Who can use this feature
Editors of a project within a Professional or Pro + workspace.
If you're capturing data over the same location over time, chances are you are keen to assess the amount of change on the ground. The best way to measure changes between two dates is to use the detect change tool.
Applying the detect change tool
Select your two datasets in the table of contents. These need to have an area of overlap.
Click the
Detect changeicon on the top menu bar.Select the layer/s that you would like to use in the calculation. You can choose from the greenness index, DSM, DTM, or height.
Click run.
A new dataset group will appear in the table of contents and be visible on your map.
You can also access the Detect change tool the following ways:
Right click on one of the selected datasets
Go to Time series
Select Detect change
OR
Open the toolbox on the top menu bar
Go to Time series
Select Detect change
How is the change dataset calculated?
By default, the most recent dataset will be listed as 'dataset 1', and the older dataset will be 'dataset 2'.
The algorithm then simply subtracts the value in every pixel in dataset 2 from the corresponding one in dataset 1.
Example 1
The value of a pixel in my DSM from data captured today is 10m.
The value of a pixel in my DSM from data captured six months ago is 11.
Today's dataset would be considered dataset 1, and the one from six months ago would default as dataset 2.
The 'change' would therefore be 10-11 = -1. As a negative value, this indicates a decrease in elevation. This could be an indication of recent erosion (of course, dataset dependent).
This calculation is applied to every pixel in the image to show the change across the entire scene.
Example 2
The value of a pixel in my greenness index from data captured today is 0.3.
The value of a pixel in my DSM from data captured six months ago is 0.25.
Today's dataset would be considered dataset 1, and the one from six months ago would default as dataset 2.
The 'change' would therefore be 0.3 - 0.25 = +0.05. As a positive value, this indicates an increase greenness. This could be an indication of increased vegetation vitality or biomass (of course, dataset dependent).
Step-by-step
1. Click one dataset (it doesn't matter which order they are in)
2. Hold CTRL (CMD on Mac) and click a second dataset, so both should be highlighted
3. When two datasets are selected, the change detection button will appear on the top menu bar. Click this.
4. Select that layers that you would like to use for the change detection.
It will automatically subtract the older image from the more recent one (you can reverse this up the top of the pop up here too).
5. Click "Run"
Your new layer will appear on the map and your table of contents in a matter of seconds!
Other options
Who can use this feature
Viewers, Commenters and Editors of a project within an Essential, Professional, or Pro + workspace.
Toggle visibility or change layer transparency
As you hover over a layer in the table of contents you will see a slider and an eyeball to the right. Move the slider to change transparency (all the way to the left is completely transparent). Toggle the eyeball open or closed to change its visibility.
These simple tools allow you to quickly view the difference between one layer and the one below it.
Compare layers tool
Select a layer in the table of contents.
Click the
Compareicon on the top menu bar.Swipe from left to right to reveal the differences between the top layer and the one below.
