Ground control point GCP
Contents |
[edit] Introduction
A ground control point (GCP) is a place or object with a known geographic location (or GPS coordinate) that can be used as a reference point to deliver a precise aerial map for surveying purposes. GCPs are built on the principle of recording the position of an object by calculating the distance and angles between strategically selected points. GPCs can make it possible to map large areas in aerial mapping surveys.
[edit] Parameters for GCPs
GPCs can be photo identifiable objects (such as a manhole cover) or a marked black and white symbol (such as the figure “X” painted on the ground or a small section of a checkerboard). Traditional surveying methods or existing maps can be used to locate the points, but other approaches - such as LiDAR or Google Earth - can also be used.
From an aerial photography perspective, GCPs are a traditional method of defining a location. High contrast colours can be used to make GCPs stand out on drone maps. They should have centrepoints that are clearly defined.
There are other parameters for creating GCPs, including spatial reference systems. These systems are used to relay positions in GCPs by defining several parameters, including:
- Reference ellipsoid. This is the geometric surface that represents the approximate shape of the Earth.
- Reference datum. This is the reference point that is used as the basis for the measurement of all positions.
- Geoid model. This representation of the Earth’s surface uses mean sea level as the reference point of measurement.
- Unit of measurement. This data should be clearly stated - degrees (in latitude and longitude, metres or feet) in relation to how the GCP will be measured in relation to the reference datum.
- Map projection. The method of converting the map from a 3D ellipsoid into a flat plane applies a formula referred to as coordinate transformation.
[edit] Advances in drone surveillance
While GCPs have been a tested method of aerial mapping, there are some inefficiencies associated with the method. There can be logistical challenges when obtaining authorisation for access. In some cases, it may not be possible to gain physical access to the area, even once permission has been granted, due to dangerous terrain or hazardous or remote locations.
In addition, set up can involve a significant amount of time, labour and equipment.
There are several types of equipment that use differential correction technology to provide better data location information; this essentially removes the need for GCP set up. The most commonly used options are real time kinematic (RTK) and post processed kinematic (PPK). RTK makes real time corrections to images captured by GPS while PTK corrects location data after it has been collected and uploaded. In some instances, it can be helpful to use GCPs to enhance information gathered by RTK or PPK enabled technologies, particularly in instances where it is important to capture certain types of precise data regarding accuracy of scale, orientation and so on.
[edit] Related articles on Designing Buildings
- Construction drones.
- Global positioning systems and global navigation satellite systems.
- Ground sample distance GSD.
- Interview with Elly Ball, co-founder Get Kids into Survey.
- Land surveying.
- Laser scanning for building design and construction.
- Post processed kinematic PPK.
- Real time kinematic RTK.
- Universal transverse mercator projection.
- Uses of drones in construction.
Featured articles and news
Quality Planning for Micro and Small to Medium Sized Enterprises
A CIOB Academy Technical Information sheet.
A briefing on fall protection systems for designers
A legal requirement and an ethical must.
CIOB Ireland launches manifesto for 2024 General Election
A vision for a sustainable, high-quality built environment that benefits all members of society.
Local leaders gain new powers to support local high streets
High Street Rental Auctions to be introduced from December.
Infrastructure sector posts second gain for October
With a boost for housebuilder and commercial developer contract awards.
Sustainable construction design teams survey
Shaping the Future of Sustainable Design: Your Voice Matters.
COP29; impacts of construction and updates
Amid criticism, open letters and calls for reform.
The properties of conservation rooflights
Things to consider when choosing the right product.
Adapting to meet changing needs.
London Build: A festival of construction
Co-located with the London Build Fire & Security Expo.
Tasked with locating groups of 10,000 homes with opportunity.
Delivering radical reform in the UK energy market
What are the benefits, barriers and underlying principles.
Information Management Initiative IMI
Building sector-transforming capabilities in emerging technologies.
Recent study of UK households reveals chilling home truths
Poor insulation, EPC knowledge and lack of understanding as to what retrofit might offer.
Embodied Carbon in the Built Environment
Overview, regulations, detail calculations and much more.
Why the construction sector must embrace workplace mental health support
Let’s talk; more importantly now, than ever.
Ensuring the trustworthiness of AI systems
A key growth area, including impacts for construction.