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Figure 3. Conceptual layout for the 3D Texture raindrop method. Spherical textures are defined on the base surface and then offset into a volume that encompasses both the incoming and outgoing beams
Different precipitation conditions were also modelled using the software’s 3D Texture Feature to define repeating 3D structures on a surface. Spherical textures were created to represent individual drops, and these were then translated up off the base surface into the path of the beam using the z-offset parameter. A simple macro randomly distributed the drops inside a predefined volume surrounding the outgoing and incoming beam paths.
The textures can be any definable shape and the resulting ray tracing is correct, even if the rays never hit the base surface. Jacobsen added: ‘LightTools will let you place millions or even tens of millions of these textures in this way.’ Receiver filters were also used to help model the time sequencing of the detector. Receiver filters are software settings that are associated with a given receiver. Rays are then counted on the receiver or not
depending on the filter settings, allowing you to only display results from a specified source, for instance. You can filter on a given optical path length allowing you to only accept rays in a give time window as you would in an actual Lidar system. You can also use multiple filters in a logic tree where, for example, you only count rays that come from source A and also hit surface B. This capability can result in ‘huge time savings’ in the design phase, according to Jacobsen, who added: ‘This kind of filtering really makes analysing complex systems much easier.’
The Optimizer Tool in
LightTools also features a built-in function for scanning variables across a predefined range, running a simulation and then gathering user-specified data from the simulation results. Once finished, the results are charted and are available to cut and paste into other applications such as Excel.
As a result, the user can easily and automatically scan the target distance through a set of values,
run a simulation at each setting and then record the return flux on the detector. This process is typically completed by hand, but such automation is ‘a real time- saver,’ according to Jacobsen. The work also identified
several other benefits of the LightTools system, which are fully discussed in the whitepaper with the methods used to explore this real-world problem. In terms of next steps, Jacobsen hopes to model a wider range of precipitation, including snow or sleet, more fully evaluate the solar background illumination and investigate different reflective scattering surfaces. But this is the tip of the
iceberg with regards to what LightTools can achieve in our wider, varied world. Jacobsen concluded: ‘LightTools can be used in the design of environmental lidar or lidar for other uses like airborne topography mapping, the design principles are the same or very similar, but currently we are seeing the most activity in autonomous vehicle development.’ EO
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Application in Illumination Design: Analysing lidar return signal strengths for target optical surfaces and atmospheric conditions
This whitepaper aims to show how software can be used to simulate the performance of automotive lidar systems - specifically, the effects on the expected return signal of scattering properties, incidence angles, and atmospheric conditions.
www.electrooptics.com/white-papers
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