Georeferencing is the method of assigning real-world coordinates to each pixel of the raster. Usually, these coordinates are obtained by doing proper field surveys and collecting coordinates with a GPS device for a few easily identifiable features in the image or the map.
The importance of Georeferencing lies in its ability to turn non-spatial imagery into spatial raster data for use in a variety of Stages in GIS.
Some Relevance of Georeferencing includes:-
- Pointing and clicking on the map to determine and extract the coordinates of a point.
- Aid to calculate distances and areas, and to determine other information.
Major Importance of Georeferencing are listed below;
1️⃣ Data Comparison: Georeferencing is especially useful for comparisons against other geographic data and historical data.
2️⃣ Merging and Assembly of Data:
It is easier to combine different forms of data together if they have been georeferenced for example, satellite or aerial imagery with Scanned Maps or Soft copy Maps
3️⃣ Increased Confidence of Data:* Georeferencing also improves the consistency, completeness and reliability of spatial data, providing a greater layer of confidence to decision-making.
Methods of Georeferencing:
A. Image to Point Registration:
This is a process used in geographic information systems (GIS) to assign spatial coordinates (latitude and longitude) to specific points or features within an image.
It is the General form of Georeferencing known to many, which is important for integrating and overlaying image data with other geospatial datasets in order to create accurate and meaningful maps or analyses.
The Georeferencing process involves matching points on the image with their corresponding locations in the real world.
Typically, a set of control points are identified on the image, and their corresponding geographic coordinates are known. The software then uses these control points to establish a transformation function that can accurately relate the image coordinates to it’s original geographic coordinates.
For example, if you have an aerial photograph or a satellite image that lacks spatial reference information, you can use image to point Georeferencing to align it with a map or other Georeferenced data.
Image to point Georeferencing is a crucial step in the integration of remote sensing data, such as satellite imagery or aerial photographs, into GIS workflows. It allows for the creation of accurate and spatially referenced maps that can be used for various applications, including environmental monitoring, land use planning, and natural resource management.
B. Image to Image Registration:
It involves aligning or registering two or more images to each other in a geospatial context. This process is commonly used in geographic information systems (GIS) and remote sensing applications where multiple images need to be compared, overlaid, or integrated for analysis or mapping purposes.
The goal is to ensure that the features in different images align accurately in geographic space.
The typical scenario for image-to-image Georeferencing involves having one reference image with known geospatial information (such as a Georeferenced map, satellite image, or aerial photograph) and one or more target images that need to be aligned with the reference.
The process involves identifying corresponding points in both the reference and target images, specifying their geographic coordinates, and then using these control points to perform a geometric transformation.This is commonly done by identifying easily recognizable features, such as road intersections or prominent landmarks, in both the image and a reference map. By specifying the known geographic coordinates of these points, the software can calculate the transformation needed to Georeferenced the entire image.
Common techniques for image-to-image Geo-referencing include polynomial transformations, affine transformations, or projective transformations, depending on the level of distortion present in the imageries. Control points can be selected manually or automatically, and the transformation is applied to ensure accurate alignment.
Applications of image-to-image Geo-referencing includes:
1️⃣ Change Detection: Comparing images of the same area taken at different times to identify changes, such as land use changes, urban expansion, or environmental impacts.
2️⃣ Image Fusion: Integrating data from different sensors or platforms, such as merging a high-resolution optical image with a lower-resolution thermal image.
3️⃣ Map Composition: Combining various images for map creation or updating, especially when dealing with diverse data sources like satellite imagery, aerial photography, or drone imagery.
4️⃣ Feature Extraction: Aligning images to accurately extract features or objects, such as roads, buildings, or vegetation etc.
5️⃣ Terrain Analysis: Aligning images for terrain modeling and analysis, particularly when dealing with elevation data.
Image-to-image georeferencing plays a crucial role in ensuring that multiple datasets are spatially coherent, allowing for accurate analysis and decision-making in GIS and remote sensing applications.
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Signed ✍ :
a. Surv. Uju O. IZUEGBU, MNIS
Chair: YSN-FCT*
*b. Angela Omamuyovwi ANYAKORA*
*Head: Education Committee YSN-FCT*
*c. Victor Nwaogu*
*Education Committee YSN-FCT*
