Rendering Approximation Panel Quick Help

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Mesh Generation Options
This dialog controls how the mesh is created for the rendering process.  The default is now to utilize the Viewport Mesh which already exists if you are using the "Smooth & Highlights" or one of the other shaded display techniques.  This is the fastest option because the mesh already exists but it may not produce the best quality results.  To get the highest quality rendering with an optimal number of polygons, you should utilize the "View Dependent Approx" mesh generation with "Production" settings.

NOTE: To change the Rendering Approximation settings of many NURBS Brep Objects at one time, select them and use the "Pwr_NURBS" command.

View Dependent Approx:  Mesh quality will adjust depending on how large the object is in the view.  A sphere which covers 10 pixels on the screen will get a lot fewer polygons than a sphere which covers 100 pixels.  The view will maintain the same display accuracy.  The "Face Chord", "Edge Chord" and "Max Edge" will be defined in terms of the number of pixels.  For example if you wanted the maximum deviation from the precise surface to be 1/2 of a pixel you would set the Face Chord to 0.5 with the "View Dependent Approx" set.  This option could also be called intelligent mesh generation because it will regenerate the mesh to maintain a consistent display quality.
Size Dependent Approx:  Will generate the same number of polygons each time.  The number of polygons is dependent on the size of the object (not how big the object looks in the view).

Render Viewport Mesh:
  Rendering will use the same mesh that the display / viewport uses.  Thus, the rendering quality will be identical with the display quality in the viewport.  You can adjust the viewport display settings dialog to change the quality of this display.  NOTE: The display quality settings on this dialog have no effect when using the viewport mesh.

  Rendering Parameters  

The Rendering Parameters describe constraints to be used during the process of creating a mesh from the precise smoothed surfaces. 

Face Approx Angle:  Defines the maximum angle for a polygon face.  Faces with an angle greater than this value will be sub-divided into multiple polygons.  Decreasing this value will increase the quality of the image.  A face approximation angle of 10 degrees will produce at least 18 divisions from the top to the bottom of a sphere and at least 36 division around the equator for a total of at least 1296 triangles. 
Edge Approx Angle:  Similar to the "Face Approx Angle", but defines the maximum angle for a polygon edge.  By default (when this value is set to zero), it will use the same value as "Face Approx Angle". 
Face Chord %/Pixels:  Chord height is defined as the maximum absolute error between the mesh and the actual precise geometry. The percentage is based on the size of the object when using "Size Dependent Approx" and the number of pixels on the screen when using "View Dependent Approx". Adjusting the Chord Height of the Face is the preferable way to increase the mesh quality without getting too many polygons. 
Edge Chord %/Pixels:  Similar to the "Face Chord %/Pixels", but defines the maximum angle for a polygon edge.  By default (when this value is set to zero), it will use the same value as "Face Chord %/Pixels".   
Max Edge %/Pixels:  Sets the maximum length for any mesh edge.  This value will be in percentage of the object size if using "Size Dependent Approx" and in number of pixels if using "View Dependent Approx".  In general you should not go below 2% of the size or below 10 pixels because it will produce too many polygons. 

  Mesh Quality Presets  

To make your life easier, we have defined 3 settings that automatically change the Rendering Parameters.  The default "Production" should give you an extremely high quality image without polygonal artifacts most of the time.  Occasionally you may have to do further adjustments.

Draft:  Lowest quality mesh generation setting.  This option will generate the fewest polygons.
Good:  Medium quality mesh generation
Production:  Highest quality mesh generation setting.  This option will generate the largest number of polygons.

  Misc. Options  

Weld and Smooth:  Smooths out the mesh, removing small edges and polygons.  Use this option when you convert to editable mesh or poly.
Save Render Mesh:  Saves render mesh to disk for faster rendering of models when you re-open them.