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Harris Geospatial / Docs Center / ENVI API / Processing / ClassificationSieving

ClassificationSieving

ENVIClassificationSievingTask

This task removes isolated classified pixels using blob grouping. Low pass or other types of filtering could be used to remove these areas, but the class information would be contaminated by adjacent class codes. The sieve classes method looks at the neighboring four or eight pixels to determine if a pixel is grouped with pixels of the same class. If the number of pixels in a class that are grouped is less than the value that you enter, those pixels will be removed from the class. When pixels are removed from a class using sieving, black pixels (unclassified) will be left. Use ENVIClassificationClumpingTask to remove the black pixels.

Example


The following example performs an unsupervised classification, followed by a sieving, then clumping operation to remove the remaining black pixels.

; Start the application
e = ENVI()
 
; Open an input file
File = Filepath('qb_boulder_msi', Subdir=['data'], $
  Root_Dir=e.Root_Dir)
Raster = e.OpenRaster(File)
 
; Process a spatial subset
Subset = ENVISubsetRaster(Raster, Sub_Rect=[600,200,799,399])
 
; Create a classification ENVIRaster
; Get the task from the catalog of ENVITasks
Task = ENVITask('ISODATAClassification')
 
; Define inputs
Task.INPUT_RASTER = Subset
 
; Define outputs
Task.OUTPUT_RASTER_URI = e.GetTemporaryFilename()
 
; 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
View1 = e.GetView()
Layer1 = View1.CreateLayer(Task.OUTPUT_RASTER)
 
; Get the task from the catalog of ENVITasks
SievingTask=ENVITask('ClassificationSieving')
 
; Define inputs
SievingTask.INPUT_RASTER = Task.OUTPUT_RASTER
 
; Run the sieving task
SievingTask.Execute
 
; Get the clumping task
ClumpingTask = ENVITask('ClassificationClumping')
 
; Define inputs
ClumpingTask.INPUT_RASTER = SievingTask.OUTPUT_RASTER
 
; Define outputs
ClumpingTask.OUTPUT_RASTER_URI = e.GetTemporaryFilename()
 
; Run the task
ClumpingTask.Execute
 
; Add the output to the Data Manager
DataColl.Add, ClumpingTask.OUTPUT_RASTER
 
; Display the result
Layer2 = View1.CreateLayer(ClumpingTask.OUTPUT_RASTER)
 
; Flicker between the original classification and the result
; after clumping
Portal = View1.CreatePortal()
Portal.Animate, 2.0, /FLICKER

Syntax


Result = ENVITask('ClassificationSieving')

Input properties (Set, Get): CLASS_ORDER, IGNORE_VALIDATE, INPUT_RASTER, MINIMUM_SIZE, OUTPUT_RASTER_URI, PIXEL_CONNECTIVITY

Output properties (Get only): DESCRIPTION, NAME, OUTPUT_RASTER

Properties marked as "Set" are those that you can set to specific values. You can also retrieve their current values any time. Properties marked as "Get" are those whose values you can retrieve but not set.

Methods


This task inherits the following methods from ENVITask:

AddParameter

Execute

Parameter

ParameterNames

RemoveParameter

Properties


CLASS_ORDER (optional)

Specify the order of class names in which sieving is applied to the classification image. If you do not specify this property, the classes are processed from first to last.

DESCRIPTION

This property describes the task.

IGNORE_VALIDATE (optional)

This property is now deprecated and has no effect on task behavior. All task property values are validated when they are set, and they throw an error with bad input.

INPUT_RASTER (required)

Specify a raster on which to perform classification clumping.

MINIMUM_SIZE (optional)

Specify the minimum size of a blob (in pixels) to keep. The default value is two pixels.

NAME

This property contains the name of the task.

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.

PIXEL_CONNECTIVITY (optional)

Specify a value of 4 (four-neighbor) or 8 (eight-neighbor) indicating the regions around a pixel that are searched, for continuous blobs. The default is 8.

Version History


ENVI 5.2, Service Pack 1

Introduced

API Version


3.1.0

See Also


ENVITask, ENVITask::Parameter, ENVISubsetRaster, ENVIISODATAClassificationTask, ENVIClassificationSmoothingTask, ENVIClassificationAggregationTask, ENVIClassificationSievingTask



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