals—typically every 5-10 stations or every 500-1000 meters in linear surveys. The number and frequency of check points should increase for higher-precision work or challenging environments.

Check points must be marked clearly and their positions carefully documented for future reference. In long-term projects, permanent markers ensure check point availability for subsequent phases.

Conclusion

Check points are essential components of professional surveying practice, providing independent verification of survey accuracy. Their strategic use ensures reliable data for engineering design, construction, and legal applications.