Cortona spline technology

The key benefits from the use of spline objects include:

The high quality of a smooth surface can be described using VRML.

It is required less computing resources for achievement of high quality.

The size of the VRML-file decreases essentially (up to 10 times) without degradation of surface quality.

The smooth variation of input parameters results in transformation of the spline surface that is worth to simplify the creation of realistic animations.

The dynamic detailed elaboration provides the balance between necessary quality and frame-rate.

The function of quality allows to operate a degree of detailed elaboration of a surface.

SplineCone

SplineCylinder

SplineElevationGrid

SplineExtrusion

SplineFaceSet

SplineSphere

The method of spline representation of geometry objects is based on three-cubic spline interpolation, which is performed with Cortona VRML client automatically using incoming polygonal data (control vertices). So a spline surface includes all control vertices of the polygonal model. While rendering, a surface is broken down (tessellated) into a set of triangles approximating the spline surface. To balance between quality and the frame-rate, a surface curvature and number of triangles are taken into account. Moreover, it's possible to control the tessellation using the quality function.

ParallelGraphics has also developed the suitable converter for the translation of standard polygonal objects to the spline analogies.

Geometric spline nodes

SplineCone { field SFFloat bottomRadius 1 field SFFloat height 2 field SFBool side TRUE field SFBool bottom TRUE field MFFloat distance 10 field MFFloat quality [0, 0.75] }

SplineCylinder { field SFBool bottom TRUE field SFFloat height 2 field SFFloat radius 1 field SFBool side TRUE field SFBool top TRUE exposedField MFFloat distance 10 exposedField MFFloat quality [0, 0.75] }

SplineElevationGrid { eventIn MFFloat set_height exposedField SFNode color NULL exposedField SFNode normal NULL exposedField SFNode texCoord NULL field MFFloat height [] field SFBool ccw TRUE field SFBool colorPerVertex TRUE field SFFloat creaseAngle 0 field SFBool normalPerVertex TRUE field SFBool solid TRUE field SFInt32 xDimension 0 field SFFloat xSpacing 0.0 field SFInt32 zDimension 0 field SFFloat zSpacing 0.0 exposedField MFFloat distance 10 exposedField MFFloat quality [0, 0.75] }

SplineExtrusion { eventIn MFVec2f set_crossSection eventIn MFRotation set_orientation eventIn MFVec2f set_scale eventIn MFVec3f set_spine field SFBool beginCap TRUE field SFBool ccw TRUE field SFBool convex TRUE field SFFloat creaseAngle 0 field MFVec2f crossSection [1 1, 1 -1, -1 -1, -1 1, 1 1] field SFBool endCap TRUE field MFRotation orientation 0 0 1 0 field MFVec2f scale 1 1 field SFBool solid TRUE field MFVec3f spine [0 0 0, 0 1 0] field MFFloat distance 10 field MFFloat quality [0, 0.75] }

SplineFaceSet { eventIn MFInt32 set_colorIndex eventIn MFInt32 set_coordIndex eventIn MFInt32 set_normalIndex eventIn MFInt32 set_texCoordIndex exposedField SFNode color NULL exposedField SFNode coord NULL exposedField SFNode normal NULL exposedField SFNode texCoord NULL field SFBool ccw TRUE field MFInt32 colorIndex [] field SFBool colorPerVertex TRUE field SFBool convex TRUE field MFInt32 coordIndex [] field SFFloat creaseAngle 0 field MFInt32 normalIndex [] field SFBool normalPerVertex TRUE field SFBool solid TRUE field MFInt32 texCoordIndex [] exposedField MFFloat distance 10 exposedField MFFloat quality [0, 0.75] }

SplineSphere { field SFFloat radius 1 exposedField MFFloat distance 10 exposedField MFFloat quality [0, 0.75] }

The smoothing surfaces is available only if the field normalPerVertex is set to TRUE (default value) that is correspond to Gouraud method for polygonal objects. If a set of 3D surface normal vectors is defind in node(the normal field), Cortona will use it in generating of a spline surface. If the normal field is NULL, the browser treats the normals automatically generated, using the creaseAngle field (see VRML97, Node Reference). The resulted spline surface contains all of vertices defined in node, and normals per vertex coincide with normals per spline surface at vertices.

The distance and quality fields enable to control the quality of the spline surface brake down (triangulation) depending on the distance from the camera to the center of the object bounding box. The distance field specifies a set of distances to object. Each distance[i] value is correspond to the quality[i+1] value. The quality[0] value specifies the triangulation quality at distance=0. Thus, if the greatest index in the distance field is N, there shall be N+1 qualities in the quality field.

Let N denotes the greatest index in the distance field. The following equations define the current quality of the spline surface brake down:

where:
D - the distance from the camera to the center of the object bounding box.
Q - the current quality of the spline surface brake down, ranging from 0 for the worst quality to 1 for best surface.