Lucid Introduction

8/2/2019 Lucid Introduction

1/18

An Introduction to LucidShape

Brandenburg GmbH, Technologiepark 19, 33100 Paderborn, Germany

Version 1.10

March 21, 2011

Abstract: This overview article gives an introduction to the basic concept and the mostimportant components of LucidShape.

Table of Contents

1. What is LucidShape? .................................................................................................................... 22. Digital Mock Up for Lighting Products .......................................................................................... 3

2.1. The "Form Follows Function" Paradigm with LucidFunGeo ............................................... 4Macrofocal Applications for Sharp Cutoff Lines ................................................................ 4Poly Curve System Applications for Projector Type Headlamps ........................................ 5Procedural Surface Applications for Structured Profiles ................................................... 6

2.2. Standard and Procedural Surfaces via the Conventional Approach ................................... 72.3. Geometry Creation from LucidShell Scripts ....................................................................... 72.4. Geometry Exchange with External CAD Tools .................................................................... 8

3. "Shape = Geometry + Material" as the Basic Concept in LucidShape ......................................... 93.1. Actor Materials .................................................................................................................. 93.2. Emitter Materials ............................................................................................................. 10

3.3. Sensor Materials .............................................................................................................. 114. Light Simulations ........................................................................................................................ 114.1. Forward Ray Tracing vs. Light Mapping ............................................................................ 114.2. Color Simulations ............................................................................................................. 114.3. The Luminance Camera .................................................................................................... 124.4. The Ray History Sensor .................................................................................................... 124.5. Parallel Simulations ......................................................................................................... 134.6. Light Sources ................................................................................................................... 13

5. Analysis Tools ............................................................................................................................ 145.1. Interactive Ray Trace for Shape Analysis .......................................................................... 145.2. Light Data Analysis .......................................................................................................... 14

5.3. Lens Analysis and Correction ........................................................................................... 156. Night Driving Simulations with LucidDrive ................................................................................. 167. Various Geometry Service Tools ................................................................................................. 17

7.1. Surface Approximation or Interpolation ........................................................................... 177.2. Tessellation ..................................................................................................................... 18

1


2/18

1. What is LucidShape?

LucidShape is a powerful 3D system for computer aided design of lighting (CAL) and opticalproduct function. Its strengths are interactive tools for design, simulation and analysis.

Figure1: Lighting setup with reflector(displayed in 2 independent views with light ray samples) and simulationresult.

Light manipulating geometry ("shapes") can be calculated under optical conditions, anda rapid ray trace algorithm gives a prediction for the intended product's function. Severalexamination and documentation tools for shapes and light data support the developmentprocess. CAD data as well as photometry data can be imported and exported.

LucidShape mainly consists of

The interactive development environment LucidStudio to execute all design tasks andto display and analyze geometry and simulation results. LucidStudio runs under allmodern MS Windows systems. Fig. 1 shows a LucidStudio screen shot. Depending onthe type of data to be displayed and analysed, LucidStudio offers several view types:

Geometry View: For all 2D and 3D geometry (reflectors, lenses etc.)

Light Data View: For light data (photometry data, simulation results).

Tree View: For the hierarchical display of all model objects in a structured tree.

Light Screen View: For the display of light source filament images. Used together withthe interactive raytracer (see Section 5.1).

2


3/18

Message View: For various text messages (object and process information, warnings,errors)

The script interpreter LucidShell serves as a driver language for the LucidShape designsystem. It can be used to perform all tasks through a script procedure written in a C/C++like language. This way, LucidShape can easily be extended. In addition, it can also be

used to customize and extend dialogs and menus in LucidStudio.

The LucidShell language also serves as a data storage format for the LucidShape system.It makes it easy to modify a saved model with any standard text editor.

The language interpreter is available under LucidStudio or as a standalone commandline tool.

Figure 2: A short piece ofLucidShell code and the geometry it produces

2. Digital Mock Up for Lighting Products

In order to make simulations and analysis, a digital mock up for the lighting/optical producthas to be set up, that is, a collection of optical geometry (reflectors, refractors), light sources

and light detectors has to be created. LucidShape supports the setup of such a "opticalscene" in the following ways: Geometry may either be defined interactively within Lucid-Studio, calculated in a shell script in LucidScript, or imported from a CAD file.

3


4/18

2.1. The "Form Follows Function" Paradigm with LucidFunGeo

LucidFunGeo (standing for LucidShape Functional Geometry) is a broad selection of toolsunder LucidShape, allowing to create optical geometry in various ways

1.

One of the particular strengths of many of the LucidFunGeo tools is the ability to generate

geometry directly from optical requirements. For example, for having to compute a freeform reflector which should emit the light in a specific angular direction, one would like tocompute the reflector directlyfrom this lighting requirement, rather than having to generateit from geometric parameters and check whether the optical behaviour is within the require-ments, all this in a possibly tedious process cycle. LucidShape supports this "Form followsFunction" paradigm whenever possible.

Figure 3: Example for the "Form follows Function" paradigm in LucidShape: An LED based signal lampcomputed directly from its lighting requirement (left) and verification of the computed result from simulation

(right)

Macrofocal Applications for Sharp Cutoff Lines

The macrofocal concept2

is a way to create sharp cutoff lines (e.g. for automotive low beam

applications) by designing reflector or lens arrays that use the edge contours of the entire

light source and not simply a point. In the LucidShape Macrofocal Applications, a typicalsetup would require the user to define

1. a planar grid as the base for the geometry array to be computed, and

1Generally,geometry is created in LucidShape as NURBS (Non Uniform Rational B-Splines) curves or surfaces,a highly flexible

mathematical geometry description based on control points which is the most common used in industry.2

The macrofocal concept was first described 1965 in a paper by Spencer et al.

4


5/18

2. the required light function (target range, type of cutoff etc.) for each grid element.

Once the setup is defined, the LucidShape macrofocal solver will compute the desired op-tical array within seconds.

Figure 4: Head lamp design producing sharp cutoff lines with the macrofocal concept. The example showsECE and SAE low beam patterns.

Poly Curve System Applications for Projector Type Headlamps

In LucidShape, Poly Curve Systems (PCS) are lighting setups whose computation is basedon a number of curves with special optical functions. The full setups usually include a re-flector, a shield, a light source and an aspherical lens. PCS systems are used for all kindsof automotive headlamp applications, in particular LED systems.

5


6/18

Figure 5: A poly curve concentrator system with a LED light source.

Procedural Surface Applications for Structured Profiles

Generally, Procedural Surfaces are generated from mathematical operations on curvesand/or surfaces. Based on this principle, LucidFunGeo offers a subset of tools which producesurfaces by procedural operations on profiled curves, resulting in profiled reflectors orlenses for a wide range of specific lighting tasks.

Figure 6: A rotational signal beam reflector generated as a swung surface

6


7/18

2.2. Standard and Procedural Surfaces via the Conventional Approach

But also in cases where the conventional approach of generation via geometric parametersis preferred,you will notbe disappointed: LucidFunGeo offers dozens of standard geometrieslike planes, paraboloids, or ellipsoids. In addition, the conventional creation of proceduralsurfaces like

rotational surfaces by rotating a curve around an axis

swung surfaces by rotating a curve around an axis with a varying radius

swept surfaces by sweeping a spine curve along a profile curve

pipe surfaces by sweeping a circular profile along a profile curve (essential for light pipeapplications)

interpolation surfaces by interpolating surfaces from a skeleton grid of boundary curves

is supported.

Figure 7: A light pipe in LucidStudio and the corresponding dialog

2.3. Geometry Creation from LucidShell Scripts

Most of the geometry generating tools are available within LucidStudio and via scriptingin LucidShell alike. As shell scripting allows parameterization of geometry via standardprogramming structures like loops, scripting may come in handy in cases where large arraysof similar geometries, or very special geometries have to be created.

7


8/18

Figure 8: A two-dimensional array of 5x5 paraboloids, and its generating LucidShell script code using twonested "for" loops.

2.4. Geometry Exchange with External CAD Tools

Geometry which surrounds the lighting fixture (e.g., bezels, support structure, light shields)may sometimes be more easily designed in a CAD system and imported. Or, geometry maybe generated in LucidStudio and exported into a CAD system. LucidShape supports allmajor CAD data formats like IGES, STEP, or 3DM. Data may seamlessly be imported/exportedand situated at their appropriate places by simply pressing a dialog button.

Figure 9: Two rotational paraboloids, a) in LucidStudio and b) in CATIA after having been transferred fromLucidStudio and located at their appropriate positions in a bezel.

8


9/18

3. "Shape = Geometry + Material" as the Basic Concept in LucidShape

The formula "Shape = Geometry + material" builds the basic concept in LucidShape toperform all lighting tasks. Here, material is understood beyond its very physical meaningin the general sense of a (physical) property that is attached to a geometry, determiningits behaviour during simulations.

Three basic kinds of materials are available: actor, emitteror sensormaterials. Becauseany geometry may be combined with any type of material, this concept allows highly spe-cialized setups. Materials may be selected from LucidShape's broad library,or comfortablycreated in LucidStudio according to the user's individual requirements.

Figure 10: The basic principle in LucidShape: Shape = Geometry + Material, Material = Emitter or Actor orSensor

3.1. Actor Materials

Actor materials are used to build objects which passively interact with light rays in thesetup, merely reflectors or lenses. For example, a mirror material may be combined with aparaboloid surface. The resulting shape will then behave like a mirror, i.e. light rays hittingthe paraboloid will behave according to the laws of reflection. Another example is a lensshape that one would build from an inner and outer surface (as the lens's boundaries) plus

a refractive material defined from two media (inner and outer, like for example glass andair). Any ray hitting the lens shape will then be deflected according to Snell's law andtransmitted through the lens according to the physical properties of the material's innermedium.

9


10/18

Figure 11: A lens shape, built from an inner and outer surface and a refractive material with Schott glass asits inner medium.

3.2. Emitter Materials

Emitter materials are used to build objects which emit light rays in the setup, merely lampmodels. For example, a cylinder surface may be combined with an emitter material togenerate a cylinder light source. During simulations, this shape will generate light raysclosely following the emitter material's physical properties (spectral curves, directionalcharacteristics etc.) Note that due to the flexible shape concept, all kinds of surfaces maybe used to generate light emitting shapes.

Figure 12: An emitter shape to model a coil light source, built from a pipe surface (with a helix as base curve)and a Lambertian emitter material.

10


11/18

3.3. Sensor Materials

Sensor materials are used to build objects which collect and store light rays in the setup.In most cases, they will be combined with planar surfaces to store simulation results (forexample in a Lux sensor), to be displayed and analyzed in Light Data Views.

Figure 13: A setup with a planar surface equipped with a Lux sensor material.

4. Light Simulations

Generally, a light simulation is the process of computing a prediction for the light functionof a given lighting fixture by making use of the involved shapes' (resp. their materials)physical properties. A simulation answers questions like: "What will be the light intensitydistribution?" or "What will be the illumination distribution on the surface of interest?"

4.1. Forward Ray Tracing vs. Light Mapping

Several simulation tools are available, which differ mainly in calculation time and precisionof the calculated results. The general forward ray trace simulation based on the MonteCarlo principle gives the best and most precise results for intensity and illumination distri-butions. However, as it relies heavily on the precise calculation of ray/surface intersections,the forward ray trace requires increased calculation time depending on the scene's com-plexity. For the initial design of geometry one needs a fast estimate to see the effects ofgeometry modification. For those tasks, LucidShape's light mapping simulation offers away to calculate light distributions within seconds.

4.2. Color Simulations

Besides single wavelength (monochrome) simulations, LucidShape also allows multiwavelength simulations to detect special color effects which are sometimes caused by re-fraction.

11


12/18

Figure14: Result from a LucidShape color simulation of a low beam lens headlamp. The lens causes a narrowseam of blue and red coloured light above the cutoff line.

4.3. The Luminance Camera

Capturing lit appearance images from an optical system can be very useful for analyzingthe units performance and asthetics. LucidShape's luminance camera is a way to generate

photo realistic3 lit appearance images of any optical component in the scene.

Figure 15: Lit appearance images of a signal lamp, rendered from a simulation with 109

rays.

4.4. The Ray History Sensor

After a simulation, a typical analysis task is to inversely identify shape regions: For an ex-amined region in the simulation result, find out which of the actor shapes' regions are"responsible" for the examined result regions. Here, the LucidShape Ray History Sensorcomes into play. Working like a kind of simulation memory, it records all rays during asimulation to process such queries after the simulation. In practice, one would simply marka region (for example a circle) in the simulation result to get the relevant rays displayed inthe Geometry View.

3of course, the render image quality scales directly with the number of rays in the ray trace simulation.

12


13/18

Figure 16: The Ray History Sensor: Marking a region in the simulation result (right picture) yields the displayof the relevant rays in the Geometry View (left picture).

4.5. Parallel Simulations

As a special feature, LucidShape also allows scheduled parallel simulations on multipleprocessor cores, or even on multiple machines in a local network.

4.6. Light Sources

As indicated in Section 3, simulations usually require actor shapes, sensor shapes andemitter shapes, the latter being supported by extensive libraries containing all importantkinds of light sources (especially LEDs) for various applications.

Figure 17: A D1R low beam light source from LucidShape's light source library

13


14/18

Also, ray files (as often provided by light source manufacturers) may directly be importedinto LucidShape and used as light sources for simulations.

5. Analysis Tools

Depending on the type of view, LucidShape offers several analysis tools.

5.1. Interactive Ray Trace for Shape Analysis

Being one of the outstanding analysis features of LucidStudio, the interactive ray tracer isavailable in the Geometry View. It may be used to investigate the local behavior of reflectorsor refractors by visualization of ray paths traveling through the examined scene. In Lucid-Studio, one can interactively "touch" actor shapes with the mouse pointer. The interactiveray path tracer will then generate the ray bundles which are relevant for the examinedsurface region and make them interact with the shape, i.e. reflect or deflect/transmit them.All this happens in real time, so the ray bundles will dynamically follow the user's mousemovements on the shape. This allows a very detailed examination of a shape's local lightingproperties.

Along with the ray bundle display in the Geometry View, the light source's filament imagesmay be displayed dynamically in the Light Screen View.

Figure 18: Interactive ray trace with a low beam reflector. A special window displaying the correspondingcylinder light source's filament images is updated dynamically with the user's mouse moves.

5.2. Light Data Analysis

Light data may come from simulation results or can be imported from a data file createdin a goniometer measurement of a real lighting fixture. The data may either be a luminousintensity/radiance distribution or an illumination/luminance on a shape. Within LucidStudioseveral tools allow the analysis of light data. Examples are point measurement tables,

14


15/18

gradient calculations, and the viewing of cross sections of 2D light distributions. Also, fil-tering, addition, subtraction, and scaling can be performed on light distributions.

Figure 19: Light data from a high beam reflector simulation and a corresponding test table

5.3. Lens Analysis and Correction

LucidShape's ray deviation analysis tool computes and analyses the light ray deviationscaused by a lens. The deviations may be displayed in various ways in the Light Data View,for example as a checkerboard image visualization. In addition, correction surfaces maybe computed in order to minimize such deviations. An application for this is the computationof visors for motorcycle helmets.

15


16/18

Figure 20: Lens surfacecorrection to minimizeray deviations. Checking the effects with checkerboard images.

6. Night Driving Simulations with LucidDrive

LucidDrive is a night driving simulation tool to evaluate automotive headlamp beam patternsunder conditions as realistic as possible. Used before expensive fabrication and testing,it complements the design tools by allowing an analysis of headlamps with various road

scenes.

LucidDrive runs in an automatic driving mode without a need for interactive control likesteering, accelerating and breaking. One can switch quickly between different lamps,viewing positions, road types and scenes during a simulation, thus receiving an immediateinteractivefeedback. Additionally, it enables direct comparison between different headlampsetups and the resulting quality of their beam patterns in different road configurations.

LucidDrive is available as a stand-alone tool that may be extended to a complex networkbased multi-PC simulator with up to eight screens. A basic version, however, is availablein LucidStudio.

16


17/18

Figure 21: A night driving simulation scene with LucidDrive

7. Various Geometry Service Tools

In addition, LucidShape contains several geometric oriented service tools. Below followsa short sketch of two of them.

7.1. Surface Approximation or Interpolation

A whole set of tools deals with the approximation or interpolation of curves and surfaces.The input point grids or clouds may come from reflector calculation tools or measurements.Once a surface is created, it can be used immediately in a lighting simulation to check theresult of the reverse engineering.

17


18/18

Figure 22: A surface approximated from a point cloud.

7.2. Tessellation

Tessellated geometry offers some interesting advantages over the standard NURBS surfacerepresentation, as for example simplicity in structure (trimming of surfaces is no longernecessary) resulting in a significant speedup of ray trace simulations. As a drawback, Tes-sellation may blur subtle details if carried out with an insufficient number of triangles.LucidShape contains a powerful, flexible and fast tessellator.

Figure 23: Detail from a large optical setup after Tessellation in LucidShape

Lucid Introduction

Documents

Transcript of Lucid Introduction