Help Content > Interferometry Module > Stereo-Radargrammetry > 3 - Shift to Height Conversion and Geocoding

Purpose

The absolute calibrated shift is re-combined with the synthetic shift and it is converted to height and geocoded into a map projection. This step is performed in a similar way as in the geocoding procedure (Basic module), by considering the Range-Doppler approach and the related geodetic and cartographic transforms. The fundamental difference with the geocoding step is that the Range-Doppler equations are applied simultaneously to the two antennae, making it possible to obtain not only the height of each pixel, but also its location (Easting, Northing) in a given cartographic and geodetic reference system.

As result of this step also the coherence image is geocoded.

Technical Note

The shift-to-height conversion is performed with a forward transformation. The calculated X, Y, Z Cartesian coordinates (and thereafter map coordinates) are transformed into the coordinates of the output DEM exclusively using a Nearest Neighbor approach.

Two files are generated in this step, beside the Digital Elevation Model and the geocoded coherence image, for a further use in the data mosaicing. They are:

- Precision, which is derived from parameters such as cross-correlation, baseline and wavelength. It provides an estimate (i.e. standard deviation value) of the measurement precision. The higher this value the lower the measurement precision. The formula used for the precision calculation is:

precision_dem

- Resolution, which represents the pixel resolution in ground range, that is:

pixel spacing slant range

sinϑ

where γ is the intensity cross-correlation, λ is the wavelength, R is the slant range distance, ϑ is the local incidence angle.

- Spatial Wavelet Size

The Height Wavelet size, expressed in meters, define what is kept of the residual topography estimated from processing data resolution till the specified resolution value. It removes the low pass distortion under the set resolution value by using wavelet decomposition.

- Data Interpolation is intended to assign a specific value to the dummy (NaN) pixels. The "Relax Interpolation" model is represented by a soft surface, which is adapted to the dummy surrounding area. The algorithm, which is based on the solution of the heat transfer equation (Poisson equation), uses known height values to reconstruct at the best the unknown topography; for this reason it is optimally suited to interpolate small zones, especially where abrupt morphological changes (i.e. steep slopes) are not present.

- Generate Shape format allows representing the DEM as a point cloud. This procedure is intended to preserve the actual pixel value without applying any interpolation, which is the case of the raster output. This format is the one to use as input for the Point Cloud DEM Fusion and for the Point Gridding. It can happen that the .shp and the .dbf become very large when there are a lot of valid points.

Input Files

Coherence file

Name of the coherence image (_cc). This file is mandatory.

Input Range Shift File

Name of the Shift file in range direction (_dr). This file is mandatory.

Range Synthetic Shift File

Name of the synthetic shift file in range direction (_rg_sint). This file is mandatory.

Reference File

File name of the multi-looked Reference Intensity data (_pwr). This file is mandatory.

Secondary File

File name of the multi-looked coregistered Secondary Intensity data (_pwr). This file is mandatory.

Output Root Name

Name of the output root. This file is optional.

DEM/Cartographic System

Output Projection

The following parameters are compulsory to define the Cartographic System:

State

Definition of the country or general projection systems.

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.

Ellipsoid

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

Hemisphere

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

Zone

Definition of the zone. 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.

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

Cross Correlation Threshold

If the correlation value is below this threshold, then the window is not used for the shift estimate.

Spatial Wavelet Size

Generate Raster format

By setting this flag the DEM is generated in raster format.

Generate Shape format

By setting this flag the DEM is generated in vector (.shp) format.

Generate Las format

By setting this flag the DEM is generated in Las format.

Output Type

Allows the use to choose between an output DEM with ellipsoidal heights (default) or heights over the geoid. The geoid type can be chosen in the next flag.

Geoid Type

By setting this flag it is possible to choose the geoid model (default: EGM96) used for geodetic heights in case "Ellipsoidal and Geoidal" is set in the previous flag.

Grid Size

The grid size 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 (X) and Northing (Y) direction, can be specified.

Mean Window Size

The mean filtering of the output height image is carried out. The window filter size must be specified. If zero is entered, the mean filtering is not applied. This filter is applied after the execution of the interpolation steps. The mean filtering is performed only on the Digital Elevation Model output.

Interpolation Window Size

The dummy values in the output file are interpolated. The interpolated value is the average of the valid values in a window of the size specified. If zero is entered, the interpolation is not applied; it is suggested to avoid setting this value to zero (see Technical Note).

Relax Interpolation

By setting this flag the relax interpolation is carried out. This interpolation is applied only to the Digital Elevation Model output.

Dummy Removal

By setting this flag the output geocoded files will be automatically resized in order to remove the dummy area exceeding the frame border.

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 - Geocoding

It brings to the geocoding 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 Root Name

Name of the output root. It is mandatory.

_dem

Digital Elevation Model with the associated header files (.sml, .hdr).

_dem.shp

Digital Elevation Model in shape format and associated header files (.sml, .hdr).

_cc_geo

Geocoded coherence with the associated header files (.sml, .hdr).

_precision

Estimate of the data quality with the associated header files (.sml, .hdr). This file is used during the Digital Elevation Model mosaicing (Tools).

_resolution

Spatial resolution based on the local incidence angle with the associated header files (.sml, .hdr). This file is used during the Digital Elevation Model mosaicing (Tools).

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.

The window will be closed.

Help

Specific help document section.

Specific Function(s)

None.

Interferometry - Stereo Radargrammetry - 3 - Shift to Height Conversion and Geocoding

Interferometry - Stereo Radargrammetry - 3 - Shift to Height Conversion and Geocoding