Ground Control points are significant in surveying, mapping, and LiDAR projects. They help link digital data to physical sites, making the results more accurate and trustworthy. Nevertheless, there are no easy ways to use GCPs. There are various challenges in many projects that may compromise data quality if not addressed appropriately.

This article describes the most common issues with ground control points and, more importantly, how to address them effectively.

Difficulty Choosing the Right Locations

The location of the ground control points targets is a major issue. A poor location may make the points less accurate, even when they have been measured correctly.

Common placement issues are:

• Areas that are covered by trees or structures.

• Uneven or sloped surfaces

• Movement/activity areas- areas with high mobility.

• Hard to detect spots in the aerial data.

How to overcome it:

Select open spaces, flat areas, and stable areas. GCPs must be visible in the air and should not be in shadow or near objects. Planning the layout before fieldwork saves time and yields better results.

Limited Visibility in Data Collection

There are cases where ground control points are positioned correctly but are not visible in the information. This tends to occur in regions with heavy vegetation, low light, or a complex sky.

The GCP becomes useless when it is difficult to identify, so it will not be used in data processing.

How to overcome it:

High-contrast, ground-compatible targets should be used. Bright colors, checkboards, or reflective materials are used to ensure things can be seen. It is important to always check visibility before commencing the actual survey.

Inaccurate Coordinate Measurement

A GCP may create issues even when it is placed in the correct location, and the coordinates are measured correctly. Even minor mistakes in the process of acquiring GPS or GNSS measurements will cause misalignment of the whole dataset.

Common causes include:

• Weak satellite signals

• Hurrying with the measuring process.

• Poor equipment calibration

How to overcome it:

Allow time to get the correct GPS location and have the equipment calibrated. Measurements should be rechecked whenever there is an opportunity to minimize the risk of error.

Using Too Few Ground Control Points

The other common difficulty is using too few GCPs. This is usually done to save time or minimise the fieldwork. Regrettably, accuracy can be undermined by fewer points, particularly in large or irregular areas.

Errors are distributed throughout the project space, with a few points of control.

How to overcome it:

The larger the project and the more complex the area, the more GCPs are required. The points are evenly distributed, which gives greater control and more dependable results.

Poor Distribution Across the Site

The availability of sufficient GCPs is critical, and their location is equally essential. When the concentration of points is concentrated in a single area, the rest of the site may lack accuracy.

Lack of even distribution is likely to cause:

• Warping in data

• Inconsistent elevations

• Less confidence in the results.

How to overcome it:

Place the points of the spread ground control at equal distances throughout the entire survey area, at corners and edges. This promotes harmonized control and enhances overall harmony.

Environmental and Weather Challenges

Weather conditions may impact GCP. Targets can move due to rain, wind, or dust, or visibility can decrease. Targets can also be damaged or relocated at any time.

Fieldwork is often subject to unexpected problems arising from environmental factors.

How to overcome it:

Permanently fix targets on the ground and check them prior to the collection of data. You should survey stable weather conditions and re-check the targets when the weather changes.

Data Processing and Matching Issues

The data processing itself may present issues even in the correct placement and measurement of GCPs. Confusion and inaccuracy in pointing, or in matching points to the wrong locations, might occur.

This is one of the steps that is just as important as the field setup, which is usually ignored.

How to overcome it:

Keep accurate records of all GCP sites and consistently identify them. Close matching in the process is ensured to ensure that the control points serve their purpose.

Final Thoughts

Ground control points are basic items, but they must be handled with care. The majority of the challenges arise from poor planning or a lack of attention to detail. These problems can be prevented by selecting suitable sites, making accurate measurements, and ensuring proper distribution.

When used correctly, ground control points enhance data precision and enable much more accurate surveying and LiDAR results.

FAQs

What is the most popular error in the use of ground control points?

The most frequent problems include poor placement and inaccurate measurements, which may be attributed to hasty fieldwork or insufficient planning.

Is it possible to correct the errors of ground control points in processing?

Small problems are fixable, whereas larger placement or measurement issues typically require rearranging or a re-survey.