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Rhino

Converting IGES Files

Rhino will read IGES files of solid or surface based models and convert them to NURBS surface based models. The NURBS surfaces can then be easily converted to polygon meshed based models for use in Photopia, but before they are converted make sure that the parts in the model that use different material finishes are separated onto different layers. This is important since materials are assigned by CAD layer inside Photopia and sometimes all parts are put onto a single layer in IGES files. In this case, you must define a new layer for each part with a different surface finish and then move the parts to their appropriate layer. The steps for this are listed below:

  1. Define all of the new layers you will require by selecting Edit -> Layers -> Edit Layers. from the main menu.
  2. Click the New button with the Edit Layers dialog.
  3. Type in a name that will help you identify the part. We suggest you use the Photopia layer naming convention to make importing the model into Photopia quicker. The Photopia convention specifies that layers begin with either "REFL-," "TRAN-," or "REFR-" to denote them being for reflectors, transmissive surfaces or refractors, respectively. See Chapter 4 in the User's Guide for more details.
  4. Give the new layer a unique color by clicking on the color patch for that layer.
  5. To help ease the process of assigning the NURBS surfaces to their appropriate layer, we recommend you turn Off each new layer.
  6. Once all required layers have been defined, then click OK on the Edit Layers dialog.
  7. To change the layer of a particular surface, click on one of the boundary lines of that surface. If the boundary you select is shared by 2 surfaces, then Rhino will pop-up a dialog that allows you to toggle or scroll through the alternatives while it highlights them in the CAD view. Pick the surface you desire within this pop-up dialog.
  8. Once the proper surface has been selected, then choose Edit -> Layers -> Change Object Layer from the main menu and select the layer you want from the dialog displayed.
  9. If you turned all of the newly created layers off, then the surfaces will be removed from the display as you assign them to their layers. To finish writing out the DXF file see the FAQ on converting NURBS based surface models to polygon meshed based models.

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Converting NURBS to Meshes

Rhino contains some very good facilities for creating meshed surface models (or polygon based surface models) from NURBS surfaces or solids. NURBS surfaces can be converted to meshes upon exporting them to DXF files or from within Rhino before the DXF export is started. The easiest method is to convert them at the time the DXF file is written. For greater flexibility on the detail of the mesh however, you can create the meshes for each NURBS surface from within Rhino prior to exporting the DXF file.

Converting NURBS Surfaces Upon Exporting to the DXF file:

  1. To convert NURBS surfaces to meshes upon exporting to the DXF file, first select the entire model you wish to export. If the model includes Photopia lamps, then be sure to select from the Top view.
  2. Select File -> Export Selected from the main menu.
  3. Change the "Files of type" filter at the bottom of the dialog to "AutoCAD DXF," navigate to the proper folder, enter the filename and click the Save button.
  4. Rhino will then display the AutoCAD Export Options dialog. You can accept the defaults.
  5. From the Polygon Mesh Options dialog. Select the Detailed Controls. button. Skip to the Polygon Mesh Detailed Options section below.

Converting NURBS Surfaces Within the Drawing Editor:

  1. To convert NURBS surfaces to a mesh based surface from within the Rhino drawing editor, click on the NURBS surface from which you wish to make a mesh.
  2. From the Rhino main menu, select Tools -> Polygon Mesh -> From NURBS Object.
  3. From the Polygon Mesh Options dialog. Select the Detailed Controls. button. Now skip to the Polygon Mesh Detailed Options section below. When finished with that section, return to the next step in this section.
  4. Once the meshed surfaces are created, you can export them to a DXF file by following the steps listed in the first section. Note that we recommend you put all of the meshes onto unique layers to keep them separate from the original NURBS surfaces. When you create a mesh the NURBS surface still exists and unless you separate the 2 types of surfaces onto different layers they will simply be drawn on top of each other. It is important to separate the 2 when exporting to a DXF file since you need to select the particular surfaces you want to export to DXF. If you select both the mesh and the NURBS surface then you will get twice the number of surfaces you expected in Photopia.

Polygon Mesh Detailed Options:

  1. Set the "Max Angle" and "Max Aspect Ratio" according to the detailed required for the particular part. We recommend a "Max Aspect Ratio" setting of 100. This is a setting which dictates how long and thin a triangle can become, the aspect ratio referring to the length of the triangle compared to its width. When set to lower levels, a mesh is created which unnecessarily subdivides long flat surfaces which in reality could be described accurately with a single rectangle.
  2. The "Max Angle" setting refers to the maximum angular difference between the surface normals of adjacent surfaces. When using specular surfaces with relatively small light sources this setting should stay relatively small. We recommend a value of 10 degrees or less. If this value becomes too large, then you will see striations in your light pattern indicative of what the pattern would truly look like if the reflector were really faceted to that degree. If you want a quicker analysis knowing that the striations are not real, then you can set this value to 20 or more. Other general aspects in your light pattern will be accurate. It is common to make course models for early design iterations.
  3. When the surfaces are black or have a material which scatters the light more, like white paint, hammertone, semi-specular, etc., then you can tolerate less accurate surface orientations and still get accurate analyses. The same holds true when larger light sources are used, such as those which have coated bulbs. In these cases you can increase the "Max Angle" to 20 or 30 degrees. Utilize the Preview button to see if the degree of accuracy introduces any obvious geometric problems.

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Importing DXF File Into Photopia

  1. Start by selected File -> Import Luminaire CAD File from the main menu in Photopia.
  2. If you use the layer naming convention for Photopia, i.e. REFL-HOUSING, TRAN-LENS, then Photopia will automatically sense the layer types. If you do not use the Photopia layer naming convention, then you need to specify the layer type in the first import screen within Photopia. After all of the layer types have been specified, click Next at the bottom of the dialog.
  3. The Activate Surfaces screen allows you to specify the surface orientations. Conveniently, the meshes that Rhino makes are such that all polygons of the mesh are oriented the same. Check to see that Photopia has rendered the reflective side of the surfaces in the same color as the layer in Rhino. Note that this is the color that is used on the part when viewed in wireframe mode. We recommend you orient the surfaces of only one layer at a time by clicking on the layer of interest in the list shown in the upper left hand part of the screen. Remember that you can gain full access to all CAD viewing controls by right clicking your mouse in the CAD view window. If the surfaces on a given layer are not rendered in the appropriate color on their reflective or "front" side, then select the "Reverse" Surface Orientation method, then click the "Select All Surfaces" button, then click the "Apply" button. This switches the orientation of all surfaces on the given layer. Once all surfaces have been properly oriented, click Next.
  4. The last step is to add the lamp(s) to your model. Select the lamp you require from the list within Photopia and use the controls provided to add it and place and orient it. If you need more than one lamp, then add more lamps in the same manner. It is sometimes necessary to change the View Style of the CAD view to "wireframe" to see lamps within the luminaire. Click the Finish button when done.
  5. You are then prompted to name and specify the location of the project. The default name and location match that of your CAD file. Note that the Photopia project is comprised of a series of files all sharing the same filename prefix.