Ray tracing

by François de Dardel

Introduction

For those curious: the picture on the left is a synthetic (or "virtual") image created on the Macintosh using Persistence Of Vision (POV) Ray-tracing. The image is built geometrically, using so-called "Constructive Spatial Geometry".

All the objects and other textures or patterns are created and assembled "by hand" using POV. A virtual camera and virtual light sources are then set, and the picture is created ("rendered") by "ray tracing". By moving the camera around, you can take any number of pictures of the same scene.

The real Mac fans will notice that the iMac G4 is a little simplified. The screen itself however is a dump from my own Mac. More about ray-tracing under other pictures, with the new Italian villa, but first have a look at my house.

The house project

This is an exercise with one single picture file and many resulting images. Here, I started (in August 2005) from a file made by Sascha Ledinsky, and I added many details, including the tree, the pavement, the fountain, the bench and the landscape around the house. Then I placed furniture inside the house to take interior views. See the position map to orient yourself and the floor plan to get acquainted with the the house indoors.

Everything is defined geometrically, except the pictures on the walls and the tapestry. There are three source files totalling 144 kB of text to describe the house, its environment and the furniture, plus another 12 kB for the tree adapted from Jean-Laurent Pradel, and 24 kB for the sea plane borrowed from Kurt Bangert. Moving the "camera" around and into the house demonstrate that it is indeed a geometric object and not a series of drawings. I only vary the position of the camera, and the lighting, to get all the images on the right. I also occasionally move around the balloon and adjust the weather fane. I have changed the environment in August 2007, and the island landscape is now somewhat more realistic.

I designed the pavement with individually random-coloured cobblestones.

In the outdoor pictures, there is a little amount of fog, so that the distant objects are not as clear as the close ones. I am not completely satisfied with the results, and hope to do better at a later stage. The POV program is very powerful, and quite complicated to learn. There are hundreds of commands to adjust light, colours, textures, reflection, refraction, and everything is hard coding. Clicking on the close-up of the roof, you will see the arrangement of the tiles, courtesy of Sascha Ledinsky. I would never have found the complicated algorithm used for this purpose, but I learnt from it to make the pavement around the house.

This is the first version, made in August 2005. It had no landscape, was smaller, and empty. The door opened on the wrong side, too... Today, there are many items in the house. I created most of them, but I also borrowed and modified several objects from files made available by the community of POV ray tracers.

I started ray-tracing around 1993 with DKB (by Eduardo Schwan), the ancestor of POV. I am still not a big expert, although I improved a lot through practicing after mid 2005. Several of the pictures made their way to my employer's web pages, which I created early 1998. If anybody has comments or suggestions about these pictures, I will be delighted to read them.

More information on the ray-tracing software and principles can be found in the POV site pages. See also my links page.

With POV Ray-Tracing, you can create a panoramic view that you can then convert to a Quick Time movie. If you have the Apple Quick Time plug-in installed on your computer (it is available for Windows as well as for the Macintosh) you can navigate with your mouse and see the complete picture of the room. You can also zoom in and out. The definition is not quite as good as that of the individual pictures, but I find the effect amazing.

In this view, the camera is located between the glas table and the desk. Move your mouse in the picture on the right.

If you see only an empty frame instead of the panoramic picture, you must download and install the (free of charge) Apple Quick Time plugin.

Here you see the kitchen, the flight of stairs going to the attic, and you have a glimpse to the outside through the open glass door. Also, you can see the shower through the open bathroom door. Here, I have put the camera at the end of the kitchen table.

Move your mouse in the picture on the right. You can also zoom in and out using the + and – signs.

Finally, now that I have changed the landcape (August 2007) we can look around the house and have a better view of the islands. See the general position for orientation. Note that the balloon may change place from a picture to the next.

Move your mouse in the picture on the right. You can also zoom in and out using the + and – signs.

On my Macintosh G4 with biprocessor at 1 GHz (2002), the desk picture is rendered (calculated by the computer) in 3 minutes 17 seconds in a 1024 x 768 pixel size. On my Mac 8500 (1998), it took one to two hours, and on my previous Mac IIci (1993), rendering the same image could take as long as a full day... The image above is a compressed jpeg of 640 x 480 pixels. Here on the left, I have rendered only a detail at a larger scale, and under a slightly different view angle.

To be totally honest, I have borrowed the blue vase from another ray-tracing author (Dan Farmer), the pencil (which I modified) from Jorge Arreguin and the wooden textures from Dan Farmer again and Paul Novak. These are supplied together with the (free of charge) ray tracing software of POV.

So, I only created the other objects: the column, the table, the paperweight, the golden sign with my name, the pencil holder and the picture frames, and assembled them to this picture. It took me about three days (in 1999)...

The plant and the tree — that I have re-used in my house project — is a creation of Jean-Laurent Pradel (1998), that I have slightly modified. There are (in my version) 21 parameters to play with and change the style of the tree. You see thus two examples with different settings. However, it still looks somewhat artificial. On the other hand, it renders quite fast, because the algorithm used to create it is very compact, which does not mean it is simple. The splendid yellow flying boat was created by Kurt Bangert. It is a very faithful reproduction of the Boeing 314 "Yankee Clipper" operated by Pan American between 1939 and 1951. For interest, here are the specifications of the original big plane.

I created the Italian villa based on a painting by Francesco Granacci. See my version and the original, viewed under the same angle. Unfortunately, it is impossible to describe human beings geometrically, and vegetation is very difficult to model, as you can see from the tree, and takes a long time to render. On the left here the wide angle view of the villa. I borrowed the statue from an unknown expert.