Houdini 12 Nodes Surface nodes

Lets you paste local refinements on top of base NURBS geometry.

## Introduction

The Paste op is a local refinement tool that doesn’t increase the complexity of the base surface, yet allows detail to move freely on the base surface.

A feature of the Paste op is that regardless of the pasting method, the base hierarchy will always keep its primitive numbers. The features will be added to the existing model, so their numbers will always be higher than those of the base(s). This allows you to change the resolution of the animation at the base level and animate base points at various resolutions without worrying about point-number changes.

## Two Ways of Building a Paste Hierarchy

There are two ways of building a paste hierarchy; from outside the base surface, and from inside the base surface.

This is done using the Paste op, with two inputs: the feature and the base.

• Parametric Paste

• Along Vector (Projective) Paste

1. In a Parametric Paste, the Paste op places the feature on an area of the base surface delimited by four user-defined isoparametric curves. The feature is thus aligned with the base surface isoparametrically.

The advantage of Parametric Pasting is that the feature is guaranteed to “land” on the base within a well determined parametric area regardless of the base’s shape, position and orientation; also, the continuity between feature and base is enhanced by the parametric alignment between the two surfaces.

2. In a Projective Paste, the four corners of the feature surface are projected onto the base surface first. Then the entire feature is moulded onto the base such that its corners match the four projected points. The feature is not aligned with the base isoparametrically.

The advantage of the Projective Paste is that it applies the feature onto the base intuitively along a vector, without any parametric alignment, generally producing a mould that is similar in shape and orientation to the original (unpasted feature).

### Growing Detail from Within

If you use only one input to the Paste op, you can still create a pasted surface using a method called “spawning”. This technique extracts a portion of the base surface and turns it into a pasted surface that shares the base’s shape and underlying domain in that area (much like an onion peel).

The new surface can be further refined and modeled to generate the desired detail; it can be spawned recursively to add even more detail. This new surface may be lofted above the base surface by the amount specified by the Height parameter. This is an easy way to build offset surfaces. The advantage of the spawning technique is that it guarantees perfect geometric and texture continuity between feature and base.

## Some Notes on Getting Good Pasted Surfaces

• The flatter the base surface, the less distorted the pasted surface will be.

• The more tentacles on the feature surface (i.e. the more refined the feature), the better its moulding on the base surface.

• The more vertical the initial tentacles, the more closely the pasted surface will follow the features of the base.

• The shorter the tentacle, the closer to the base surface it will be. Therefore, in general it is better to start with a flat base surface, and deform it in the middle, leaving the edges so their slope is flat. This yields better boundary continuity across feature and surface.

• It is also good to ensure that the feature starts out as a rectangular grid and all the interior deformations don’t “spill-out” of the rectangular area.

Tip

If the feature doesn’t have enough resolution (i.e. tentacles), you may have a problem with boundary continuity, in which case you can add a Refine SOP to the feature before doing the paste, or increase the number of boundary isoparms with the Belt parameters.

## Surface Deletion

You can delete surfaces with Delete SOP and Unpaste SOP, as well as in the view.

## Current Limitations

• You cannot paste across multiple paste hierarchies.

• Most, but not all ops support the “Pasted” primitive type. Those that do not will either ignore the hierarchical primitive or delete it.

## Tips

Use the Paste op to create a continuous surface which covers multiple surfaces and seams by pasting a flat dense NURBS grid over the entire paste hierarchy with a parametric range of U=0-1, V=0-1. This makes for easier texturing as you avoid the problems associated with texturing over seams. You could also achieve a similar effect by running the geometry through a Convert SOP.

## Example File

Look in: \$HD/SOPs/Pasting/head.hip for an example file.

## Parameters

Feature Group

Subset of spline surfaces or hierarchies to paste

Base Group

A single spline surface or paste hierarchy

Operation

Method of adding detail to the base surface:

 Paste Apply the feature(s) on top of the base hierarchy Insert Squeeze the features(s) between layers of the hierarchy Insert Nested Squeeze the features between nested hierarchy layers
Height

Amount of elevation from the base surface

Flip Pasting Direction

Invert pasting direction to create bumps or dents

Trim Base

Trim out the part of the base under the feature; it has the option to scale the trim profile

Belt Width

Area along feature boundary to refine

Belt Divisions

Number of U/V refinements in the belt

### Along Vector

Overview

Corners of feature surface projected along vector

Projection Axis

Choice of several projection axes:

 X, Y, Z X, Y or Z axis Feature Normal Along the primitive normal of the feature Minimum Distance Along the vectors of minimum distance to the base User Defined: Enter vector into the field below /vector1 /vector2 /vector3
Ray Tolerance

precision of ray-surface intersection

### Parametrically

 Overview Feature will cover an iso-parametric area on base U Range Area of the unit U domain to be mapped on V Range Area of the unit V domain to be mapped on

### As Is

 Overview No effort will be made to land feature onto base Keep Unpasted Shape Do not change the position or shape of the feature

## Examples

 PasteCones Load | Launch `.../examples/nodes/sop/paste/PasteCones.otl`This example shows how to use the Paste SOP to paste a series of cones onto a flat surface. In this case, a cone is copied onto the points of a decagon. The copied cones are then pasted onto the decagon so they appear to be a single surface. PasteNose Load | Launch `.../examples/nodes/sop/paste/PasteNose.otl`This Example file illustrates how the Paste SOP can be used to add to detail to a small part of a sphere. A Sphere is given a texture map, and then has extra detailed geometry attached to it. Normally this would break the texture coordinates, but with the Paste SOP and a few other key SOPs, the map coordinates are preserved.

## Examples that use this node

Example forExample name

`.../examples/nodes/sop/convert/PasteConvertVariations.otl`

`.../examples/nodes/sop/convert/PastedHeirarchy.otl`
`.../examples/nodes/sop/polyloft/PolyLoftPaste.otl`