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General Terms
Georeference
The process of assigning real coordinates to a digital image or dataset, tying it to the Earth's surface.
Georeferencing is the process of assigning geographic location to a digital image, map, or other spatial dataset by connecting it to a specific coordinate system. This allows data to be used in geospatial analyses and combined with other geodata.
Types of georeferencing:
- Direct georeferencing - coordinates determined at measurement time (GNSS, total station)
- Indirect georeferencing - connection using control points (GCP)
- Relative georeferencing - connection to other georeferenced data
Georeferencing process:
- Determining control points (GCP) in the field with GNSS
- Identifying control points in image or data
- Calculating mathematical transformation
- Applying transformation to all data
- Precision assessment and control
Transformation types:
- Affine transformation - scale, rotation, shift correction
- Polynomial transformation - for more complex distortions
- Rational polynomial function - for satellite images
- Helmert transformation - between coordinate systems
Applications in surveying:
- Drone imagery - orthophoto creation
- LiDAR data - point cloud connection
- Historical map digitization
- Scanned plan connection
- Satellite image processing
Georeferencing precision:
Precision is affected by:
- Number and distribution of control points
- Control point measurement precision
- Source data quality
- Selected transformation method
GCP requirements:
- At least 4-6 points for larger objects
- Uniform distribution across territory
- High coordinate precision (RTK or static GNSS)
- Clearly identifiable in images
Proper georeferencing is critical to ensure data compatibility with other geospatial data and its use in design and construction.