GenerateContourLines Task

This task generates contour lines from an input raster and converts them to a shapefile.

Example

This simple example plots contour lines at 1300, 1500, and 1700 meters in a digital elevation model (DEM).

; Start the application

e = ENVI()

; Open an input file

File = Filepath('bhdemsub.img', $

  Subdir=['classic','data'], Root_Dir=e.Root_Dir)

Raster = e.OpenRaster(File)

; Get the task from the catalog of ENVITasks

Task = ENVITask('GenerateContourLines')

; Define inputs

Task.INPUT_RASTER = Raster

Task.LEVELS = [1300,1500,1700]

; 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_VECTOR

; Display the result

View = e.GetView()

Layer = View.CreateLayer(Raster)

Layer2 = View.CreateLayer(Task.OUTPUT_VECTOR)

See More Examples.

Syntax

Result = ENVITask('GenerateContourLines')

Input properties (Set, Get): INPUT_RASTER, LEVELS, MINIMUM_LENGTH, OUTPUT_VECTOR_URI

Output properties (Get only): OUTPUT_VECTOR

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:

Properties

This task inherits the following properties from ENVITask:

COMMUTE_ON_DOWNSAMPLE

INPUT_RASTER (required)

Specify a single-band raster from which to generate contour lines; for example, a DEM, gridded bathymetry data, or gridded magnetic anomaly data.

LEVELS (required)

Specify an array of data values to create create contours for. You can provide discrete values; for example, [100, 500, 750] to create contour lines at 100, 500, and 700 meters elevation. Or, use the GenerateIndexArray task to create an array of values as input to the LEVELS property. See the code example in the More Examples section.

MINIMUM_LENGTH (optional)

Specify the minimum contour length to be considered. Lines shorter than this value will be discarded. This property is not set by default, which means that all contours will be included in the output. The units depend on the coordinate system of the input raster.

OUTPUT_VECTOR

This is a reference to the output vector.

OUTPUT_VECTOR_URI (optional)

Specify a string with the fully-qualified path and filename for OUTPUT_VECTOR.

More Examples

This example plots contour lines every 5 meters in a DEM. It uses the RasterStatistics task to get the minimum and maximum elevation values from a DEM. These are passed to the GenerateIndexArray task, which creates the array of values needed for the LEVELS property.

; Start the application

e = ENVI()

; Open an input file

File = Filepath('bhdemsub.img', $

  Subdir=['classic','data'], Root_Dir=e.Root_Dir)

Raster = e.OpenRaster(File)

; Calculate image statistics

StatsTask = ENVITask('RasterStatistics')

StatsTask.INPUT_RASTER = Raster

StatsTask.Execute

minElevation = StatsTask.MIN

maxElevation = StatsTask.MAX

; Create an array of values every 10 meters

IndexTask = ENVITask('GenerateIndexArray')

IndexTask.MIN = minElevation

IndexTask.MAX = maxElevation

IndexTask.INCREMENT = 10

IndexTask.Execute

; Get the task from the catalog of ENVITasks

Task = ENVITask('GenerateContourLines')

; Define inputs

Task.INPUT_RASTER = Raster

Task.LEVELS = IndexTask.OUTPUT_ARRAY

; Define outputs

Task.OUTPUT_VECTOR_URI = e.GetTemporaryFilename('shp')

; 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_VECTOR

; Display the result

View = e.GetView()

Layer = View.CreateLayer(Raster)

Layer2 = View.CreateLayer(Task.OUTPUT_VECTOR)

Version History

ENVI 5.5. 1

Introduced

API Version

4.2