<< Click to Display Table of Contents >> Navigation:  »No topics above this level« General Tools - Digital Elevation Model Extraction - ACE

Purpose

 

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

 

Technical Note

 

Before executing this functionality, the ACE compressed files must be manually downloaded from the internet and decompressed within the ACE_DEM_DIR in the default work directory. Note that the specific environment variable (i.e. ACE_DEM_DIR) can be set in order to store the Digital Elevation Model tiles in different user defined folders.

 

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.

 

With respect to previous versions, the latest ACE GDEM is known to provide improved resolution and accuracy over large parts of the globe and especially over Africa and South America.

 

Input Files

 

Optional Reference Slant Range Image

Input file(s) name(s) 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 the X dimension 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 the Y dimension 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.

 

Subtract Geoid

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.

 

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.