# RenderPark User Guide

## What is RenderPark?

RenderPark is a photo-realistic rendering program. You feed it with a 3D model (geometry and material properties). RenderPark then computes either a photo-realistically illuminated 3D model or a high- or low-dynamic range image of the model as seen from a particular view.

RenderPark is different than other renderers in that it uses a physically-based illumination simulation in order to do its job. Because of its physically-based approach, the resulting illuminated model and the images computed with RenderPark will (ideally) be as close as to reality as the input allows. RenderPark is suited for quantitative prediction of the illumination in buildings that have not yet been built for instance. In order to achieve this goal, RenderPark needs physically-based material descriptions of the surfaces in a scene. A light source will be described by its luminous power for instance rather than just a color.

In the remainder of this user guide, we assume that you are familiar with global illumination (radiosity, ray-tracing). Good introductions to global illumination can be found in:
- M. Cohen and J. Wallace, "Radiosity and Realistic Image Synthesis", Academic Press Professional, 1993
- F. Sillion and C. Puech, "Radiosity and Global Illumination", Morgan Kaufman, 1994
- P. Shirley, "Realistic Ray Tracing", A. K. Peters, 2000
- Various ACM SIGGRAPH courses

## Usage

### Summary:

- Start by loading a 3D scene.
- Once loaded, you can "illuminate" it using a radiosity method, or you can generate an image using ray-tracing. RenderPark offers a variety of radiosity and ray tracing algorithms. You can do ray tracing after radiosity, combining the strengths of both. The photon map is an advanced two-pass algorithm in this spirit.
- The illuminated 3D model after radiosity is rendered using graphics hardware. Illuminated 3D models and images can be saved in various ways.
- You can choose a view point and navigate through a scene interactively.
- For a correct display of the results, RenderPark offers advanced tone mapping operators and supports monitor calibration.
- RenderPark can also be used as a batch renderer. or as a plug-in in other applications such as 3D modelers.

RenderPark Screen Shot: Choosing a Radiance Method

### 1. Loading a 3D model

Load a scene by selecting the 'Load Scene' button in the File menu. RenderPark reads files in the Materials and Geometry Format (MGF). A small collection of scenes is provided in the SCENES subdirectory. More scenes are available on the web site.

### 2. Radiosity

Select a radiosity (or better: world-space radiance) method in the Radiance menu (see screenshot above). You can set control options after pressing the 'Control' button. You start/interrupt the computations using the Run/Stop button. Currently available world-space radiance methods are:

- hierarchical Galerkin radiosity with higher order approximations
- stochastic Jacobi radiosity (our favorite radiosity method)
- random walk radiosity
- photon map construction

### 3. Rendering and saving the illuminated model

You can control the way the illuminated model after radiosity is rendered using graphics hardware with the options in the Rendering menu.
The resulting image can be saved using the 'Save image' button in the File menu. RenderPark supports the PPM and TIFF image file formats. Numerous convertors and image manipulation tools exist for these formats.
You can also save the illuminated 3D model after a radiosity computation in VRML'97 format using 'Save Model' in the file menu. .

### 4. Ray-tracing

After a world-space radiance computation (if you did one), a per-pixel (ray tracing) pass can be used to make a very precise image using the current virtual camera. Choose a ray-tracing method by selecting the 'Method' button in the 'RayTracing' menu. You can choose between

- stochastic ray-tracing
- bi-directional ray tracing
- ray casting.

You can control parameters in the panel you get after clicking the 'Control' button. Start/Stop the computations by selecting the Run/Stop button. The resulting image can be saved using the 'Save Image' button. In addition to PPM and "normal" TIFF format, you can also save in in high dynamic range (logluv) TIFF format by specifying .logluv as the file name extension here. The most recently computed image can be redisplayed at any time by clicking the 'Redisplay' button'.

### 5. Interactive navigation

When the program is not busy rendering (indicated with a spray can cursor), you can manipulate the virtual camera by moving the mouse on the canvas window while pressing a button. By default (3-button motion), you

- rotate the virtual camera right/left/up/down by moving the mouse while pressing the left button
- translate the camera right/left/up/down by moving the mouse with the middle button pressed.
- translate the camera right/left/forward/backward by moving the mouse with the right button pressed.

You can also edit, save and restore the virtual camera manually in the 'Camera' menu.

### 6. The photon map

RenderPark now contains a rendering technique called the Photon Map: The photon map is a two-pass method for computing very high quality images of models exhibiting general illumination. It is faster than bi-directional path tracing at the cost of some approximations.

It is a two-pass method:

- The first pass is a viewpoint independent light particle tracing pass, which you perform by selecting the Photon Map Construction method in the 'Radiance->Method' menu.
- The second pass is an enhanced version of stochastic ray tracing, in which the stored particle hits of the first pass are used. In order to generate an image after the first pass, you need to perform stochastic ray tracing with the 'Photonmap specific' Radiance contribution option checked in the stochastic ray tracing control panel.

### 7. Tone mapping

All rendering algorithms in RenderPark require that radiometric intensities be mapped to display colors at the end. The process of mapping radiometric intensity values to display colors is called tone mapping. The 'Tone Mapping' menu offers a variety of tone mapping strategies, allows to brighten or darken images artificially and lets you take advantage of a calibrated monitor.

### 8. Batch rendering

RenderPark accepts numerous command line options. It can be used for batch rendering as well as for rendering into an external canvas window. It can also be controlled using Inter Process Communication. Type 'rpk -help' to see what options are available.