I want to obtain the size of unchanged, decreased, and increased area etc (just like shown in image below) from 2 classification images in 2000 and 2007.
How do I do this in ERDAS?
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[GIS] Doing change detection in ERDAS
change detectionerdas-imagine
Related Solutions
To answer your question yes, this is possible but it is important to consider a few other things to make sure you are getting proper results.
In theory this is a simple subtraction problem, however there are a few things that need to be accounted for in order to obtain the correct results. First and foremost the two rasters need to be orthogonal and concurrent. Meaning that they have the same extent and that the there cell centers line up. This will guarantee that you are subtracting the same cell from the different time steps.
Additionally it is important that you subtract the old raster from the new raster to simplify the interpretation of the results. This will ensure that negative cells coincides with what would be considered erosion and positive cells coincide with what would be considered deposition.
Another complicating detail to consider but this seems a bit overkill at least for your question (and what sort of magnitude of change you are trying to see) is uncertainty in the rasters that you are using in your calculation. There are many methods out there to quantify uncertainty in a raster.
If looking at volumetric change is something that you do a lot of, I would encourage you to look into the Geomorphic Change Detection (GCD) Software. Depending on what version of Arc you use it has a plug-in version and an Add-In version. GCD puts tools to guarantee orthogonality/concurrency, tools to calculate uncertainty and many other tools that make calucating change between rasters in one place for you, is very well documented, and provides different methods to report your results. Plus it is open source and free!
You can use the Signature Editor in ERDAS to use Shapefiles to create signature files. The Signature Editor is found under the supervised classification in the raster ribbon of ERDAS.
You must have whatever image you want to classify open in Imagine.
Your shapfile must have a text attribute. This field would have the name of each class associated with each polygon that will become an area of interest.
From the Signature Editor select edit>read shape. Nagivate to the shapefile and make sure to then select the attribute text field with the class name associated with feature.
This next part can be confusing, now click on the image that you want to classify in Imagine. This will essentially create a new AOI while populating the signature editor with the features from your shapefile.
You can now merge, delete, add, etc and save to a .sig file.
Best Answer
You can do it by this way: 1. Go to 'Image Interpreter >>> Utilities >>> Change detection'. 2. Give before and after images. 3. It will produce the 'Difference' image as well as 'thematic image' of five classes namely decreased, some decreased, unchanged, some increase and increased.
From which you can calculate the size of your decreased, increased and unchanged.