Use the Hydrate static function method to create the object from its dehydrated form. The dehydrated form consists of a hash containing the object’s properties and values. The Hydrate and Dehydrate methods let you store the object state in memory and restore it later.

Representing an object as a hash is necessary for running ENVI analytics with the ENVI Task Engine.

See the ENVIHydrate function if you are creating a general IDL routine that will restore multiple object types.

For additional information, see What are Hydrate and Dehydrate routines used for?

Example

; Start the application
e = ENVI(/HEADLESS)
 
; Select input files.
ULFile = 'qb_boulder_msi_UpperLeft.dat'
ULRaster = e.OpenRaster(ULFile)
 
URFile = 'qb_boulder_msi_UpperRight.dat'
URRaster = e.OpenRaster(URFile)
 
LLFile = 'qb_boulder_msi_LowerLeft.dat'
LLRaster = e.OpenRaster(LLFile)
 
LRFile = 'qb_boulder_msi_LowerRight.dat'
LRRaster = e.OpenRaster(LRFile)
 
SourceRasters = [[ULRaster, URRaster], [LLRaster, LRRaster]]
 
; Create a metaspatial raster
MSRaster = ENVIMetaspatialRaster(SourceRasters)
 
; Retrieve the dehydrated hash
dehydratedForm = MSRaster.Dehydrate()
MSRaster.close
 
; Restore the object
newImage = ENVIMetaspatialRaster.Hydrate(dehydratedForm)
Print, newImage, /IMPLIED_PRINT

Syntax

Result = ENVIMetaspatialRaster.Hydrate(DehydratedForm, ERROR=value)

Return Value

The result is a reference to a new object instance of this virtual raster class.

Arguments

DehydratedForm

Key

Description

factory

Required. A string value of MetaspatialRaster indicating what object type the hash represents.

input_rasters

Required. A 2D array of input ENVIRasters. The following rules apply:

  • Source rasters must have the same number of bands and the same spatial dimensions.
  • One exception is that the outside edges can be shorter than the rest as long as all rasters in the entire row or column are equal in size.
  • Specify empty tiles with null objects by entering 'NullObject' instead of using ENIVRasters.
  • Padded and empty tiles will have a PIXEL_STATE set to 2 (NoData). The pixel data will be invalid in these areas. To export the raster to disk, provide a data ignore value.
  • Metadata values are passed from the source rasters to the virtual raster only if the values are the same in all source rasters.
  • Input rasters do not need to be georeferenced. If the top-left tile contains a spatial reference, that reference will be used for the virtual raster. You can override the spatial reference by using the spatialref key.
  • The order of the array elements determines the layout of the tiles in the metaspatial raster.

The following examples use data files that are available from our ENVI Tutorials web page. Click the API Gridding Examples link to download the .zip file to your machine, then unzip the files. Update the file location with your own directory.

Example 1:

"input_rasters": [
   [
      {
         "url": 
"/usr/local/INSTALL_DIR/envi/mydata/tutorial_data/apigriddingexamples/qb_boulder_msi_UpperLeft.dat",
         "factory": "URLRaster"
      },
      {
         "url": 
"/usr/local/INSTALL_DIR/envi/mydata/tutorial_data/apigriddingexamples/qb_boulder_msi_UpperRight.dat",
         "factory": "URLRaster"
      }
   ],
   [
      {
         "url": 
"/usr/local/INSTALL_DIR/envi/mydata/tutorial_data/apigriddingexamples/qb_boulder_msi_LowerLeft.dat",
         "factory": "URLRaster"
      },
      {
         "url": 
"/usr/local/INSTALL_DIR/envi/mydata/tutorial_data/apigriddingexamples/qb_boulder_msi_LowerRight.dat",
         "factory": "URLRaster"
      }
   ]
]

Example 2:

"input_rasters": [
   [
      {
         "factory": "URLRaster",
         "url": 
"/usr/local/INSTALL_DIR/envi/mydata/tutorial_data/apigriddingexamples/qb_boulder_msi_UpperLeft.dat"
      },
      {
         "factory": "NullObject"
      }
   ],
   [
      {
         "factory": "NullObject"
      },
      {
         "factory": "URLRaster",
         "url": 
"/usr/local/INSTALL_DIR/envi/mydata/tutorial_data/apigriddingexamples/qb_boulder_msi_LowerRight.dat"
      }
   ]
]

name

A string that identifies the raster.

spatialref

An ENVIStandardRasterSpatialRef, ENVIPseudoRasterSpatialRef, or ENVIRPCRasterSpatialref hash if you want to reproject the source rasters to a common spatial reference. Example:

spatialRef: {
   "factory": "StandardRasterSpatialRef",
   "rotation": 0.00000000,
   "tie_point_pixel": [0.00000000, 0.00000000],
   "coord_sys_code": 32611,
   "pixel_size": [30.000000, 30.000000],
   "tie_point_map": [493785.00, 4899315.0]
}

Keywords

ERROR (optional)

Set this keyword to a named variable that will contain any error message issued during execution of this routine. If no error occurs, the ERROR variable will be set to a null string (''). If an error occurs and the routine is a function, then the function result will be undefined.

When this keyword is not set and an error occurs, ENVI returns to the caller and execution halts. In this case, the error message is contained within !ERROR_STATE and can be caught using IDL's CATCH routine. See IDL Help for more information on !ERROR_STATE and CATCH.

See Manage Errors for more information on error handling in ENVI programming.

Version History

ENVI 5.4

Introduced

API Version

4.2

See Also

ENVIMetaspatialRaster, ENVIMetaspatialRaster::Dehydrate, ENVIHydratable, ENVIHydrate