OIV.VolumeViz.Nodes.SoHeightFieldRender displays a uniform grid in the XY plane whose vertices are height (Z) values stored in 2D LDM format (any LDM data set with the Z dimension equal to 1). Adding the combination of LDM data management with advanced GPU features provides a way to handle extremely large surfaces. Just as with volume data, LDM uses tiles of data and multiple levels of resolution to enable interactive frame rates even for data sets that cannot fit in system memory.

This node is used similar to OIV.VolumeViz.Nodes.SoVolumeRender, but instead of an OIV.VolumeViz.Nodes.SoVolumeData node, you use an OIV.VolumeViz.Nodes.SoHeightFieldGeometry for the data set (height values) and one or more OIV.VolumeViz.Nodes.SoHeightFieldProperty nodes for property data sets. Generally it obeys the same rules regarding multiple data sets (see OIV.LDM.Nodes.SoMultiDataSeparator). Undefined or undesired points may be excluded by setting their value to the "undefined" value in the OIV.VolumeViz.Nodes.SoHeightFieldGeometry data set. In addition, undefined or undesired cells may be excluded by specifying a binary mask using an OIV.VolumeViz.Nodes.SoHeightFieldPropertyMask node.

Data set values are converted to height values in 3D space in two ways depending on the data type:

• Integer values are normalized between [0,1] ([-1,1] for signed types) based on the range of values for the specific data type. For example, for UNSIGNED BYTE values the range 0..255 is mapped to 0..1.

• Floating point values are not normalized (are used "as is").

Any height values in the OIV.VolumeViz.Nodes.SoHeightFieldGeometry data set that are equal to the "undefined" value will be rendered as holes in the mesh. The undefined value can be specified during the LDM conversion using the "-u" option to the LDM converter:

   convert -u 127 -b 1 inputFile.lst

An OIV.VolumeViz.Nodes.SoHeightFieldPropertyMask node may be used to specify undefined cells in the mesh. An undefined cell effectively removes the four corresponding height values from the mesh. (OIV.VolumeViz.Nodes.SoVolumeMask does not apply to height field rendering.)

  <TABLE border=1 cellspacing=0 cellpadding=5>
    <TR><TD valign=_top> @image html horizon.jpg
    <TR><TD valign=_top> A lighted heightfield
 </TABLE>

VolumeViz provides default shaders that conveniently color the surface using a single property, as shown in the images. However it is also possible to combine multiple properties using a custom shader program, in the same way that you would combine multiple volumes.

The field OIV.VolumeViz.Nodes.SoHeightFieldRender.m_cellOutline enables drawing the edges of the mesh cells. BoundaryCells are cells close to undefined value. If the OIV.VolumeViz.Nodes.SoHeightFieldRender.m_boundaryCells field is set to ALWAYS, these cells must be always considered at all resolution levels to avoid artifacts. In SMART mode, the default, we don't take this into account for distant views.

Normally this node uses the OpenGL tessellation shader extension to speed up rendering and automatically adjust the number of generated triangles depending on the camera position and orientation. In this mode, to change the number of generated triangles, use an OIV.Inventor.Nodes.SoComplexity node. A value of 1 means a full tessellation with a maximum of 4 triangles per pixel and a value of 0.5 means a maximum of 1 triangle per pixel.

If tessellation shaders are not available, use the OIV.LDM.SoLDMGlobalResourceParameters method setMaxNumTriangles() to limit the number of generated triangles. Use the OIV.Inventor.Devices.SoGLExtension method isAvailable( "GL_ARB_tessellation_shader" ) to check if tessellation shaders are supported.

Multidata rules apply to the creation of a scene graph using a OIV.VolumeViz.Nodes.SoHeightFieldRender. OIV.LDM.Nodes.SoMultiDataSeparator must be used instead of OIV.Inventor.Nodes.SoSeparator. A minimal scene graph displaying a heightfield is:

EXAMPLE

SoHeightFieldGeometry HFGeom = new SoHeightFieldGeometry();
 HFGeom.fileName.Value = "$OIVHOME/examples/data/VolumeViz/horizon.ldm";
 HFGeom.dataSetId.Value = 1;

SoHeightFieldProperty HFProp = new SoHeightFieldProperty();
 HFProp.fileName.Value = "$OIVHOME/examples/data/VolumeViz/horizon.ldm";
 HFProp.dataSetId.Value = 2;

SoMaterial Material = new SoMaterial();
 Material.diffuseColor.SetValue(1, 1, 1);

SoTransferFunction TF = new SoTransferFunction();
 TF.predefColorMap.Value = SoTransferFunction.PredefColorMaps.STANDARD;

SoHeightFieldRender HFRend = new SoHeightFieldRender();

SoComplexity Complexity = new SoComplexity();
 Complexity.value.Value = 0.25;

SoMultiDataSeparator volSep = new SoMultiDataSeparator();
 volSep.AddChild(HFGeom);
 volSep.AddChild(HFProp);
 volSep.AddChild(Material);
 volSep.AddChild(Complexity);
 volSep.AddChild(TF);
 volSep.AddChild(HFRend);
root.AddChild( volSep );

Shaders

When used with an OIV.VolumeViz.Nodes.SoVolumeShader, a new shader function is available to compute lighting:

• vec4 VVizComputeFrontColor(vec3 normal, vec4 color)): Add lighting to the color col.

The following shader code code will light a heightfield:

vec4 VVizComputeVolumeRendering(float sf);
float VVizCombineData(vec2 tcoord);
vec3 VVizComputeCoordinates(const vec3);
void VVizOutputColor(vec4 color);
vec4 VVizComputeFrontColor(vec3 n, vec4 col);
vec3 VVizComputeGradient(vec3 tcoord);

void main()
{
 vec3 tCoord0 = VVizComputeCoordinates(gl_TexCoord[0].xyz);
 vec3 grad = VVizComputeGradient(tCoord0);
 vec3 normal = normalize(gl_NormalMatrix*grad);

 float sf = VVizCombineData(tCoord0.xy);
 vec4 col = VVizComputeVolumeRendering(sf);

 col = VVizComputeFrontColor(normal, col);*
 VVizOutputColor(col);
}

Similar to other geometry, OIV.Inventor.SoPickedPoint can return an OIV.Inventor.Details.SoDetail object specific to the OIV.VolumeViz.Nodes.SoHeightFieldRender node. The specific class is OIV.VolumeViz.Details.SoHeightFieldDetail.

Only GPU picking is supported. This means that the OIV.Inventor.Actions.SoRayPickAction used for picking must have its scene manager initialized using the method OIV.Inventor.Actions.SoAction.SetSceneManager(OIV.Inventor.SoSceneManager). OIV.Inventor.Actions.SoHandleEventAction does this automatically, so it is not necessary for the application to take any action when using (for example) a OIV.Inventor.Nodes.SoEventCallback node and calling the getPickedPoint() method. However if the application creates its own OIV.Inventor.Actions.SoRayPickAction then it must set the scene manager. If no scene manager is specified, a warning message is issued.

Limitations:

• At least one OIV.VolumeViz.Nodes.SoHeightFieldProperty which defines a property data set associated with the grid must be in the state.

• If an OIV.LDM.Nodes.SoROI is in the state, OIV.VolumeViz.Nodes.SoHeightFieldRender renders only one box of the ROI (ie: correct rendering only if OIV.LDM.Nodes.SoROI's flag field is set to SUB_VOLUME)

• Only OIV.VolumeViz.Nodes.SoHeightFieldGeometry data sets with a depth of 1 (Z dimension = 1) can be rendered.

• The OIV.VolumeViz.Nodes.SoHeightFieldProperty and OIV.VolumeViz.Nodes.SoHeightFieldPropertyMask data sets must have exactly the same dimensions as the OIV.VolumeViz.Nodes.SoHeightFieldGeometry.

• Triangle orientation after GPU tessellation cannot be controlled. Undefined value rendering is indeterministic.

• For low resolution, undefined values can be taken into account in the property but not in the geometry. In such cases, coloring artifacts can appear.

• Lighting is limited to directional lights and base color. Other kinds of lights can be implemented manually using a custom shader.

• By default, two-sided lighting is not enabled ("back" side of surface will not be lighted). Use an OIV.Inventor.Nodes.SoShapeHints node to enable two-sided lighting.

• The OIV.VolumeViz.Nodes.SoSlice.m_enableBumpMapping field is not supported on this node

• OIV.VolumeViz.Nodes.SoHeightFieldPropertyMask and OIV.VolumeViz.Nodes.SoHeightFieldRender.m_cellOutline can be used only if tesselation shaders are supported. Use the OIV.Inventor.Devices.SoGLExtension method isAvailable( "GL_ARB_tessellation_shader" ) to check this support.

FILE FORMAT/DEFAULT

HeightFieldRender {

enableBumpMapping	false
bumpScale	1.0
alternateRep	NULL
useRGBA	false
cellOutline	false

}

Reference