ENVIAgCalculateGetisOrdTask

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 is part of ENVI Crop Science, which requires a separate license and installation.

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 ENVIAgCalculateGetisOrdTask.

; 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, REMOVE_FROM_DATA_MANAGER

Output Properties (Get Only): OUTPUT_RASTER

Methods

This task inherits the following methods from ENVITask. See the ENVITask topic in ENVI Help.

AddParameter
Execute
Parameter
ParameterNames
RemoveParameters

Properties

This task inherits the following properties from ENVITask:

COMMUTE_ON_DOWNSAMPLE

COMMUTE_ON_SUBSET

DESCRIPTION

DISPLAY_NAME

NAME

REVISION

See the ENVITask topic in ENVI Help for details.

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 output raster. If you do not specify this property, the output raster is only temporary. Once the raster has no remaining references, ENVI deletes the temporary file.

Version History

1.0	Introduced