What Are Checkpoints in Drone Mapping? Why We Don't Use Every Ground Control Point for Control

When clients first hear about Ground Control Points (GCPs), they often assume that every surveyed point on a project should be used to improve the accuracy of the final map. While that seems logical, it's actually not the best practice.

One of the most important quality assurance techniques in professional drone mapping is intentionally leaving some surveyed points out of the processing workflow. These points become checkpoints, and they play a critical role in verifying the accuracy of the final deliverables.

At California From Above, checkpoints are an important part of how we evaluate mapping quality before delivering data to our clients.

Verifying and marking ground control point in an open field

What Is a Ground Control Point?

A Ground Control Point (GCP) is a clearly identifiable marker on the ground whose coordinates have been accurately measured using GNSS surveying equipment.

These points help align drone imagery to real-world coordinates during photogrammetric processing. When properly distributed across a project, GCPs significantly improve the absolute accuracy of products such as:

• Orthomosaic maps

• Digital Surface Models (DSMs)

• Dense point clouds

• Contour maps

• Volume calculations

• Cut and fill analysis

What Are Drone Mapping Checkpoints?

A checkpoint is a surveyed point that is not used during image alignment.

Instead, it remains independent throughout processing. Once the project is complete, the software compares the mapped location of the checkpoint with its surveyed coordinates.

The difference between those two positions becomes an independent measurement of project accuracy.

Think of it like taking a test.

If you already know every question and answer beforehand, you can't really judge how well you understand the material. Checkpoints work the same way, they provide an unbiased test of how accurately the model represents the real world.

At California From Above, drone mapping checkpoints are part of our quality assurance process for verifying project accuracy.

Why Not Use Every Point as Control?

Using every surveyed point as a control point can actually hide problems.

If one surveyed point contains an incorrect measurement, or if a target was marked incorrectly during processing, the software may still force the model to fit that bad data.

Without checkpoints, there is no independent way to determine whether the final model is truly accurate.

By leaving several points out as checkpoints, you gain confidence that the finished products accurately represent the site—not just the points used to build the model.

How Checkpoints Help Identify Problems

One of the biggest advantages of checkpoints is their ability to reveal issues before deliverables reach the client.

For example, imagine a project with twelve surveyed points.

You may decide to use nine as Ground Control Points while reserving three as checkpoints.

If two checkpoints agree closely with their surveyed positions but one shows a significantly larger error, that's an indication that something deserves further investigation.

Possible causes could include:

• A poor GNSS observation when the point was surveyed

• A damaged or disturbed control point

• An incorrect target marking during photogrammetric processing

• Local site conditions affecting the measurement

• An issue with the original project control

Without checkpoints, those problems can be much harder to identify.

Why We Place More Control Than the Minimum

Some projects are completed using only the minimum number of control points required.

While that may save time in the field, it reduces flexibility during quality assurance.

Whenever practical, we prefer to establish enough well-distributed control so that one or more points can be reserved as checkpoints.

This approach provides several advantages:

• Independent verification of accuracy

• Greater confidence in deliverables

• The ability to investigate suspect points without compromising project coverage

• Better documentation of project quality

In many cases, having a few additional high-quality control points provides more value than trying to get by with the absolute minimum.

Accuracy Is More Than Just a Number

Modern RTK drones are capable of producing remarkably accurate datasets, but equipment alone doesn't guarantee reliable results.

Professional mapping depends on careful planning, quality field measurements, proper processing, and independent verification.

Checkpoints provide that final layer of confidence.

Rather than simply assuming the project is accurate, they allow us to measure it objectively.

That's one of the reasons they're considered a best practice on professional mapping projects.

Final Thoughts

Drone mapping isn't just about flying a drone, it's about producing dependable spatial data that engineers, contractors, developers, and project managers can trust.

Using independent checkpoints helps verify that confidence before deliverables are released.

At California From Above, we believe quality isn't something you assume. It's something you measure.

Whether we're producing orthomosaics, Digital Surface Models, volume calculations, or construction progress maps, checkpoints are one of the tools that help ensure our clients receive accurate, repeatable results.

Need accurate drone mapping for your next project?

California From Above provides RTK drone mapping, construction progress monitoring, orthomosaics, Digital Surface Models (DSMs), volume calculations, and survey-support deliverables throughout California's Central Valley.

Contact us today to discuss your project.