AgCalculateGetisOrd Task
This task creates a Z-score raster to find regions that are statistically significant.
ENVI calculates Getis-Ord Gi* local statistics (Getis and Ord, 1992) to group neighboring pixels of similar value into clusters. The algorithm evaluates each pixel and its surrounding pixels within a specified distance to classify the pixel as "hot" or "cold" (statistically significant clusters of high or low values, respectively) or neutral (not statistically significant). Hotspot analysis can be used to look for variations in crop health.
This task requires a separate license for the ENVI Crop Science Module; contact your sales representative for more information.
Example
This example creates a Z-score raster from a spectral index image of alfalfa fields.
The source image consists of layer-stacked Sentinel-2A visible, near-infrared, and shortwave-infrared bands with a spatial resolution of 10 meters. The image is from eastern Idaho, USA. The accompanying region of interest (ROI) file encompasses alfalfa fields. It is used to mask out all non-alfalfa pixels from the source image. The masked raster is then used to create a Modified Simple Ratio index, which is used as input to AgCalculateGetisOrd Task.
; Start the application
e = ENVI()
; Open an input file
File = Filepath('CircularFields_Sentinel2A.dat', $
Subdir=['data', 'crop_science'], $
Root_Dir=e.Root_Dir)
Raster = e.OpenRaster(File)
; Only process the actively growing fields
; using an ROI mask
ROIFile = Filepath('CircularFields_AlfalfaROI.xml', $
Subdir=['data', 'crop_science'], $
Root_Dir=e.Root_Dir)
ROI = e.OpenROI(ROIFile)
maskedRaster = ENVIROIMaskRaster(Raster, ROI)
; Create a Modified Simple Ratio index
MSRImage = ENVISpectralIndexRaster(maskedRaster, 'MSR')
; Get the task from the catalog of ENVITasks
Task = ENVITask('AgCalculateGetisOrd')
; Define the task inputs
Task.INPUT_RASTER = MSRImage
Task.DISTANCE = 10 ; meters
; Run the task
Task.Execute
; Get the collection of data objects currently
; available in the Data Manager
DataColl = e.Data
; Add the output to the Data Manager
DataColl.Add, Task.OUTPUT_RASTER
; Display the result
View = e.GetView()
Layer = View.CreateLayer(Task.OUTPUT_RASTER)
Layer.QUICK_STRETCH = 'Equalization'
Syntax
Result = ENVITask('AgCalculateGetisOrd')
Input Properties (Get, Set): DISTANCE, INPUT_RASTER, OUTPUT_RASTER_URI
Output Properties (Get Only): OUTPUT_RASTER
Methods
This task inherits the following methods from ENVITask:
Properties
This task inherits the following properties from ENVITask:
This task also contains the following properties:
DISTANCE (required)
Specify the radius of the area around each pixel used to calculate the local mean. If the input raster has a valid spatial reference, then the radius is measured in meters. Otherwise, it is measured in pixels.
INPUT_RASTER (required)
Specify a single-band input raster.
OUTPUT_RASTER
This is a reference to the output raster of filetype ENVI.
OUTPUT_RASTER_URI (optional)
Specify a string with the fully qualified filename and path of the associated OUTPUT_RASTER. If you do not specify this property, or set it to an exclamation symbol (!), a temporary file will be created.
Version History
|
Crop Science 1.0 |
Introduced |