Change detection in GIS is a method of understanding how a given area has changed between two or more time periods. Change detection is helpful for understanding the change in forest coverage, ice sheets, and land use. Change detection involves comparing changes between aerial photographs taken over different time periods that cover the exact same geographic area.
Change detection can be used to measure four different types of change:
- Change in the identify of a feature over time. For example, the change in type of retail store at a given location. A local restaurant may go out of business and be replaced by a toy store. The actual physical building hasn’t changed, the type of categorized land use hasn’t change (commercial), but the specific identity of the store has change.
- Change of a feature’s location over time. Change detection can be used to track the movement of a feature.
- Change of a feature’s shape over time. Change detection can be used to understand shrinkage in a specific specie’s habitat over time or the changes in the shape of a river or lake.
- Change in a feature’s size over time. Change detection can also measure the extent of a feature. Does the urban area grow or shrink between two time points?
Articles about Change Detection in GIS
Change Detection Using ArcGIS
In ArcGIS, change detection can be calculate between two raster datasets by using the raster calculator tool.
Change Detector script from Bruce Harold – From the ArcScript site, this tool that “computes the added, deleted and unchanged features between original and revised editions (or versions) of a data set by considering any combination of geometry and attributes.”
To compare the differences between two vector datasets use the Feature Compare tool under Data Management –> Data Comparison.
Change Detection Using QGIS
Change detection in QGIS can be accomplished through the plugin DTClassifier.
To create a third GIS dataset showing the difference between two datasets go to Vector –>GeoProcessing and then select the Difference function.
Change Detection in ENVI
This video looks at using ENVI to model multi-temporal changes using orthophotography.
Change Detection in ERDAS
This video looks at change detection to understand changes in a building layer by comparing roof tops between two different files using ERDAS.
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