SAR Simulator

Purpose

The SAR Simulator tool allows importing 3D models from most of the commonly used 3D file formats and applying simple manipulations on them and parametrize the relevant materials through a series of SAR-specific parameters.

Note: The position of each single panel (Floating Window, Selected Model Info, Simulation, Materials) can be changed by dragging and dropping the specific window.

Functionalities - File

New

Resets the scene removing all the loaded objects.

Open

Load a file in .ovo format. If a file is already loaded it will be overwritten.

Reopen last file

Resets the scene to the last saved version.

Save

Save the current scene in .ovo format which contains materials, 3D elements and transformations are retained.

Note: It is mandatory to save the project before to run the simulation process.

Save as

Save the current scene in .ovo format. Materials, 3D elements and transformations are retained. It also allows specifying a name for the saved file.

Import

Load a 3D file from a format supported by Assimp1, various parameters can be edited if the advanced options are enabled:

Advanced Options:

•Gen smooth normals: If enabled, it allows specifying a maximum angle for the normal smoothing algorithm. Normals exceeding this limit are not smoothed

•Triangulate: If enabled, it splits up faces with more than 3 indices into triangles

•Fix infacing normals: If enabled, it determines which meshes have normal vectors that are facing inwards and inverts them

•Find invalid data: If enabled, it searches all meshes for invalid data, such as zeroed normal vectors or invalid UV coordinates and removes/fixes them

•Validate data structure: If enabled, it validates the imported scene data structure. It checks that all indices are valid, all animations and bones are linked correctly, all material references are correct... etc

•Joins identical vertices: If enables, it identifies and joins identical vertex data sets within all imported meshes

•Sort by PType: If enabled, it moves line and point primitives to separate meshes

•Make left-handed: If enabled, it converts all the imported data to a left-handed coordinate space, i.e. +X points to the right, +Y points upwards, and +Z points away from the viewer

•Flip winding order: If enabled, it adjusts the output face winding order to be clockwise. The default face winding order is counter clockwise

•Flip UVs: If enabled, it flips all UV coordinates along the y-axis and adjusts material settings and bitangents accordingly

•Pre-transform vertices: If enabled, it removes the node graph and pre-transforms all vertices with the local transformation matrices of their nodes

•Move objects to ground: If enabled, any empty space/offset between the lowest vertex and the horizontal plane is removed to lay the loaded model on the ground

•Rescale within 100 m: If enabled, the loaded content is scaled down to fit into a bounding sphere of 100 m of radius. The scaling is applied only if vertices outside such bounding sphere are identified

•Reset XForm: If enabled, transformations to the scene objects are directly applied to their vertices and the local model matrices are set to identity

Merge

Load in the current view a 3D scene from a format supported by Assimp1 or a .ovo file.

Note: Advanced options are not applied to .ovo files.

Load Rays

Load rays computed by the simulation if available.

Reset Rays

Reset the rays previously created or imported.

Settings

From this panel it is possible to define the default Input, Output and Working directory. The user can also set the OpenCL platform and device used for the simulation process.

In the style section the user can decide weather to activate the dark mode while in the 3D viewport section the user can adjust the Light intensity of scene by inserting a certain value or by moving the cursor along the ''virtual slider''.

Quit

Exit from the application.

Functionalities - View

Reset

Reset the view to its original position.

Refresh scene parameters

Refresh scene parameters once the user has applied geometry edits (translation/rotation/scale) on the model.

Functionalities - Sensor

Add

Add a sensor after specifying the needed parameters.

Delete

Delete a previously added or imported custom sensor.

From SML

Add a sensor from an sml file.

Functionalities - Help

About

Details on the software version.

Documentation

It opens the SAR Simulator Help document.

Force license unlock

Unlock the SAR Simulator license; it may happen that, for any reason, the simulation process get unexpectedly interrupted during the simulation execution, in such conditions the license consumed by SAR Simulator might remain locked and no further simulations can be performed.

Functionalities - Main window

Main Panel

This panel allows visualizing check the 3D model.

•Show grid
This parameters allows turning off and on the grid lines.

•X-ray lines
This parameter allows switching off and on the X-ray plane that crosses the objects.

•Wire frame
This parameter allows enabling or disabling the visualization of the elements that compose the 3D model.

•Show normal
This parameters allows displaying the the orientation of the objects in various colors. Object with the same orientation have to have the same color.

•Face culling
This parameters is used to validate the 3D model and check if there are back-faces not correctly built. If the model is correctly built there should not be visible differences when enabling or disabling this option.

•Rim Lighting
This parameter allows highlighting objects contours.

•Bound to local axes
This parameter allows bounding the selected object to a certain axis during the translation, rotation or scale.
Set the Translation and Rotation step to fix, then check the Snap to grid box to enable the use of the configured steps.

The “Invert” button allows adjusting those objects that do not have the right orientation.

Scenegraph

This panel lists the structure of the 3D scene currently loaded in the editor. For each geometry, it is possible to enable/disable its visualization (by checking/unchecking the Visible flag) and to select/unselect one or more objects (by checking/unchecking the Selected flag).

This panel is useful for selecting little objects within the 3D scene or objects that might be hidden by other ones and difficult to select via standard mouse/keyboard interaction.

Note: To select multiple objects at once, hold the ''Ctrl'' button and left click to make a rectangular selection. Right click to deselect the selected objects.

Materials

Material_#

Name of the new material added by the user. The name can be edited by clicking on the Edit name button.

RGB color

A color in RGB format can be specified for every material, this same color will be used for the classification output.

Metallic

The materials of the objects can be of two types, metallic or dielectric. By metallic we mean a perfect electrical conductor (PEC) that fully reflects the incident energy. This type of material is suitable for modeling artificial objects. To apply the metallic property to an object in the scene, the slider must be set to the right. The surfaces on which the objects are placed are instead dielectrics modeled by the dielectric constant and by the roughness. To set the material of the background to dielectric, the slider must be set to the left.

Traced

This parameter specifies if a material must be included in the classification file or not. Untracked materials are all grouped in the untraced class.

Dielectric

When a material is set to metallic, the dielectric constant must be set. This number must be greater than one. The larger the number the more power is reflected by the surface. In case the material is set to metallic, the dielectric parameter value is ignored.

Standard Deviation

The surface height standard deviation expresses the roughness of the background. This number must be greater or equal to zero. The larger the roughness with respect to the sensor wavelength, the more power is received directly from the background. A standard deviation equal to zero means that the background is completely flat and the incoming rays will be reflected only in the specular direction. On the other hand, when the standard deviation is comparable with the sensor wavelength, the rays will be reflected in all directions. In case the material is set to metallic, the standard deviation parameter value is ignored.

Absorption

This parameter controls the percentage of power absorbed from the incoming ray.

Edit name

This button allows editing the material name, the same name will be used in the classification produced by the simulation if the traced parameter is set.

Delete

This button allows deleting the material from the list.

Apply to selected

This button allows applying a material to a previously selected objects of the 3D model.

Add

Add a material after specifying the needed parameters.

Add from template

Add a material after specifying the needed parameters.

Simulation

The sensor parameters needed for the simulation can be automatically selected by choosing the sensor from a list. Each sensor has also one or more acquisition modes (e.g. stripmap, spotlight). Each sensor together with its acquisition mode determines the wavelength, the pixel resolution and pixel spacing in both azimuth and slant range. It is also possible to specify these parameters manually by creating a custom sensor.

General simulation params

•Ground range extent
This parameter controls the length of the scene in ground range. The ground azimuth extent will be equal to the ground range.

•Incidence angle
This parameter controls the angle of the impinging rays with respect to the vertical. This angle corresponds to the starting angle in case of a batch run.

•Rotation angle
Specify by how many degrees the loaded 3D scene is rotated in the simulation around its vertical axis centered at the scene center (where the azimuth and range lines cross in the editor). This parameter is useful to easily generate simulated images of one same target under different rotation angles without needing to explicitly select all the elements of the scene in the editor and rotating them manually. The specified rotation angle does not modify the file content of the scene but dynamically rotates its elements at runtime and only for the simulation being currently executed.

•Squint angle
Specify by the angle between the flight and the look direction.

•Number of bounces
This is the maximum number of reflections that will be considered in the simulation.

•Number of passes
This parameter controls the number of iterations of the path tracing algorithm. At each iteration an ensemble of electromagnetic rays, generating a wavefront, illuminates the scene. The position of the rays is slightly displaced at each iteration. In this way, running a larger number of iterations will increase the probability of illuminating the fine details in the scene.

•Dec. factor
This parameter controls the number of rays to save in the corresponding .ovo file. The higher the value the lower the amount of rays saved.

•Noise level mult.
The noise level multiplication factor is used for thresholding in connection to the generation of the classification outputs. The noise floor of the selected sensor is multiplied by this factor and only signals with an intensity higher than the resulting intensity are considered during the generation of the classification outputs.

Batch (+) and RCS (*) params

•Final inc. angle (+)
This parameter specifies the final incidence angle considered by the batch process.

•Inc. angle step (+)
This parameter specifies the increment for the incidence angle at each step.

•Final rot. Angle (+/*)
This parameter specifies the final rotation angle considered by the batch process.

•Rot angle step (+/*)
This parameter specifies the increment for the rotation angle at each step.

•Tilt (*)
This parameter specifies the inclination of the scene with respect to the satellite incidence angle.

It must be specified that the initial angle for incidence and translation are the ones set in General Simulation params.

Output dir

Define the output directory.

Root Name

Define the root name of the output files.

Tick the boxes to generate all additional files required for the simulation, including those for Bounce and Materials, Silhouette, Shadow mask, Bounding boxes and Conversion slant2ground.

Run

Click on this button to run the Simulation process.

Run batch...

Click on this button to run the Simulation process. The process will use as starting parameters the ones defined in the General simulation params panel, and as final parameters the one defined in the Batch params panel.

Run RCS...

Click on this button to run the RCS Simulation process.

Note:

•Before running a new simulation it is necessary to save the edits made on the 3D model

•Before running a new simulation it is necessary to close the command prompt simulator.exe

Measurements

This panel allows having certain measurements within the simulator as well as to create distance measurements with the cursor.

Scene Extend

Click on this toggle to get the dimensions of the bounding box that includes whole scene.

Traced objects extend

Click on this toggle to get the dimension of the bounding box that includes the traced objects.

Point2point

Indicate the point with the cursor where you want to take a measurement, press 'p,' move the cursor, and then press 'p' again. The simulator will provide the measurement of the segment in meters, its projection on the ground, and the height above the ground.

Output Files

The output files generated by the Simulation process are stored below the path defined by the user in the Output dir tab.

customname: This file represents the simulated SAR image in slant-range coordinates, considering the 3D model and the parameters set by the user. Upload this file by clicking on the Load SAR Image button.

Classification output

•customname_bounces: This layer shows the number of total bounces that determined the final value for traced pixel of the scene. This information is useful to identify which final image contributions are coming from direct returns or double, triple, and multiple bounces between the radar signal and the 3D scene. To load such content in the SAR Viewer, click on the Load Classification entry from the File menu and select the proper file.

•customname_layover_shadow_mask: This layer highlights with different colors the areas subjected to geometrical distortions effects, such as Layover (in red) and Shadowing (in blue). To load such content in the SAR Viewer, click on the Load Classification entry from the File menu and select the proper file. Currently, only shadowing effects are simulated and stored in this file.

•customname_materials: This layer colorizes the radar signal with the color of the material that mostly contributed to its total intensity. Only materials with the tracing flag enabled are taken into account. This information is particularly useful for image interpretation, as it helps understanding from which scene objects specific echoes have been generated. To load such content in the SAR Viewer, click on the Load Classification entry from the File menu and select the proper file.

1 https://github.com/assimp/assimp/blob/master/doc/Fileformats.md