Workshop Notes 

Workshop 9
4 November 2003  

PARTICLE TRACING

See handout on line on particle tracing:

http://archweb.arch.virginia.edu/~ejm9k/arch541/Handouts/render/ptrace.html

Part I: Particle Tracing Setup

  1. copy directory arch541/read/ptrace
  2. go to utilities > saved views:  apply pers1 (perspective without walls)
  3. tools > visualizations > rendering

 

  1. global lighting (sun icon):  turn off ambient/flashbulb/solar lights for particle tracing.

 

 

  1. define light (light bulb icon):  see lights listed and values; lumens:  light energy rendered in particle tracing.

  1. settings/view attributes/constructions on … see two point/two spot lights.
  2. settings/view attributes/constructions off … be sure to turn off constructions prior to rendering.
  3. tools > visualizations > query illumination (cube w/ question mark icon):  gives a continuous reading of energy output.

 

Part II:  Particle Tracing Settings

Interface > Show Advanced Settings – shows the extended Dialog Box for Particle Tracing

 

1.         Action - current, new, augmented solutions; Create a new solution each time you change the lighting conditions in the model.

2.         Particles Settings - number of particles to shoot (begin 1 mil)

3.         Maxmium Bounces - number of times to bounce each particle (avg 100)

4.         Illuminate Both Sides - Turn off if non-illuminated surfaces are not to be rendered (typically on)

5.         Ray Trace Direct Illumination - Alleviates mulitple shadows computiung shadows from light sources not reflected light - (typically off as disrupts realism)

6.         Mesh Settings - Smooth, smaller values produce sharper shadows, but can introduce noise.  Higher values produce smoother shadows, but can be blurry if value too high.

7.         Mesh Detail - resolution of rendering mesh, higher values produce more accurate results at greater cost in computational time.

8.         Minimum Mesh Detail - in Master Units, specifies minimum size of smallest feature visible in solution (typically leave this off)

9.         Display Mode- Renders result either in photorealistic image (raytrace), illuminance  (energy hitting surface “incoming”) or luminance  (energy reflecting from surface).

10.             Brightness Multiplier – Changes the aperature of the camera to receive more or less light.  This setting does not change the light definitions.

 

 

Action

Use old, update, or generate new solution., save solution

Particle Settings

# particles to use (1 mil)

Maximum bounces

# times bounce (100 avg)

Illuminate both sides

Sometimes surfaces may be non-illuminated (best to default this on)

Ray trace direct

Will alleviate multiple shadows, saves time, not good idea to use this in general

Meshing settings smoothness

Breakdown of mesh to effect smooth surf – noise to smooth

Mesh detail

Level of resolution at key places – higher no. -> higher quality

Min mesh setting

Higher # improves perform at low resolution

Display mode

Visual, luminance (outgoing),illuminance (incoming)

Raytrace final display

Render using raytracing.

Brightness overlay

Aperature.

 

 

Example:

Action: create new solution

Use 1 million particles

Max bounces: 1 million

Illuminate both side surfaces

Ray trace direct illumination (off)

Material Receives/Reflects light (always)

Meshing settings (Smoothness 3, Detail 3)

Min mesh spacing (off)

Display mode: visual/color

Raytrace final display (on)

Wiremesh overlay (off)

Brighness multiplier (as is)

RENDER

 

Change display mode to luminance and then illuminance. 

     Action: Display current solution

     RENDER.

 

Change lights:  Add sunlight on.

      Action: Create new solution for each new lighting condition.

      RENDER.

 

Change Brightness multiplier: 

Lower Brightness multiplier: (0.16)

            Sample hot spot – alt option.

            RENDER.

 

Add background image (doesn’t really effect energy solution)

            Action: display current solution 

            RENDER.

 

Save solution (ptd particle trace solution file)

Reload solution.

 

Part III:  Define Light/IES Data

Allows the import of photometry data from lighting manufacturers. 

http://www.lightolier.com.

http://www.lighting-inc.com/searchman.html

http://www.hadcolighting.com)

 

IES Data will only work with point lights. 

Show webs:  shows the distribution of light for a given light fixture.

           

Example:

            Download from classes:  iesex/testies.dgn

Use 75rries.ies {Lightolier/12” handing pendent/incandescent.

With two point source lights/ and 0755FR.IES and 0584FR.IES data sets for 12” pendentive and 12”pendentive with aluminum reflector - 150 Watt bulbs.

Load shp file … Do current particle trace solution or make new one.

Adapt to brightness as necessary

See also lamps.html in same directory.

 

 

Part IV:  Overall Concepts

 

Question 1: How do I get a "good" particle Trace solution?

Answer: There are several different ways to achieve better results when we Particle Trace render. Below are a few ways to accomplish this.

 

*           Step 1 - Raytrace

First thing to do is open the rendering tools, and render the scene using Raytrace to see what the scene looks like currently, but be sure to turn off ambient and flashbulb lighting. If the scene does not look good in Raytrace, then chances are they are not going to look good in a Particle Trace solution. It may be too dark, then we need to address the lighting by adding more natural light. If the scene is brighter than desired, then the lights need to lessen by lowering the intensity. So when the scene looks well lit and everything is in clear view.

 

*           Step 2 - Particle setup

Use the default settings first, to see what you get.

1.         1 million particles

2.         Mesh smoothness on 3

3.         Check off "RayTrace Final Display" so we can see the results faster.

 

To speed up the process is to check on "Raytrace Direct illumination" in the Particle Trace setting dialog box. With this setting checked on, the raytracer will compute the shadows from the light source, but not the reflected light.

 

*           Step 3 - Brightness

The first rendering may appear darker than the Previous Raytrace rendering. This can be fixed by adjusting the brightness multiplier.

 

*           Step 4 - AMP (Add More Particles)

Add more particles if:

1.         There is tiling or faceted elements then more particles are needed. Some edges can not be smoothed if the angle is too sharp.

2.         There is color blotches randomly in the scene.

 

Try bumping it up to 5 million particles in the scene, but to do this efficiently, change the Action setting to "Add more particles and redo mesh" and set the particles to 4 million. Since there is already 1 million particles in the scene, adding 4 million more will give an even total of 5 million.

 

It may look better, but it may not look good enough. Adding more particles is the best way to get the scene looking better. If some elements do not smooth out then they probably will never smooth out enough. This is related to how the element was modeled. If the angles of the edges are too sharp it will be able to be smoothed out. It is like trying to smooth out a cube. Thus this is the best it will get.

 

*           Step 5 - Mesh smoothing To change the mesh settings, which will create more detail, first you need to click the Redo Mesh button, since you are not adding particles; you do not need to recalculate the shooting of the particles. Setting the smoothness setting to a lower value such as 1, the rendering, will be less detailed and the particles will spaced further apart, which can produce the colored spots. This is because the mesh is not as detailed and will not except as many particles; hence the colors become blotchy. So the default setting of 3 may be good enough.

 

*           Step 6 - Final touches Once you are satisfied with the detail of the solution you can display the final rendering for the view by going to the Particle Trace settings and selecting "Ray Trace Final Display" then selecting "Redisplay Solution and select the view to render the scene for a final rendering. This will combine the Particle Trace solution with a Raytrace rendering. The Particle Trace solution is not a rendering solution on it own, it is only a lighting solution. Raytracing the scene will display the highlights and reflections of the elements in the scene. Not using "Ray Trace Final display" speed the time for the rendering process. This helps when you are only working on the Particle Tracing solution and not concerned with the display of the highlights and reflections.

 

IES Data: Manufacturers provide this data on spread and intensity of light that can be substituted for lighting setup parameters. Should be used on point source lights only.

Illumincating Engineering Society (formed in 1906) (IESNA/IES) – Included Honory member Thomas Edison.

 

Question 2: What settings values are recommended for the initial rendering?

 

Answer: Using the default settings is a good place to start, they are:

 

*           1 Million Particles

*           Mesh settings/Smoothness of 3

*           Uncheck "Ray Trace Final Display"

*           Turn on "Ray Trace Direct Illumination" in the Raytrace settings

 

Part II: Notes on rendering setup (rendering:general)

 

do for x:/Arch541f03/lec8/test.dgn

 

            shadow maps (see general ... leave off save shadow maps)

 

            anti aliasing grid side (draw pixels and diagonal lines)

                        grid size

                        2 means 4 passes on a 2x2 grid

                        3 means 9 passes on a 9x9 grid

 

            stroke tolerance - maximum deviation of curve geometry from

            true pixel locations where all curves represented as polygons

            how many edges in polygon

 

            shadow tolerance - how close shadows are to cast shadows

            prevents from objects casting shadows on themselves,

            higher values means lower accuracy

           

            shadow filter size - softness of shadows , higher value means

            softter shadow (describes number of pixels to look at in the

            shadow map) ... too large means no shadows, too small means

            objects cast shadows that conceal themselves.