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<< Click to Display Table of Contents >> General Tools - Point Gridding |
  
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<< Click to Display Table of Contents >> General Tools - Point Gridding |
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Purpose
An existing DEM in Point Cloud form (Shapefile), previously generated with SARscape, OPTICALscape, or composed by XYZ information can be converted into a raster product.
Technical Note
The process initially exploits the information provided by the respective DEM/DSM generation modules provided in OPTICALscape and SARscape to apply both a knowledge-based and an accuracy-based sample selection. This is imposed by a minimum proximity radius between points which is a constraint of the used interpolator. The choice strategies vary depending on the type of process:
Optical Data
In the case of Optical data, the information contained in the shapefile consists in the Feature Type (see the "OPTICALscape>DSM generation module" for the identifiers), matching cross-correlation and reliability index. Exploiting the knowledge about stereo-optical matching, an edge or point feature will be always chosen rather than a grid point. The choice between identical features is driven by cross-correlation and reliability index.
SAR Data
The choice will be data-driven, the excluded point will always be the one showing the worst precision.
XYZ Data
The choice will be ordering-driven, the excluded point will always be the one following the inspected point.
The final step will be performed exploiting a modified 2D Shepard local interpolator using Thin Plate Radial Basis Functions, the local RBF support will be automatically set. The approach is inspired by the one proposed by Lazzaro D. et. al., the RBF function is given in Numerical Recipes. Two parameters have to be set by the user, namely the number of nearby points on which to fit the RBF function and the number of nodes defining the radius of influence of the computed interpolant. These two values are usually set to 13 and 10 by default respectively.
Two additional steps can be performed, namely a Mean Filtering and a Relaxation interpolation. The former in order to smooth eventual spikes and the latter to provide a continuous surface without holes.
Input Files
Input Shape File
File name of the input point cloud. This file is mandatory.
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.
Note that the input has to be in the same cartographic system as the output.
Parameters - Principal Parameters
Input Type
This flag must be set to define the input type of the point cloud DEM, the choice is given between:
•SAR, if the corresponding input is an interferometric DEM (necessarily generated with SARscape).
•Optical, if the corresponding input is a stereo DEM (necessarily generated with OPTICALscape).
•XYZ, if the corresponding input is a DEM generated outside the SARscape/OPTICALscape ecosystem. The coordinate ordering has to follow the description, hence: X (longitude), Y (latitude), Z (altitude).
Number Of Nodes
Number of nodes defining the radius of influence of the interpolant.
Number Of Coefficient Points
Number of nearby points for the fitting on each node.
Grid Size
The pixel spacing of the output DEM. This value is mandatory.
Relax Interpolation
Set this flag if a final relax interpolation step has to be executed in order to fill eventual holes..
Mean Interpolation
Set this flag if a mean filtering on a regular grid has to be executed.
Mean Window Size
The size of the window for mean filtering. This value is set as 3x3 by default.
Interpolator
The choice is given between:
• Radial Basis Function (RBF).
• Inverse distance weighted Least Squares (LS).
Point Cloud Filtering
Set this flag if the cloud shows evident noise aberrations that you wish to mitigate. The output point cloud will include less points than the input, single isolated points will be eliminated. The Filter radius and Points in radius parameters must be set in accordance with the density of the input point clouds (how many points should be in that radius).
Filter Radius (m)
The radius for the point cloud filter.
Points in radius
The number of points to consider for the given radius in the point cloud filter.
Interpolation Distance Constraint
Set this flag if you wish to constrain the interpolation to a certain distance from the point observations. This will mitigate the edge effect of the interpolator for sparse clouds.
Interpolation Distance Multiplier
Set this flag if you wish to constrain the interpolation to a certain distance from the point observations. This will mitigate the edge effect of the interpolator for sparse clouds.
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 - 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 File
File name of the output combined Digital Elevation Model. This file is mandatory.
_dem
Fusion resulting Digital Elevation Model with the corresponding header files (.sml, .hdr).
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.
Task, SARscapeBatch object, SARscapeBatch script example
References Lazzaro D., Montefusco L.B., Radial Basis Functions for the multivariate interpolation of large scattered data sets, Journal of Computational and Applied Mathematics, 140, pages 521-536, 2002. Numerical Recipes. The Art of Scientific Computing, 3rd Edition, 2007.