RobUSMC

Raytrace Speed

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In general the larger processors are going to be faster even though they may sometimes report lower frequencies.

For example: A 6-core even running at 1.2GHz would probably still beat out a quad core running at 2.8GHz.

 

This is because it has more bandwidth to process tasks with than the quad core.

 

That being said, it is not quantifiable unfortunately, but there is a definite difference. There are too many variables to consider with every scene, but as an example, The same scene using the same ray trace settings took 4 days on my laptop which was using an intel i5(2-Cores at 2.3GHz) to complete the 500 passes that I set it for. On my desktop using an i7(4-cores at 1.7GHz) it took 24hrs.

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....but as an example, The same scene using the same ray trace settings took 4 days on my laptop which was using an intel i5(2-Cores at 2.3GHz) to complete the 500 passes that I set it for. On my desktop using an i7(4-cores at 1.7GHz) it took 24hrs.

 

Wow! I am such a lightweight. 4 days and 500 passes?

How hot was the laptop after that stint? :o

 

Maybe it's my short attention span but I never let them

run anywhere near that long. With Ray Traces it seems

that I am constantly fighting the laws of diminishing returns.

Can you still discern changes in the image quality after so

many passes?  

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Spot on Rich. The law of diminishing returns applies to Raytracing. Each pass imparts a refinement based upon the previous pass. If one assumes that this refinement provides a 50% improvement then the following can be assumed.

 

1 pass = 50% of the maximum image quality

2 passes = 75%

3 passes = 87.5%

4 passes = 93.75%

5 passes = 96.875%

 

After 10 passes if the image quality from a resolution perspective is unsatisfactory then an approach other than increasing the number of passes should be considered. The best I have found is to increase the pixel count. For example, if the original image size in pixels is 1960 X 1080 then increase this to 3920 X 2160, this will quadropal the number of pixels used to render the scene. I ran a 1960 X 1080 scence for 50 passes which took about 1 hour, the same scene at 3920 X 2160 was run for 10 passes which took only 30 minutes and the resolution was siginificantly better than the first. Like a digital camera, the more pixels the better the resolution. A 1960 X 1080 scene is equivalent to a 2 mega pixel camera.

 

Just a note when using the Raytrace DBX to increase the resolution. If the width & height is set in pixel units then the DPI setting has no impact on the reolution, it only determines the intended printout size. However, if the width & height is set in inch units then the DPI setting determines resolution.

 

Graham

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"Just a note when using the Raytrace DBX to increase the resolution. If the width & height is set in pixel units then the DPI setting has no impact on the resolution, it only determines the intended printout size. However, if the width & height is set in inch units then the DPI setting determines resolution"

 

That is a very important point!  Thanks for posting that.

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This Raytrace took over 50 min. and had only done 6 passes.  I would agree with Kirk that if I had saved the drawing and only took a Raytrace of the area I wanted it would have been much faster.  That being said it is a waste of time either way.  I feel like I have a graphics card that should make lightspeed of this but I now feel that I need a new graphics card to keep up.

 

Just from your image, those couches look like they will be very high in face count - in those button details.

 

And - as Kirk pointed out, would you really have all those can lights on in an interior view?  

 

So - very high face count on each of several sofas and chairs + multiple light sources, each calculating each of those faces - logarithmically increases ray trace time.  Simplify!

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The following demonstrates the impact on Raytrace time in comparison to light type setting, surfaces, photon mapping and caustics.
 
The base scene - single room, 1 object (9510 surfaces), 8 mini can lights
The base Raytrace settings - use camera view settings, Uniform intensity 5.0, Photon & Caustics Off
 
10 Passes used in all sample runs. i5 2540M quad core, 2.6 GHz. 1200 X 571 pixel size.
 
                                                                                      Spot      Point
 
Lights off, 9,510 surfaces                                              1:01        1:01
Lights on, 9,510 surfaces                                              1:09      14:05
Lights on, 114,200 surfaces                                          1:15      16:55
Lights on, 114,200 surfaces, Photon "On"                     3:37     19:27
Lights on, 114,200 surfaces, Photon/Caustics "On"      3:42      20:17
 

This demonstrates that "Point" lights have the greatest impact on Raytrace time. It also shows that the number of surfaces are of minor consequence.
 
If your Raytrace times are unacceptable to you then the things to do are:
 
1.) Change point lights to spot lights.
2.) Turn off all lights in your plan not associated with the scene.
3.) Turn off Photon mapping when spot lights are used.
 
If your scene lacks sharpness then the only way to improve this is:
 
1.) Increase the width & height in pixels and,
2.) Post process the image in an image editor.
 
Always keep in mind that after about 10 passes you have likely attained 90% of the potential quality that can be achieved for any given scene. Running 100's of passes will not significantly improve things.
 
If these techniques are unacceptable then your only option is to throw more processing power at it. Currently Raytracing is 100% CPU dependant so your main processor is the key, your graphics card has nothing to do with it. If your system is several generations old then one of the top consumer grade i7's will easily reduce your times by at least 50% or more. Beyond that you will need to move to Zeon grade processors most likely in a dual configuration.
 
Graham
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Larry has dual Zeon's, it would be interesting to see the difference.

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Here is a comparison that demonstrates the impact with Intel's latest Skylake i7 6700K processor.

 

10 Passes used in all sample runs. 1200 X 571 pixel size.

 

 

                                                                                    I5 2540M 2.6 GHz              i7 6700K 4.0 GHz

 

                                                                                      Spot      Point                       Spot     Point

 

Lights off, 9,510 surfaces                                              1:01        1:01                        0:17     0:17
Lights on, 9,510 surfaces                                              1:09      14:05                        0:20     3:54
Lights on, 114,200 surfaces                                          1:15      16:55                        0:21     4:55
Lights on, 114,200 surfaces, Photon "On"                     3:37     19:27                        1:03     5:45
Lights on, 114,200 surfaces, Photon/Caustics "On"      3:42      20:17                       1:09     5:48

 

This new processor is between 3 to 4 times faster depending upon the task. Another noticeable benefit is that it handles multi-tasking really well when Raytracing with all cores assigned and running flat-out. The i5 is a T240s ThinkPad that cost about $2,300 three years ago, the i7 is a new Alienware X51 R3 costing only $1,600.

 

Graham

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Graham 

That is great info! thank you for taking the time to compile the data!

 

cheers,

Michael

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Thanks everyone for the support.
 
The issue concerning Raytrace times appears to be an ongoing issue for many users, especially to those who are new to Chief. I am certain that Raytracing for many, including myself, is an extremly important tool that facilitates our ability to express our ideas and thoughts in a format more conducive to our clients capacity to envision their projects in a realistic 3 dimensional perspective. For me this is a great way to differentiate myself from many competitors who only rely on plan and elevations.
 
Given the above, it can be a bit of a double edged sword, especially if the time to run a Raytrace is ridiculously time consuming. For example, a typical kitchen layout will include between 4 - 6 Raytrace views. If each view takes 1hr then a minimum of 4-6hrs is required and this assumes that I do not notice something amiss, which will require a rerun. To make matters worse it's inevitable that upon review the client will request some changes. Even a simple 5 minute fridge change now requires those Raytrace views to be update, another 4-6hrs. As we all have experienced these change request can be numerous and the Raytrace time continues to add up. I can recall many projects were this time exceeds the actual base design time, not very effective use of my time. It can also impede my ability to resond to requests in a timely manner.
 
Hopefully the examples provided in my previous two posts will help users to improve their Raytrace throughput and also gain an improved perspetive when considering a hardware upgrade/purchase driven by this parameter.
 
Many Thanks,
Graham
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Fantastic thread guys. I have learned more in these last few minutes reading through this than in the hours of video tutorials :) 

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I would try adjust (increase) the emissive property of the color/ texture on the ceiling.

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I have been concentrating on renders this last couple of weeks and its been a steep learning curve even with all the great advice here. Every room seems to have its own unique characteristics ( at least mine do ) and i have not found a "rule" that applies to all. Both Dennis and Micheal offer sound advise but also try playing with natural sunlight as you have  a large window in the shot. It takes a bit of messing around to get the sun angle just right but it really added a level of realism to some of my renders that I didn't think possible. The attached image is one of my early attempts :)

post-2914-0-19958900-1451251607_thumb.jpg

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Warren,

 

   As you are seeing ray tracing is an art form not just "flipping switches".  i.e. lights on and off.

Sometimes I use photon mapping, sometimes not.  Closed rooms (no windows) require

different settings than rooms with sun light.  IF you don't use photon mapping than you will probably

need to up the interior ambient light for a ray trace. Problem there is it looks TOO bright for standard

renders.  Material settings also play havoc.  You have to be careful of materials set to "polished" as

they tend to blur the light especially on floors.  I prefer to use reflective.  Occasionally I will use polished

on dark color furniture.  It really is a bit of trial and error.  But the good news is you are getting better!

Keep up the good work.

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Wow Warren...this is looking good.

 

I'm jealous!

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Thanks guys. Im really trying to maximize the ray trace function of CA to its fullest. I can't justify ( for now ) investing another $2000 odd for a program like Lumion. Does the level of 'realism' it offer really aid the sale of your product as much? Will the regular client even notice a difference? Your feedback and experience will be appreciated as always. 

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I use Thea, and I don't know if I would say it help sell more, but they definitely notice a difference.

 

I did a few renders for a contractor of ours, and shortly after I was approached by another one asking why we don't do those really high quality pictures for them too!

 

So...needless to say it gets noticed.

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I don't know about the practical side of things but as a tech support analyst, I get a lot of calls and questions about how to make a rendering look better for both home designer and chief users.

So it is a hot topic and I would imagine that clients are asking for this or designers are trying up their game and provide better eye candy for their clients.

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My four and a half year old Dell desktop has an Intel i7-2600 CPU @ 3.40 Ghz.  Makes wonder how it wood compare to the newer Intel i7-4790K CPU @ 4.0Ghz, in terms of renderings.  Both are four core processors.  If I was to ever build myself a dedicated CADD / work computer, I would probably consider the 4790K.  However, I have often wondered what role more processor cores play in terms of speed and time it takes to generate renderings,

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