# Import geometry from other objects

Use the Object Merge surface node to grab geometry from other objects' geometry networks. This is useful for various purposes:

• Create piecemeal objects with subsets of an “overall” object’s geometry. For example, you can model a car all in one network, then create separate objects with the moving parts of the car for purposes of animation.

• You can also do the reverse, model parts separately and merge them together into one object.

• By importing points from two objects, you can create a new object that connects them that will work as the referenced objects move. For example, to animate a rope that a character uses to swing across a chasm, you could import points from the character’s hand and the rope attachment point, and model the rope between them.

• Object Merge is sometimes useful because it “bakes” transforms on the imported geometry (see the discussion of the Transform object parameter in the steps below).

• Anywhere else you might want to use geometry from another object, either for display or just to use its points for reference.

1. Go to the Geometry level of the object into which the geometry will be merged.

2. Use the tab menu to create an Object Merge node.

3. In the Object Merge node’s parameters, Use the merge list to choose the geometry to merge in.

You can also manually type the path to an object or SOP node, use wildcards to merge in multiple objects, use a bundle reference to merge in all objects in a bundle, use a dynamics path to merge in geometry from a dynamics simulation, and more. See the help for the Object Merge node for more information on the Object n parameter.

4. The node’s Transform object parameter is very important. It affects the transformation of the geometry as it is imported.

# Geometry

## Understanding ¶

• Describes how Houdini represents geometry using details, primitives, points, vertices, and attributes.

## Modeling ¶

• In Houdini you can not only edit the parameters of a surface node, you can reselect the geometry the operation applies to.

## Terrain ¶

• How to use Houdini’s height field tools to generate realistic terrain.

• A heuristic workflow using the heightfield tools, based on experience generating realistic-looking terrain.

## Fracturing ¶

• How to break different types of materials.

## Clouds ¶

• How to create 2D and 3D cloud patterns using the Sky Field node.

## Next steps ¶

• The appearance editor mode of the data tree pane lets you edit various controls for object viewport/rendered appearance in one place.

## Guru level ¶

• You can mark a chain of compilable SOPs as a compiled block which can execute much faster in parallel.

• Many geometry (SOP) nodes allow you to use them in Python scripts to generate geometry programmatically.

• Some nodes use a library that gives a speed boost for floating-point operations but can make the output vary between different computers. You can control how much the library tries to guarantee reproducible results.