V-Ray Illumination Relevance Test

This page offers a comparison test case of V-Ray results to officially conducted research on illumination validity of other renderers.

Overview

This test case recreates the daylight simulation setup from a paper called Experimental Validation of Autodesk® 3ds Max® Design 2009 and Daysim 3.0 (Reinhart, 2009) using V-Ray Next for Autodesk 3ds Max 2017.

The referred experiment conducted by Reinhart "compares the daylight simulation results with Autodesk® 3ds Max® Design 2009 software (3ds Max Design)... to real indoor illuminance measurements in a sidelit space"¹. The goal we set with this test case is to compare how the advanced technology of V-Ray Next performs with the input of Autodesk's initial research. Further, we explore how to provide faster and accurate renderer with better render image quality using Reinhart's results as a benchmark.

Prerequisites

As our starting point is the referenced paper, we should firstly outline several important things in relation to it.

The software used is Autodesk's 3ds Max Design 2009. V-Ray Next does not support 3ds Max versions prior to version 2013. That necessitated the use of an updated 3ds Max version for the test. We used the 3ds Max version 2017, as Mental Ray is still integrated and shipped within the official version. That allows for later comparison, if needed. In regards to the provided features, 3ds Max fully covers 3ds Max Design ones.

Preparation of the 3D model and scene

The test scene in this comparison case was recreated as close as possible to the referenced paper. The 3d model was rebuilt using all available data for the research. Missing detailed measurements for the window frames and wall thickness were adjusted to match the original model as there were no measurements provided for them in the research paper.

There is one thing intentionally altered in the scene - the unsupported Daylight system setup. Instead, the complete system was replaced with a single VRayLight, type Dome. Its texture was set to Physical Sun & Sky Environment map being calculated with the exact same weather file placed in a Sun Positioner helper. This setup translates successfully the Perez Sky model, originally used as Daylight sky in 3ds Max Design, into a map that is renderable in V-Ray Next. The Dome texture resolution was increased to its maximum (8192) for most accurate sampling of the texture. Since V-Ray Next is optimized to calculate light from Dome lights without the need of Light portals, there were none created and used in our scene.

Picture of the east room of the NRC Daylighting Laboratory where the original physical measurements took place
Original Image found in Experimental Validation of Autodesk® 3ds Max® Design 2009 and Daysim 3.0 (Reinhart, 2009)

Model recreation with V-Ray Next in 3Ds Max 2017 accentuated with VRayDirt and VRayToon

Scene recreation with V-Ray Next in 3Ds Max 2017. Note that the original photo documents a cloudy day while the measurements are executed on a sunny one, hence the sharp shadows in the rendered image.

Preparation of the materials

V-Ray materials were assigned with the same parameter values as in the paper. Only the refraction value of the glass material needed custom adjustment. The window panels in our scene were created with separate objects for each glass pane. Hence, applying the value registered for an Arch and Design material of a double glazing window (meant for simulating the two panels out of a single object) to these two separate objects with a V-Ray material, would have been incorrect. Instead, the measured transmissivity of 72.0% from the NRC Daylighting Laboratory research was applied.

In order to determine the correct refraction value, the window was placed in another empty scene with white background and refraction environment, and black GI environment and reflection environment. The target was to measure 72% gray as rendered result, which represents the transmission from refraction in an exclusive manner. A value of 72% gray is represented as 183.3 of [0-255] RGB value range or 0.72 of its floating-point number representation. The refraction color value of 237.2 produced the closest result (183 8-bit color value and 0.719 floating-point number color value to be exact).

The complete materials list is provided as table below. It should be noted that for all parameters not mentioned in the V-Ray materials, we keep their default values. The exact floating-point number color values were put with Maxscript in a VRayColor map to avoid the value being rounded to integer when processed with the UI (Example: $Walls.material.materialList[3].texmap_diffuse.color = color 224.756 224.756 224.756).

Items	Daysim / Radiance materials	3ds Max Design / Arch & Design materials	3ds Max / V-Ray Next materials
InteriorBackWall	void plastic InteriorBackWall 0 0 5 0.77 0.77 0.77 0.004 0	#diff_color (color 197 197 197) #refl_weight 0.004 #refl_func_low 1.0 #refl_func_high 1.0	Diffuse VRayColor 197 197 197 Reflect VRayColor white, rgb multiplier 0.004 Fresnel reflections disabled
InteriorCeiling	void plastic InteriorCeiling 0 0 5 0.88 0.88 0.88 0.001 0	#diff_color (color 224.765 224.765 224.765) #refl_weight 0.001 #refl_func_low 1.0 #refl_func_high 1.0	Diffuse VRayColor 224.756 224.756 224.756 Reflect VRayColor white, rgb multiplier 0.001 Fresnel reflections disabled
InteriorFloor	void plastic InteriorFloor 0 0 5 0.12 0.12 0.12 0 0	#diff_color (color 30.49 30.49 30.49) #refl_weight 0.0	Diffuse VRayColor 30.49 30.49 30.49 Reflect VRayColor white, rbg multiplier 0.000
InteriorFrontWall	void plastic InteriorFrontWall 0 0 5 0.75 0.75 0.75 0.006 0	#diff_color (color 192.255 192.255 192.255) #refl_weight 0.006 #refl_func_low 1.0 #refl_func_high 1.0	Diffuse color VRayColor 192.255 192.255 192.255 Reflect color VRayColor white, rgb multiplier 0.006 Fresnel reflections disabled
InteriorSideWall	void plastic InteriorSideWall 0 0 5 0.38 0.38 0.38 0.004 0	#diff_color (color 192.255 192.255 192.255) #refl_weight 0.004 #refl_func_low 1.0 #refl_func_high 1.0	Diffuse color VRayColor 192.255 192.255 192.255 Reflect color VRayColor white, rgb multiplier 0.004 Fresnel reflections disabled
MoullionMetalSilver	void plastic MoullionMetalSilver 0 0 5 0.62 0.62 0.62 0.07 0	#diff_color (color 170.745 170.745 170.745) #refl_weight 0.004 #refl_func_low 1.0 #refl_func_high 1.0	Diffuse color VRayColor 170.745 170.745 170.745 Reflect color VRayColor white, rgb multiplier 0.004 Fresnel reflections disabled
ExteriorParkingLot	void plastic ExteriorParkingLot 0 0	#diff_color (color 28 28 28) #refl_weight 0.0	Diffuse VRayColor 28 28 28 Reflection VRayColor white, rgb multiplier 0.000
ExteriorGravelNearFacade	void plastic ExteriorGravelNearFacade 0 0 5 0 0 0 0 0	#diff_color (color 0 0 0) #refl_weight 0.006	Diffuse VRayColor 0 0 0 Reflection VRayColor white, rgb multiplier 0.006
ExteriorWall	void plastic ExteriorWall 0 0 5 0.58 0.58 0.58 0 0	#diff_color (color 192.255 192.255 192.255) #refl_weight 0.006 #refl_func_low 1.0 #refl_func_high 1.0	Diffuse color VRayColor 192.255 192.255 192.255 Reflect color VRayColor white, rgb multiplier 0.006 Fresnel reflections disabled
ExteriorBlackCloth	void plastic ExteriorBlackCloth 0 0 5 0 0 0 0 0	#diff_color (color 0 0 0) #refl_weight 0.006	Diffuse VRayColor 0 0 0 Reflect VRayColor white, rgb multiplier 0.000
DoubleClearGalzing	void glass DoubleClearGalzing 0 0 3 0.72 0.72 0.72	#diff_color (color 0 0 0) #refl_color (color 255 255 255) #refl_gloss 1.0 #refl_weight 1.0 #refr_color (color 207 207 207) #refr_gloss 1.0 #refr_ior 1.5 #refr_weight 1.0 #refl_func_fresnel false #refl_func_low 0.0 #refl_func_high 1.0 #refl_func_curve 4.816 #opts_1sided true #opts_do_refractive_caustics false #opts_skip_inside true #opts_backface_cull false	Diffuse color VRayColor 0 0 0 Reflect color VRayColor 255 255 255 Refract color VRayColor 237.2 237.2 237.2 Refract IOR 1.5
ExternalWindowSill	void plastic ExternalWindowSill 0 0 5 0.60 0.60 0.60 0.15 0	#diff_color (color 178.49 178.49 178.49) #refl_weight 0.15 #refl_func_low 1.0 #refl_func_high 1.0	Diffuse color VRayColor 178.49 178.49 178.49 Reflect color VRayColor white, rgb multiplier 0.15 Fresnel reflections disabled

Measuring the Light Values

The test scene holds a full 24-hour daylight animation. The sun position in the Physical Sun & Sky environment Dome light is controlled with a Sun Positioner helper, set to follow the Daylight animation for the same date as the Sunny day research - 13^th of May 2007. Each frame in the test scene corresponds to 5 minutes offset. A custom script was executed to automate light values calculation at each frame of interest, where illumination curve was provided in the paper. The calculation itself was handled by VRayLightMeter. The V-Ray Light Meter is a utility that provides exact light measurement values at distinct points in the scene where its gizmo is located.

Results

The VRayLightMeter provides several points of measurement at once. Once calculated, the result for the current frame is automatically saved to a .csv file with all of the final illumination values. Only the result from the VRayLightMeter's central point, numbered 4^th in the .csv files, under Total lighting, was used in our test. It is the most accurate having in mind the small surface on the DS sensors.

Outside sensor on Sunny Day (May 13^th) graph from the original research presents the data for the hours from 4 AM to 8 PM. VRayLightMeter was calculated in frames from #48 to #240 and saved to .csv files for each frame. The VRayLightMeter result (in orange) is laid upon the original graph data in the picture below.

This graph is available in the provided .ods file.

In a similar manner, the VRayLightMeter result for the indoors DS2 sensor was calculated and saved in .csv files for each frame between #48 and #192 (total of 145 files) for the same Sunny day (May 13^th).

The TC1 Base case measurement from DS2 sensor is overlaid with the results from VRayLightMeter (in orange) in the graph below.

This graph is available in the provided .ods file.

It must be noted that the exact positions of the high and low points correspond to the exact moments when the inside sensor is directly lit by the sun or falls in the window frame shadow. Since we used the model from the original paper as reference, those transition moments match perfectly in time. The Radiance (Daysim 3.0) data for the inside sensor produces a graph that is far from the expectations but accurately represents the data in the provided research files.

Both graphs were stripped off their result data for the frames #48-55 and #232-240. These frames correspond to early morning (4:00-4:35) and evening (19:20-20:00) times. The reason is that at these frames the sun is positioned below the horizon and so the weather data file provides 0-s as an input information. 3ds Max's Physical Sun and Sky Environment map integrated behavior automatically switches the sky model to another in such cases, which results in distorted output. These frames are considered to return minimum light values.

Project Files

Conclusion

We believe these test results are promising and provide a good starting point for further experimental inquiries.

It must be noted that V-Ray Next uses an improved algorithm for VRayLightMeter calculations, which enabled the proper execution of the test. The output with V-Ray 3.6 and earlier versions would differ regarding the inside sensor, because pure Brute Force calculations with limited sampling are used and issues would sometimes occur with GI rays going through glass objects.

Reference

1 - Christoph Reinhart, Experimental Validation of Autodesk® 3ds Max® Design 2009 and Daysim 3.0, Autodesk Canada Co. Media & Entertainment, 2009

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