Rendering with Radiance

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Nancy Potter
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1 Radiance Overview This section introduces some more information about Radiance and how IES have integrated it into the Virtual Environment. This document is not intended as an exhaustive study of this subject, but as an introduction to some of the concepts. More information about Radiance can be found in the book Rendering with Radiance by Greg Ward Larson & Rob Shakespeare, published by Morgan Kaufmann Publishers. Contents: Introduction The IES View of Radiance Components Luminaires Project Directory Structure Radiance Data Files Radiance Publications Page 1 of 15

2 Introduction Radiance is a software package developed by the Lighting Systems Research group at the Lawrence Berkeley Laboratory in California, USA. Radiance was developed as a research tool for predicting the distribution of visible radiation in illuminated spaces. It takes as input a three-dimensional geometric model of the physical environment, and produces a map of spectral radiance values in a photo-realistic colour image. It can be used to calculate lighting levels (LUX), Daylight Factors or Glare for daylight and/or artificial lighting. Radiance is internationally recognised as one of the leading lighting simulation tools available. IES have been using Radiance over a wide range of commercial projects for many years and to facilitate this work IES have integrated Radiance into the <Virtual Environment>. The latest version of this integration, RadianceIES, provides users with even greater ease of use through its customised Graphical User Interface (known as the <Virtual Environment> Framework), which integrates with all the other IES software packages (SunCast, Apache, etc.). Page 2 of 15

3 The IES View of Radiance The Radiance interface module RadianceIES has now been integrated into the new <Virtual Environment> Framework. This means a greater degree of compatibility between the various modules and more natural interfaces for the user to navigate. From a conceptual point of view the RadianceIES interface can be treated as a stand-alone module (as shown below). A more detailed description of the RadianceIES interface is described in the chapter The RadianceIES Interface. The following figure shows the mechanism that has been adopted as an efficient and effective way to control the manipulation of the necessary data and the creation of images. Page 3 of 15

4 The 3D geometry of the model created by ModelIT is converted by an internal module (mit2rad) which is hidden to the user. Global properties are inherited from the ModelIT database e.g. site data, and default properties are assumed for other data requirements e.g. surface colours, etc. This information is written into three data files the sky file, the map file and the rad file. In RadianceIES the user may manipulate the specific properties that are required. These 3 data files are required by the program oconv, which uses these data files to create the octree file. There are two types of picture file created by Radiance, luminance and illuminance. An illuminance picture can be used to look at Lux values and generate Lux or DF contours, a luminance picture can be used to generate glare indices or as a photo-realistic image. The interface program RadianceIES allows the user to create the two data files, the view file (*.rdv) and the parameter file (*.rdp), that control the image generation program, rpict. The raw image file is filtered and scaled by the program pfilt to create the picture file (*.pic). The interface is designed to make things as easy as possible for the user to create images by making default assumptions where possible. Radiance can be categorised as a ray-tracing algorithm, which tracks rays of light backwards from the eye and into the scene. This contrasts with the radiosity technique where the exchange of energy between surface patches is calculated. Page 4 of 15

Components The Component Modeller can be used to add components (3D objects used to represent elements within a zone, e.g. desks, chairs, people, etc.) into the model.

5 Components The Component Modeller can be used to add components (3D objects used to represent elements within a zone, e.g. desks, chairs, people, etc.) into the model. The relationship between RadianceIES and the Component Modeller is as follows: The Component Modeller updates the model with the user defined components from the component library (components may be imported from standard libraries or other projects). These are filtered by an internal module (com2rad) and input to the Radiance module oconv. Subsequent steps in the process are the same as the standard Page 5 of 15

6 scenario. Luminaires The module Light-Pro can be used to add luminaires into the model. The relationship between RadianceIES and Light-Pro is as follows: Light-Pro updates the model with the luminaire data selected by the user from a database. The selected luminaires are converted to the IESNA data format, which are then converted by the program ies2rad into a format usable by Radiance (*.rad and *.dat). An extra input file (*.lum) is added to the oconv input stream, which defines the luminaries, which are active in this simulation. If no daylight is required for this simulation then the sky file is omitted from the input stream. Subsequent steps in the process are the same as in a normal daylight simulation. Page 6 of 15

Project Directory Structure One problem with running multiple applications or multiple simulations is keeping track of all the required data files.

7 Project Directory Structure One problem with running multiple applications or multiple simulations is keeping track of all the required data files. It is strongly recommended that a specific project directory be created for each model even where one model may be a variation on another. This allows the subdirectories (or folders), which are automatically created by ModelIT, to be unique to the particular model and avoids confusion between data files. All files associated with the Radiance view of this project - picture files, octree files, etc. are stored in the Radiance sub-directory, and is the default location when looking for files. A description of the use and contents of each of these file types follows in the next chapter. Files which use the root project name are used as default instances of the file type when creating images interactively, e.g. for the project office.mit, the files office.map, office.rdv, office.rdp, etc., are all created with default settings and are updated automatically when the relevant tabs are updated. Page 7 of 15

8 The master file is the *.mit file which is located at the Project directory level. This file contains the 3D description of the model and other information relevant to the model. It is a binary file and can only be accessed through the ModelIT framework and the applications which run under the framework i.e. RadianceIES. Also at this level is the Component Library file, the *.mcl file (it is possible to access components from other models). Certain other files store information which is used by Radiance and other applications, these are summarised in the table below. *.mtd *.mcl Apache\*.df Apache\*.loc Apache\*.mat Apache\*.pdb Apache\*.pro Apache\*.wea ModelIT template file. Component Library file. Detailed constructions. Location file. Material definitions. Profile descriptions. Profile group descriptions. Weather file. Note that when a model has to be transferred all these files are required. To help with this there is an Archive option in the main <VE> pull-down menu which allows the user to create a single compressed file of all the required model data. This is also the most efficient way for sending models by . Page 8 of 15

9 Radiance Data Files The following data files may be found in the Radiance sub-directory: *.sky *.map *.rad *.rdv *.rdp *.oct *.raw *.pic *.log *.bat *.ies *.dat *.gmf *.glr Sky file. Materials properties file. Converted or native Radiance geometry file. View parameter file. Accuracy parameter file. Octree file. Raw data file. Picture file. Log file. Batch file. IESNA luminaire file. File associated with luminaire data. Pre-defined material properties file. Glare file Sky File (*.sky) Contains information which affects the sky conditions -date, time, site and sky. This file contains a call to the Radiance program gensky, which takes the date and time as parameters ( ) and also site data ( -a ). There are 7 standard sky conditions available: 5.+s sunny sky 6.-s standard clear sky 7.-c standard CIE overcast sky 8.+I intermediate sky with sun 9.-I intermediate sky without sun 10.-u uniform cloudy sky 11.10K_cie CIE overcast sky fixed to 10K Lux Page 9 of 15

10 Map File (*.map) Contains data on the patterns and materials that are assigned to the constructions in the model Converted Geometry File (*.rad) This file contains a geometrical description in a form that Radiance can interpret. If luminaires and/or components are also to be included in the simulation additional data files containing this information are created. In the current setup a parent file which references all these files is created View Parameter File (*.rdv) This file contains the parameters for a particular view - the type of view (perspective/plan), the eye position (x, y, z), the viewing direction, angles of view, etc. This file is created when the user saves the contents of the Eye view position dialog items. When the user creates images interactively without specifically saving the view parameters a file with the same root name as the project is created. This file is defined as a parameter to the rpict module, which generates the radiance image Page 10 of 15

11 Accuracy Parameter File (*.rdp) This file contains the simulation parameters that determine how accurate the simulation will be - ambient bounces, etc. This file is created when the user saves the contents of the Accuracy dialog items. When the user creates images interactively without specifically saving the simulation parameters a file with the same root name as the project is created. This file is defined as a parameter to the rpict module, which generates the radiance image Octree File (*.oct) A binary data file created by oconv and read by rpict, contains the octree data structure, which is used to speed up the ray-tracing algorithm. If the resultant image is a luminance image the octree file is used in the calculation of glare. For illuminance images the octree file can be discarded when the image has been created. An octree is a data structure that subdivides a cubic volume of space into eight sub-cubes, each of which may be subdivided into eight subcubes, and so on recursively. This data structure is created by the program oconv and is used to speed up ray intersection tests on the scene. This data structure is stored in the octree file. Page 11 of 15

12 Raw File (*.raw) This is an intermediate picture file created by rpict and filtered and scaled by pfilt to generate the final image. It is deleted by the batch job after the filtering process and is only found if the batch process is interrupted. It has the format and structure of a picture file. The file is created at four times (2 by 2) the picture size as defined in the Eye view position tab. The eventual size depends on the aspect ratio derived from the horizontal and vertical viewing angles (or width and height for a plan view) Image File (*.pic) The final simulated picture, a binary file written in a customized format. Created by pfilt from the raw file as the final step of the batch process, which creates the finished image. Depending on the simulation parameters can be either an illuminance or luminance image. Luminance images are used to generate glare and illuminance images are used to generate Lux values and Lux contours (and DF contours). The first image to be created has the root project name (e.g. model.pic) and subsequent images have a number appended to the root name (i.e. model1.pic, model2.pic, etc.). If images are deleted then the number sequencing may be out order, it is left to the user to rename the images Page 12 of 15

13 if required. Note that the image list in the View images tab sequences the images in the order they were created. Contour images have the labels _LC or _DF appended to the name, or if more than one contour image is created then additional numbers will be added e.g. _LC1, etc Log File The file Radiance.log keeps track of the progress of the processes involved in generating an image (this file is used to update the progress bar). Any warnings and errors are also written to this file. The file is written in append mode and it is left to the user to delete it as required Batch File (*.bat) This file is used to piece together the various files used to generate a simulation (see diagram on page 2). There are two contexts in which this occurs - when the user interactively creates an image from the Create image tab, and when the user assembles batch processes from the Files/Queues tab. In the Create image tab this process is concealed from the user and the files used are given default names (using the root project name), which are automatically updated from the current settings Page 13 of 15

14 IESNA Luminaire File This file conforms to the standard description of a luminaire as defined by the Illuminating Engineering Society of North America. It combines the data for the candlepower distribution of the luminaire with miscellaneous other data items e.g. luminaire dimensions. This file is written out by LightPro. The *.ies file is converted by the program ies2rad into a format usable by Radiance (the *.rad file and the *.dat file). Page 14 of 15

15 Radiance Publications Grynberg, A. Validation of Radiance, Lawrence Berkeley Group, July Ward, G., A Contrast-Based Scalefactor for Luminance Display, Graphics Gems IV, Edited by Paul Heckbert, Academic Press Ward, G., Measuring and Modeling Anisotropic Reflection, Computer Graphics, Chicago, July Ward, G., The Radiance Lighting Simulation System, Global Illumination, Siggraph '92 Course Notes, organized by Paul Heckbert, July Ward, G., F. Rubinstein, R. Clear, A Ray Tracing Solution for Diffuse Interreflection, Computer Graphics, Vol. 22, No. 4, August Page 15 of 15

IES <Virtual Environment> Tutorial RadianceIES (Version 6.0)

IES <Virtual Environment> Tutorial RadianceIES (Version 6.0) IES Tutorial RadianceIES (Version 6.0) Introduction In this tutorial you will use RadianceIES, IES s 3D lighting simulation tool, to perform luminance and illuminance lighting simulations.