Drone Surveying Basics About Ground Control

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Posted on
June 3, 2024
Drone Surveying & Ground Control
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With the rising role of drone surveying in multiple industries, fast and accurate collection of data for mapping and monitoring has become an important part of many businesses. Such services feature some characteristic peculiarities, and one of them is ground control points, or GCPs, which constitute a necessary element determining the results’ accuracy and consistency. GCPs are certain objects or markers that could be placed at a given location prior to a drone’s data collection. These points are used for exact georeferencing, making it possible for the drone to save exact real-world coordinates for every image it generates and align particular markers with images to be taken. 

In today’s article, we will disclose the basic information about GCPs, describe how they should be installed or used, review some other georeferencing methods, and give recommendations as to how the data collected with GCPs should best be captured and submitted. Such a review is important because drones are increasingly being used for surveying and other data collection operations across a variety of industries, and therefore, some basic information should be at the operators’ disposal.

How do I measure my ground control?

Precise measurement of ground control points (GCPs) is essential for obtaining dependable surveying data. There are several methods used to measure GCP with precision:

  • GPS Receivers: Use high-precision GPS receivers to get accurate coordinates for GCPs. GPS technology provides reliable geospatial positioning data.
  • Surveying Equipment: Total Stations and Global Navigation Satellite Systems (GNSS) receivers offer more accurate measurements, especially in difficult terrains or environments where GPS signals may be obstructed.
  • Considerations: The method of measurement chosen should depend on project requirements such as accuracy, terrain complexity, or budgetary constraints.

What should my markers look like?

Effective GCP markers have some specific characteristics that make them visible, durable, and compatible with drone operations:

  • Visibility: Go in for colored markers that can easily be seen in aerial images, such as those having distinct colors that are bright enough due to their adequacy of size or high contrast. Bright colors like orange or yellow are often recommended.
  • Durability: To survive weather conditions, including rainfall, wind storms, or exposure to sunlight, paint your marks with weatherproof materials.
  • Non-Interference: Nothing should stand between your GCPs; otherwise, you’ll have trouble with drones flying over them, preventing any reflection that might come from structures taller than these points. noninterference by means of not marking any obstacles towards visibility in the survey area’s direction Avoid tall structures or reflective surfaces near GCPs.

The commonly used GCP markers include ground targets, flags, and painted markers, as each of them has its own advantages in various surveying scenarios.

Where should I place my markers?

Proper placement of GCPs is important for accurate and reliable surveying outcomes.

  • Even Distribution: Distribute GCPs evenly across the survey area to avoid having gaps in one region that may result in measurement errors.
  • Accessibility: Considering things like terrain accessibility and safety, ensure that the placement and retrieval of ground control points by field crews are facilitated.
  • Obstruction Avoidance: Place markers away from obstructions, shadows, or vegetation that could obscure visibility or affect measurement accuracy.

The optimal location of GCPs helps to minimize errors and improve the overall quality of drone-based survey data.

What if I don’t have marker mats or can’t mark the site with paint?

In situations where conventional GCP markers are impractical or unavailable, alternatives exist for establishing reference points:

  • Virtual Markers: Software-based GCPs can be made out of imagery or digital mapping data. Virtual markers are flexible because they do not need physical installation for adjustment purposes.
  • Natural Features: Identify permanent landmarks or geological features within the survey area that can serve as reference points. Natural features provide stable reference points over time.
  • Temporary Markers: Use reusable objects, such as temporary signs or paint markings for such a moment. Temporary markers offer a cost-effective solution for short-term projects.

Alternatively, these methods provide flexibility but may require additional validation and calibration to ensure accuracy comparable with traditional markers.

Best practices for capturing your markers

Attaining accurate GCP data involves observing best practices throughout the entire survey process.

  • Flight Planning: Plan drone flights to optimize GCP visibility and coverage, taking into account factors including flight altitude, overlap, camera settings, etc.
  • Camera Settings: Set up the camera for the best optical resolution, exposure, and image overlap to ensure accurate GCPs in the course of aerial surveys.
  • Post-Flight Processing: Utilize customized software to evaluate GCP positions and verify them against ground control points.

Following these practices improves the precision of GCP data collected during drone surveys.

What do I need to do so that my survey is processed with GCPs?

Include the following details when attaching GCP data to a survey for processing:

  • Georeferencing Information: Provide exact coordinates (latitude, longitude, and altitude) as well as the used projection system for GCPs.
  • GCP Identification: Indicate clear labels for easy identification and referencing during processing, such as unique identifiers or names.
  • Quality Assurance: Check for accuracy errors through error correction tests on submitted GCP data, including validation reports and ground truth comparisons.

Properly documented and validated GCP data accelerates processing flow, thereby improving the final survey results’ accuracy.

Conclusion

Building strong knowledge bases regarding ground control in relation to drone surveying helps achieve reliable mapping outcomes. The success of any given drone surveying project relies on every detail mentioned about measuring and marking out, strategic placement, various method alternatives, capturing best practices, and submission prerequisites. By adopting best practices, using the right tools and techniques, and being precise in terms of both accuracy and quality, surveyors will be able to optimize their workflows to increase data accuracy, thus producing meaningful analytics useful across industries.

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