GCP vs Check Point for Drone Survey – What Is the Difference? Malaysia

GCP vs Check Point for Drone Survey – What Is the Difference? Malaysia

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GCP vs Check Point for Drone Survey Malaysia

Ground Control Point vs Check Point Explained for UAV Mapping & Photogrammetry

When carrying out a drone survey, two terms are often confused:

Ground Control Point (GCP)

and

Check Point (CP)

They may use exactly the same physical target on the ground, and both may be surveyed using GNSS/RTK or Total Station.

But they perform different jobs in the photogrammetry workflow.

QUICK ANSWER: A GCP is normally used to control or constrain the photogrammetric model, while a Check Point is normally kept independent from the adjustment and used to evaluate the accuracy of the finished result.

GCP = CONTROL

CHECK POINT = VERIFY

Understanding this difference is important for professional drone mapping.

What Is a Ground Control Point (GCP)?

A Ground Control Point is a clearly identifiable physical point whose real-world coordinates have been accurately established.

Before the drone flight, the target is positioned on the ground and its reference position is surveyed.

During photogrammetric processing, the corresponding point is identified in the aerial photographs.

Its known coordinates are then used as part of the control for the photogrammetric adjustment.

The GCP helps connect the aerial image model to accurately measured ground coordinates.

Typical equipment used to establish GCP coordinates may include:

• GNSS / RTK Rover

• Total Station

• Other appropriate professional survey methods

What Is a Check Point?

A Check Point is also a surveyed ground point with known coordinates.

The major difference is how it is used.

A Check Point should normally remain independent from the control adjustment when it is being used to assess accuracy.

After processing, the coordinate obtained from the photogrammetric result can be compared against the independently surveyed coordinate.

The difference provides information about how well the mapping result agrees with independent ground observations.

GCP vs Check Point – Simple Comparison

GCPCheck PointFull nameGround Control PointCheck PointCoordinate surveyed?YesYesVisible in drone imagery?YesYesUsed to control adjustment?Normally yesNormally noUsed for independent verification?Not its primary roleYesPhysical target can look identical?YesYesMain purposeCONTROLVERIFY

The difference is primarily the role assigned to the surveyed point—not necessarily the physical target itself.

Why Is This Difference Important?

Imagine you establish ten targets across a construction site.

You accurately survey all ten.

Then you use all ten as GCPs during processing.

The software can report how well the model fits those control points.

But you now have another question:

“How well does the model perform at surveyed locations that were NOT used to control it?”

If you reserved some accurately surveyed targets as Check Points, those independent observations can help answer that question.

This is why professional accuracy assessment should not rely only on the points used to control the model.

A Simple Example

Suppose you deploy:

8 reusable targets

You might assign them according to the project's methodology as:

5 Ground Control Points

3 independent Check Points

The five GCPs are incorporated into the control workflow.

The three Check Points remain independent and are used to assess the resulting output.

This is only an example—not a universal recommendation.

The correct number and distribution should be determined according to project size, geometry, terrain, flight configuration and accuracy requirements.

Can the Same GCP Target Be Used as a Check Point?

YES.

Physically, the same reusable target design can potentially serve either purpose.

For example, MTM Precision supplies:

50 × 50cm GCP Target

100 × 100cm GCP Target

150 × 150cm GCP Target

Any suitable target can potentially be assigned as a GCP or Check Point depending on the project methodology.

What changes is its role in the survey and processing workflow—not necessarily the target itself.

Why Must a Check Point Be Independent?

This is the key concept.

If a point is used to control the adjustment and then treated as an independent accuracy test of that same adjustment, the assessment is no longer truly independent.

A Check Point is valuable because its known coordinate was not used to force the model to fit that point.

You can then compare:

SURVEYED COORDINATE

versus

PHOTOGRAMMETRIC RESULT

to evaluate the difference.

GCP Error vs Check Point Error

These two results should not be interpreted in exactly the same way.

GCP Residuals

These indicate how the adjusted model fits the control observations used during processing.

Check Point Differences / Errors

These indicate how the resulting model performs against independent surveyed points.

A low GCP residual alone does not automatically prove that the entire mapping project has the required independent positional accuracy.

That is one reason Check Points are valuable.

Can I Use All Targets as GCPs?

Technically, a workflow may use many available surveyed points as control.

But for projects requiring independent accuracy evaluation:

Using every surveyed target as a GCP can leave you with no independent Check Points.

Instead of asking only:

“How many GCPs should I use?”

also ask:

“How many independent Check Points should I reserve?”

That is a much stronger survey-planning question.

Do RTK Drones Still Need Check Points?

Check Points can be especially valuable even when using an RTK/PPK drone.

RTK improves the positioning information associated with captured imagery, but professional users may still want independent ground verification.

A possible workflow could involve:

RTK/PPK image positioning

+

Independent surveyed Check Points

Depending on project requirements, GCPs may also be incorporated.

RTK improves positioning capability; Check Points provide an independent way to assess the resulting mapping accuracy.

RTK Drone Without GCP – Can It Work?

Depending on the drone, workflow, correction source, site conditions and required deliverable, some projects may be processed without conventional GCP control.

However:

“No GCP” should not automatically mean “no ground verification.”

Independent Check Points can provide evidence of how the final result compares with accurately surveyed ground positions.

For professional work, that distinction matters.

How Should GCPs Be Distributed?

Good distribution is generally more important than simply concentrating targets in one area.

Depending on the project geometry, control planning may consider:

• Perimeter coverage

• Interior coverage

• Site corners

• Terrain variation

• Elevation changes

• Long corridors

• Irregular boundaries

Do not place all GCPs beside the take-off location simply because it is convenient.

They need to support the geometry of the mapping project.

Where Should Check Points Be Located?

Check Points should also be selected thoughtfully.

The goal is to evaluate the mapping output across meaningful parts of the project area rather than only in one convenient location.

Depending on the project, consider:

• Different areas of the site

• Different elevations

• Interior locations

• Locations away from individual GCPs

• Areas representative of the required deliverable

A Check Point should test the mapping result—not merely confirm performance beside a control point.

GCP Target Size for Control & Check Points

MTM Precision offers three reusable sizes:

50 × 50cm

Compact & Portable

Suitable where the target remains clearly identifiable at the project's planned GSD.

100 × 100cm

General-Purpose Choice

A practical starting option for many drone mapping applications.

It provides a useful balance between field portability and target visibility.

150 × 150cm

Large Visual Target

Useful where the project benefits from a larger target footprint.

Important: GCP Target Size Is About Visibility

Do not confuse physical target size with coordinate accuracy.

A 150×150cm target does NOT automatically provide more accurate coordinates than a 50×50cm target.

Coordinate quality depends primarily on how accurately the reference point is established.

Physical target size mainly affects factors such as:

• Visibility in aerial imagery

• Ease of identification

• Portability

• Deployment requirements

The Target Centre Must Be Clear

Whether the target is being used as a GCP or Check Point:

The exact reference point surveyed on the ground should correspond consistently to the point identified in the aerial image.

A target that is easy to see but difficult to mark precisely can introduce uncertainty.

This is why a clear centre/reference pattern matters.

Example: Construction Drone Survey

Consider a construction site where the team wants to create:

• Orthomosaic

• Site mapping

• Terrain information

• Progress documentation

The field workflow could include:

STEP 1 — Deploy reusable targets

STEP 2 — Survey target coordinates

STEP 3 — Assign selected targets as GCPs

STEP 4 — Reserve selected targets as Check Points

STEP 5 — Conduct UAV flight

STEP 6 — Process imagery

STEP 7 — Evaluate the result against independent Check Points

This creates a much clearer distinction between controlling the model and checking the model.

Example: Quarry Drone Mapping

Quarries can contain:

Large elevation differences

Stockpiles

Excavated areas

Slopes

Changing terrain

For this type of project, thoughtful spatial distribution of both control and independent verification points can be important.

Simply placing many targets near the quarry entrance does not provide representative control across the entire site.

Example: Road & Corridor Mapping

A long road or infrastructure project requires different thinking from a compact rectangular site.

Targets may need to be distributed along the corridor according to the survey methodology.

Independent Check Points can also be positioned to evaluate results across different sections.

Project geometry should influence GCP and Check Point planning.

Common Mistakes

MISTAKE 1 — Calling Every Target a GCP

Not every surveyed target must serve as control.

Some may be Check Points.

MISTAKE 2 — Using Check Points as Control

If the objective is independent verification, do not use those same points to constrain the model.

MISTAKE 3 — Looking Only at GCP Residuals

Good GCP residuals are not the same thing as independent accuracy verification.

MISTAKE 4 — Poor Ground Measurement

A perfectly visible target with an inaccurate surveyed coordinate is still a poor reference.

MISTAKE 5 — Poor Distribution

Targets concentrated in one area may not represent performance throughout the project.

MISTAKE 6 — Assuming RTK Means Verification Is Unnecessary

RTK capability and independent accuracy checking solve different problems.

Frequently Asked Questions

Is a Check Point the same physical product as a GCP target?

It can be.

The physical target may be identical. The difference is how the surveyed point is used during processing.

Should Check Points be surveyed with RTK?

They should be established using an appropriate survey method capable of supporting the required project accuracy, which may include GNSS/RTK or Total Station techniques.

How many Check Points do I need?

There is no universal number.

Project size, geometry, terrain, accuracy requirements and applicable specifications should determine the verification strategy.

Can I turn a GCP into a Check Point during processing?

A surveyed target may be assigned different roles depending on the processing methodology, but a point intended for independent checking should remain independent from the adjustment being evaluated.

Which physical GCP size should I buy?

For general use, 100×100cm is a practical starting option.

50×50cm prioritises portability, while 150×150cm provides a larger visual target.

GCP & Check Point Targets for Drone Survey Malaysia

MTM Precision supplies reusable targets suitable for professional UAV mapping workflows.

Available Sizes

50 × 50cm — Compact

100 × 100cm — General Purpose

150 × 150cm — Large Visual Target

Suitable for:

DRONE SURVEY

UAV MAPPING

PHOTOGRAMMETRY

CONSTRUCTION SURVEY

EARTHWORK

TOPOGRAPHIC MAPPING

QUARRY MAPPING

ROAD & INFRASTRUCTURE

LAND DEVELOPMENT

PLANTATION MAPPING

Contact MTM Precision

MTM Precision Sdn Bhd

Website: www.mtmpre.com.my

Email: mtmpre@yahoo.com

WhatsApp: 016-660 7346

Showroom & Service Centre

No. 29-1 & 29-2, Jalan Bandar 18,

Pusat Bandar Puchong,

47160 Puchong, Selangor, Malaysia.

Supplying Ground Control Point targets and professional surveying accessories throughout Malaysia, including Selangor, Kuala Lumpur, Johor, Penang, Perak, Negeri Sembilan, Melaka, Pahang, Kedah, Perlis, Terengganu, Kelantan, Sarawak and Sabah.