The rendering techniques provided by StrataStudio are very good and suitable for many applications but the realism possible is quite limited. Radiance is another rendering program, it is free (public domain) and has big advantages for architectural rendering. Most of these advantages are a consequence of its radiosity/raytracing approach which uses a much better lighting model than the conventional raytracing offered by StrataStudio, this is especially so for interior scenes. Radiance also has the capability of doing quantitative lighting analysis including daylighting analysis.

In order to use Radiance with the StrataStudio package we have written a translator that takes a DXF file as output from StrataStudio and creates a Radiance scene description file ready for the Radiance rendering package. The program is called strata2rad and runs on the Universities main UNIX machines located in the Computer Centre (although the local personal computers in the School of Architecture act as terminals to these UNIX machines over the campus ethernet network). The program has one required argument which is the DXF file exported from StrataStudio, it writes the Radiance scene description (header, lighting, materials, and geometry) to STDOUT, this would normally be piped to a file or to some other process in the normal UNIX manner. There are three switches which will determine what data is exported, they are l (light sources), m (materials), and g (geometry). Thus the most common method of calling the translator from UNIX would be

   strata2rad -l -m -g mydxffilename > myradiancefilename

This would output lights, materials, and geometry. If the model was later modified in StrataStudio then the next time it was converted only the geometry may need to be created, this would be done with

   strata2rad -g mydxffilename > myradiancefilename

A major design aim for the translator was that this file can be rendered without modification and thus a relatively novice Radiance user can easily get good initial results.

The Radiance scene description file created by this translator contains the following major sections

• a header including the bounding box of the model
  
• some default light sources including two distant light sources (sun and moon) and the template for other lights.
  
• a list of material definitions
  
• the geometry making up the scene and modified by the appropriate materials. StrataStudio exports only polygons to its DXF output files thus "polygon" is the only Radiance geometric primitive created.

The StrataStudio part names are used as the Radiance material names except that all white characters (spaces, commas, etc) and stripped out to ensure a legal Radiance material name. This material name conversion is of vital importance, it allows the user to later modify the material descriptions without editing the geometry. Note that if parts were not initially used when creating a model it is a simple matter to select pieces of the model and turn them into named parts. Any geometry which is not a part will have a material corresponding to the StrataStudio file name.

Keywords in the StrataStudio part name are used to specify material types for Radiance. The translator will attempt to create an appropriate material type by looking for Radiance material type keywords within the StrataStudio part name. For example, the StrataStudio part name "green glass table top" will have a Radiance material type "glass", "mirror plate" will become a "mirror" material type. The translator knows about the following material type keywords.

    metal        illum         dielectric
    glass        light         trans
    plastic      glow          mirror
                 spotlight     interface

If the following keywords are found within the ArchiCAD material name the Radiance material type will be "metal". So for example the part name "copper panel" will have a Radiance "metal" material.

    iron         copper        steel
    brass        bronze        gold
    platinum     lead          aluminium
    titanium     silver        zinc

All unrecognised material types will be defined as a Radiance "plastic" material.

The translator know about the following colours, if these keywords are not included in the part name, a 50% grey is used.

    red          green         blue
    cyan         magenta       yellow
    black        white         grey
    brick        pink          maroon
    brown        orange        gold
    turquoise    indigo        purple        violet

The translator will set some of the other material parameters automatically. Also various keywords will affect the specular and roughness characteristics of "metals", "plastics" and "trans" material types. These keywords are

    dull         shiny
    matte        glossy
    smooth       rough

The first four affect the specularity, the last two affect the roughness of the appropriate materials. So, for example, if one creates a material in StrataStudio called "shiny aluminium" or "iron, dull smooth" then sensible initial material types and characteristics will be created for the Radiance material description. Of course these would only be very approximate settings and the user would be expected to modify the exact material description for final renderings.

Note that materials could include the material type keywords "light", "illum" or "spotlight" and would therefore become the appropriate light sources for Radiance. For spotlights the user will need to specify the direction vector, by default it is pointing down (0,0,-1).

StrataStudio only uses the 3DFACE primitive in its DXF file export. Most of these polygons will have three vertices although 4 vertex polygons will be created if the vertices are coplanar. The part name is available as the material because StrataStudio puts the part name as the layer control code (8) in its DXF export.

StrataStudio is the upgrade product to StrataVision. The StrataVision product was not suitable for translation to Radiance because it did not export the part names. StrataVision models may be converted into Radiance models by first importing them into StrataStudio.

All restrictions arise from the small amount of data exported to DXF via StrataStudio. Ideally one would like the material names not the part names to be exported in which case the Radiance material names might correspond to the StrataStudio material names.

This translator assumes that the model in StrataStudio has been created using metric units. This is a restriction which arises from StrataStudio's conversion (bug) of all units into inches when exporting to DXF.

The following model was created in StrataStudio as an example of the translation process. StrataStudio is capable of much better rendering but it was not shown here because only the bare geometry is translated into Radiance.

The following image is the rendering of the above after translating the model through the Strata2Rad program. This is the result directly from the translator except for the approximate matching of the camera position and view direction.

This rendering just uses the default material definitions, improvements to the rendering can now be made by designing the material definitions and lighting characteristics. The material list created directly from the translator for the above model follows, it shows the automatic generation of material types, names, and parameters.

void metal matte_lead_slab
0
0
5       0.5 0.5 0.5
        0.8 0.05

void metal iron_roof
0
0
5       0.5 0.5 0.5
        0.9 0.05

void plastic rough_grey_column
0
0
5       0.75 0.75 0.75
        0.05 0.1

void plastic shiny_brown_bondbeam
0
0
5       0.5 0.16 0.16
        0.1 0.05

void plastic shiny_brown_beam
0
0
5       0.5 0.16 0.16
        0.1 0.05

void plastic shiny_brown_cornice
0
0
5       0.5 0.16 0.16
        0.1 0.05

The following shows the structure of a Radiance scene file generated by the translator.

# --------------------------------------------------------------
# Strata2rad output (From StrataStudio to Radiance converter)
# --------------------------------------------------------------
# The model bounds
#  -55.5729 < x < 114.838
#  -114.786 < y < 55.6241
#  -19.8846 < z < 97.8431
# --------------------------------------------------------------
# An example sky
void glow dim
0
0
4 0.35 0.4 0.55 0
dim source sky
0
0
4 0 0 1 360
# --------------------------------------------------------------
# An example sun
void light solar
0
0
3 800 800 800
solar source sun
0
0
4 0 0 1 5
# --------------------------------------------------------------
# An example moon
void light lunar
0
0
3 200 200 200
lunar source moon
0
0
4 1 1 1 5
# --------------------------------------------------------------
# An example light source
#void illum lighting
#0
#0
#3 1000 1000 1000
#lighting sphere bulb
#0
#0
#4 x y z 0.03
# --------------------------------------------------------------
# Material definitions (8 of them)

The materials would normally appear here

# --------------------------------------------------------------
# The Geometry

The geometry would normally appear here

# --------------------------------------------------------------
# The end

Infini-D

This translator, while initially designed to support a minimum of the DXF specification from StrataStudio, has been successfully applied to the DXF files from Infini-D. The example on the right is courtesy of Rob Fitzsimmons. Some hints for use with Infini-D are as follows: The Infini-D coordinate system is different from StrataStudio, this can be fixed by rotating the object by -90 degrees about the x axis in Infini-D or Radiance. As with StrataStudio, since the materials for Radiance are determined from the object name, objects should be named accordingly. Convert extrusions to meshes before exporting, may help solve non planar polygon errors in Radiance.

Description

"Upfront -> Radiance" translator provides a means of converting Alias Upfront models into a scene description format suitable for the Radiance rendering package.

To use this translator

• open the model in Alias Upfront
  
• export to another file as Architrion3-text
  
• run this translator and open the Architrion text file
  

The Radiance scene description file will have the same name as the exported Architrion text file with the extension ".rad". Note: this is not a general Architrion translator, it only copes with the block entities created by Alias Upfront.

The resulting Radiance scene description will have the same coordinate system as the original Upfront model. The file will contain:

• a header (which includes the model bounds)
  
• a few light sources at the bounds of the model
  
• a material for each layer/colour combination used in the model
  
• the geometry of the scene.
  

Restrictions

• Colours are only maintained for individual objects. The colour of single faces of an extruded polygon will be lost unless the face is made as a separate object.
  
• The only primitives used by Upfront are polygons, this means that objects such as spheres will be made up out of many polygons and perhaps should be created separately in Radiance as sphere primitives.
• Only version 1.02a of Alias Upfront and later has the Architrion3-text export option.