CompassData, Inc. FAQs About Ground Control Points Archive
Welcome to our Ground Control Points (GCP) Archive FAQ page. Here, you'll find answers to the most common questions about using, accessing, and understanding Ground COntrol Points (GCPs) for geospatial projects. Ground Control Points are essential for ensuring the accuracy of satellite imagery, aerial photography, and LiDAR data by providing precise georeferencing.
Whether you're a GIS professional, surveyor, or remote sensing analyst, these FAQs are designed to help you make the most of high-quality GCP data and understand how it supports reliable, accurate mapping and analysis.
What are Ground Control Points in remote sensing and mapping?
Ground Control Points (GCPs) are precisely surveyed locations on the Earth’s surface with known geographic coordinates, used to georeference satellite imagery, aerial photos, LiDAR, and drone data. In remote sensing and mapping, GCPs serve as reference points to correct positional inaccuracies and tie digital data to real-world coordinates—essential for creating accurate maps and geospatial products.
Why are Ground Control Points important in aerial and satellite imagery?
Ground Control Points are vital for ensuring geospatial accuracy in aerial and satellite imagery. They provide fixed reference locations that align image pixels to precise geographic coordinates. This process, called orthorectification, removes distortions caused by camera angles, elevation changes, and sensor geometry—enabling consistent, measurable, and reliable imagery for GIS, surveying, and spatial analysis applications.
How do Ground Control Points improve mapping accuracy?
Ground Control Points (GCPs) significantly enhance mapping accuracy by serving as ground-truth references during image processing. When incorporated into photogrammetric workflows, GCPs correct distortions, improve spatial alignment, and reduce horizontal and vertical errors. This results in more accurate digital elevation models (DEMs), orthomosaics, and GIS datasets—especially important for high-resolution or engineering-grade projects.
What is the difference between Ground Control Points and Check Points?
While both Ground Control Points and Check Points are surveyed locations with known coordinates, they serve different purposes. Ground Control Points (GCPs) are used during image processing to calibrate and align data. Check Points, on the other hand, are reserved for post-processing accuracy validation—helping verify the spatial integrity of georeferenced imagery without influencing the processing itself. Together, they ensure high confidence in final geospatial products.
How are Ground Control Points collected?
Ground Control Points (GCPs) are typically collected using high-precision GPS, GNSS receivers, or total stations operated by trained surveyors. Field collection follows strict geodetic and quality assurance protocols, often in accordance with ISO 9001:2015-certified standards. Each GCP includes documentation such as site sketches, field photos, and metadata, ensuring transparency, repeatability, and accuracy in geospatial workflows.
What level of accuracy can be achieved with Ground Control Points?
The achievable accuracy of Ground Control Points (GCPs) depends on the survey method and quality classification. High-quality Ground Control Points (GCPs) can achieve centimeter-level precision, typically ranging from 1–5 cm for Quality-0 control points. Lower quality levels may provide accuracies within sub-meter to multi-meter ranges. Choosing the appropriate accuracy level is critical for applications such as infrastructure development, flood modeling, and precision agriculture..
Can Ground Control Points be used for drone mapping?
Absolutely. Ground Control Points (GCPs) are essential for enhancing the geospatial accuracy of drone mapping projects. By anchoring aerial imagery to known ground coordinates, Ground Control Points (GCPs) improve orthomosaic alignment, reduce geolocation drift, and boost overall positional accuracy—especially when GPS RTK/PPK is unavailable or insufficient. GCPs are a best practice for drone-based surveying, construction site monitoring, and asset inspection.
What file formats are Ground Control Points typically delivered in?
Ground Control Points (GCPs) are commonly delivered in a variety of industry-standard file formats, including ESRI shapefiles (SHP), Google Earth KML/KMZ, and CSV or TXT spreadsheet formats. These files include coordinate data (Latitude, Longitude, Elevation, Easting, Northing), metadata, and projection information—making them easy to import into GIS, CAD, remote sensing, and photogrammetry software environments.
Are Ground Control Points necessary for LiDAR data processing?
Yes, Ground Control Points are frequently used for LiDAR QA/QC and calibration, particularly in Non-Vegetated Vertical Accuracy (NVA) assessments. While LiDAR sensors can produce highly accurate elevation models, GCPs validate the vertical and horizontal accuracy of point clouds and digital terrain models. Using GCPs in LiDAR workflows enhances data confidence for applications such as flood modeling, terrain analysis, and infrastructure mapping.
What industries rely on Ground Control Points for accurate geospatial data?
Ground Control Points are a critical asset in multiple industries that require precise, georeferenced spatial data. These include land surveying, civil engineering, construction, urban planning, forestry, agriculture, defense, mining, and environmental monitoring. GCPs ensure that remote sensing and mapping outputs meet regulatory standards, engineering specifications, and operational accuracy needs across a wide range of geospatial applications.
CompassData Ground Control Points Archive – FAQs
What makes CompassData’s Ground Control Points different from other GCP providers?
CompassData offers one of the world’s largest commercial Ground Control Point (GCP) archives, with over 70,000 high-quality, pre-surveyed locations across all seven continents. Each Ground Control Point (GCP) is collected under ISO 9001:2015-certified procedures, with full documentation including coordinate files, site photos, and accuracy reports—ensuring unmatched reliability and global consistency for mapping, photogrammetry, and LiDAR applications.
What is included in a CompassData Ground Control Point delivery package?
Each CompassData Ground Control Point includes a complete set of deliverables: coordinate files in Latitude, Longitude, Elevation, and projected formats; metadata; an accuracy report; a site sketch drawn by the surveyor; four directional photos and a close-up image of the site; and optional geofiles in ESRI shapefile and Google Earth KML formats. These deliverables ensure full transparency and easy integration into GIS and remote sensing workflows.
How accurate are CompassData Ground Control Points?
CompassData classifies GCPs into five quality tiers based on 95% Circular and Linear Error metrics (CE/LE). Quality-0 GCPs offer exceptional horizontal and vertical accuracy of 1–5 cm, ideal for high-precision applications. Lower tiers—Quality-1 through Quality-4—offer scalable accuracy levels, enabling users to choose the most cost-effective control based on project requirements.
Does CompassData support Ground Control Points for LiDAR QA/QC?
Yes, CompassData provides Ground Control Points specifically for LiDAR Non-Vegetated Vertical Accuracy (NVA) validation and Quality Assurance/Quality Control (QA/QC). These pre-surveyed photo-identifiable GCPs eliminate the need for costly and time-consuming field visits—accelerating workflows and maintaining accuracy standards for LiDAR calibration, especially in hard-to-access regions.
Can I get airport-specific Ground Control Points from CompassData?
Absolutely. CompassData’s archive includes airport Ground Control Point clusters at over 1,100 international and regional airports. These GCPs are processed in accordance with FAA DO-200A guidelines, making them ideal for both authoritative and commercial image production around aerodromes—especially where regulatory compliance and precision are critical.
Does CompassData offer Ground Control Points GCPs that don’t require a field visit?
Yes. CompassData offers Photo-ID Ground Control Points and Remotely Sensed Ground Control Points® (RSGCP®) that are ideal for supporting imagery production and QA/QC without requiring a field team. RSGCPs are derived from Synthetic Aperture Radar (SAR) or high-resolution satellite imagery, offering precision of ≤1m (RS-1) or ≤3m (RS-2) for use in politically or logistically restricted areas.
How can I view the CompassData Ground Control Points archive?
The CompassData Ground Control Points archive is visualized on an interactive global map, allowing users to zoom in on specific locations and view associated site photos, accuracy reports, and station diagrams. A truncated version of the archive is also available for download as a KML or shapefile, making it easy to explore existing coverage and request data in your area of interest.
Does CompassData support custom GCP acquisition projects?
Yes. In addition to its extensive off-the-shelf archive, CompassData provides custom Ground Control Point acquisition services tailored to client specifications. Whether you need Quality-0 Ground Control Points (GCPs) for a remote infrastructure project or specialized control points for UAV, satellite, or SAR missions, CompassData’s global team of professional surveyors can deploy quickly and deliver certified results.
What coordinate systems and datums does CompassData support?
CompassData supports all major geodetic datums and projected coordinate systems. Ground Control Points (GCPs) can be delivered in WGS84, NAD83, ETRS89, and other local systems, with transformations performed using industry-standard geospatial tools. This flexibility ensures seamless integration into various GIS, remote sensing, CAD, and mapping software platforms.
How do I request a sample of CompassData Ground Control Points?
To request sample Ground Control Point data from CompassData, simply contact the team through the “Contact Us” form on the Ground Control Points Archive page. You’ll receive access to a sample dataset showcasing available metadata, coordinate formats, accuracy reports, and visual documentation.