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?


; Start the application
; Create an ENVIRaster
file = FILEPATH('qb_boulder_msi', ROOT_DIR=e.ROOT_DIR, $
  SUBDIRECTORY = ['data'])
raster = e.OpenRaster(file)
metadata = raster.Metadata
; Retrieve the dehydrated hash
dehydratedForm = metadata.Dehydrate()
; Restore the object
newMetadata = ENVIRasterMetadata.Hydrate(dehydratedForm)
Print, newMetadata, /IMPLIED_PRINT


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

Return Value

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



The following standard metadata tags are reserved and will not be present in the hash:

bands, byte order, coordinate system string, data type, file type, geo points, header offset, interleave, lines, map info, pixel size, projection info, rpc info, and samples. Note that the metadata tags are case insensitive but are stored in the returned hash in all uppercase form.

You can build your own hash without instantiating an object to use with the ENVIHydrate function if you follow the template below.




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

Any metadata field not in the reserved list above

Any IDL primitive value: number or string, or arrays of numbers and strings. For the type and cardinality of standard metadata field values, see the ENVI Header Files help topic. Example:

"sensor type" : "QuickBird",



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


API Version


See Also

ENVIRasterMetadata, ENVIRasterMetadata::Dehydrate, ENVIHydratable, ENVIHydrate