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Purpose

 

The Digital Elevation Model tiles, which are needed to cover the specified area, are downloaded from the internet, mosaiced and eventually interpolated.

 

Technical Note

 

The area of interest, which has to be covered by the extracted Digital Elevation Model, can be specified by entering either the area cartographic co-ordinates or a reference image or a list of images.

 

Once the Digital Elevation Model tiles have been downloaded, they are stored in a folder called  GTOPO30_DIR in the default work directory. In case the relevant Digital Elevation Model tiles had been previously downloaded and stored in the PC, they are automatically retrieved and used. Note that the specific environment variable (i.e. GTOPO30_DIR) can be set in order to store the Digital Elevation Model tiles in different user defined folders.

 

In case one of the Digital Elevation Model tiles is not found in the internet, or the internet connection fails before or during the data downloading, a message is written in the Process.log file.

 

Note: Since August 2015, the GTOPO30 tiles have to be manually downloaded from the USGS Earth Explorer (which requires registration), data are located under the Digital Elevation category. The downloaded tile have to be copied in the GTOPO30_DIR folder located in the working directory or in any other directory if specified in the Directories Preferences.

In the Log file you will find the name of the tile(s) needed if not already present in the GTOPO30_DIR. Alternately, it is possible to download all the tiles once and then save them on a local/network drive so that no internet access is needed to extract a GTOPO30 dem again.

 

Note: Subtract Geoid (Other Parameters)

By setting this flag the output product will be referred to the ellipsoid. The EGM96 geoid is subtracted. Set this flag if the extracted Digital Elevation Model has to be used for further processing in SARscape.

 

 

 

Input Files

 

OPTIONAL Reference Slant Range Image

Input file(s) name of the image to be used as geographic reference for the Digital Elevation Model extraction. This file is mandatory if the cartographic co-ordinates are not specified. In case a geocoded image is used, the "Cartographic System" specified below must be the same of the reference image. The geographical extent of the output Digital Elevation Model corresponds to the total coverage of the Reference file list.

 

DEM/Cartographic System

 

Output Projection

The parameters relevant to the Cartographic System of the output Digital Elevation Model must be entered:

 

State

Definition of the country or general projection systems.

 

Hemisphere

Definition of the hemisphere. This is chosen according to the selected State and Projection.

 

Projection

Definition of the projection system of the selected State. In case that a general projection system is selected in State, the Projection is automatically set.

 

Zone

Definition of the zone. This is chosen according to the selected State and Projection.

 

Ellipsoid

Definition of the ellipsoid. This is chosen according to the selected State and Projection.

 

Datum Shift Parameters

Definition of the datum shift parameters. These are chosen according to the selected State and Projection.

 

Reference Height

A reference ellipsoidal height can be provided. Default Reference Height is 0.

 

Cartographic Parameters

The reference parameters for some projection systems (e.g. Stereographic, Polar Stereographic, Gnomonic, Mercator, Miller, Albers, etc.) can be set.

 

Parameters - Principal Parameters

 

Slope

By setting this flag, three slope files are created: slope east-west, slope north-south in degree between -90 and 90. The third out is the absolute slope (sqrt(ew^2 +ns^2)) in degree, between 0 and 90 degree.

 

By setting the following parameters it is possible to specify a spatial region for the Digital Elevation Model extraction (co-ordinates are referred to the output cartographic reference system).

 

The Westernmost cartographic co-ordinate.

 

The Easternmost cartographic co-ordinate.

 

The Northernmost cartographic co-ordinate.

 

The Southernmost cartographic co-ordinate.

 

X Grid Size

The grid size in X direction of the output data must be defined; the default unit of measure is meters.

Note that - for the Geographic projection - if values higher than 0.2 are entered they will be considered as metric units and then automatically, and roughly, converted from meters to degrees; if values lower than 0.2 are entered they will be considered as degree and used as such without any conversion.

 

Y Grid Size

The grid size in Y direction of the output data must be defined; the default unit of measure is meters.

Note that - for the Geographic projection - if values higher than 0.2 are entered they will be considered as metric units and then automatically, and roughly, converted from meters to degrees; if values lower than 0.2 are entered they will be considered as degree and used as such without any conversion.

 

Different grid size, in Easting and Northing direction, can be specified.

 

Replace Dummy with sea level value        

By setting this flag all dummy values (i.e. NaN) will be replaced by the value zero, if the "subtract geoid" flag is not active, or by the ellipsoidal equivalent if the "subtract geoid" flag is active.

 

 

Parameters - Global

 

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

 

Parameters - DEM FTP Address

 

It brings to the FTP section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

 

Parameters - Other Parameters

 

It brings to the general section of the Preferences parameters. Any modified value will be used and stored for further processing sessions.

 

Output Files

 

Output DEM file

Output file name of the extracted and mosaiced Digital Elevation Model. This file is mandatory.

 

_dem        

Extracted Digital Elevation Model, with user-defined projection and grid size, and associated header files (.sml, .hdr).

 

_dem_wgs84_dem        

Extracted and interpolated Digital Elevation Model, with original projection and grid size, and associated header files (.sml, .hdr).

 

_dem_TMP_wgs84_dem        

Extracted and not interpolated Digital Elevation Model, with original projection and grid size, and associated header files (.sml, .hdr).

 

_wgs84_dem_geoid_geo        

Geoid height with original projection and grid size, and associated header files (.sml, .hdr). This file is generated only when the "Subtract Geoid" flag is checked.

 

_W2E_slope

Easting direction slope image and associated header files (.sml, .hdr).

 

_S2N_slope

Northing direction slope image and associated header files (.sml, .hdr).

 

_slope

Combined slope image and associated header files (.sml, .hdr).

These last three files are generated only if the relevant flag is set.

 

Details specific to the Units of Measure and Nomenclature of the output products can be found in the Data Format section.

 

General Functions

 

Exec

The processing step is executed.

 

Store Batch        

The processing step is stored in the batch list. The Batch Browser button allows to load the batch processing list.

 

Close        

The window will be closed.

 

Help

Specific help document section.

 

 

Specific Function(s)

 

None.

 

References

 

None.