The three main ways to get geometry out of Houdini

Houdini exports geometry through three primary routes: ROP nodes (Render Output Drivers) for batch exports, the File node for single-frame saves, and direct viewport export through the menu. Which one you use depends on whether you need one file or many, whether you're exporting during work or setting up an automated pipeline, and what format your receiving software expects.

The File node is the fastest for a quick export. ROP nodes are what you use when you need to export a sequence, bake out a simulation, or hand off work to another department. Viewport export works when you want exactly what you see on screen, without rendering or simulation steps.

All three methods support the same file formats — FBX, OBJ, Alembic, USD, and others — but they behave differently with animation, point caches, and file organization.

Key Takeaways

  • The File node is the simplest method for exporting a single frame or static geometry directly from your network.
  • ROP nodes let you export sequences and automate the process, and they're required if you need to bake simulations or export multiple frames at once.
  • Viewport export from the Geometry menu gives you what you see without going through the node network, useful for quick checks.
  • Alembic format preserves animation and point caches; OBJ and FBX work with most software but export only a single frame unless you set up a sequence.
  • File paths in Houdini use variables like $HIP and $F to organize exports by project and frame number automatically.

Using the File node for single exports

The File node is the most direct path. Go to the SOP (geometry) level where your geometry lives, create a File node, and connect it to the geometry you want to save. In the node's parameters, set the file path — for example, $HIP/geo/model.fbx — and press the save button next to the path field. Houdini writes the file immediately.

The File node exports only the current frame. If you need animation or a sequence, you'll need a ROP node instead. But for static geometry, character models, or anything you're handing off as a single file, the File node is faster than setting up a ROP.

The file format is determined by the extension you type: .fbx for FBX, .obj for OBJ, .abc for Alembic. Houdini will warn you if the format doesn't match the geometry type — for example, if you try to export animation to OBJ, which doesn't support it.

Setting up a ROP node for sequences and automation

ROP nodes live in the ROP (Render Output) context, not the SOP context. To create one, go to the ROP network (usually a tab at the top of the network editor, or create one if it doesn't exist), and add a Geometry ROP or File ROP node. Connect it to the SOP path you want to export — you do this by typing the path in the node's SOP Path parameter, for example /obj/geo1/OUT.

In the ROP node, set your file path with frame variables. Use $F for the current frame number: $HIP/geo/model_$F.fbx will create model_1.fbx, model_2.fbx, and so on. Set the frame range in the ROP node's parameters — Start Frame and End Frame — then press Render to export the whole sequence at once.

ROP nodes are also where you control whether to export animation within a single file (Alembic supports this) or as a sequence of separate files. Check the node's parameters for options like Save to Disk or Animated Geometry depending on the ROP type.

Exporting directly from the viewport

Right-click on the geometry in the viewport and select Export Geometry, or go to the Geometry menu at the top and choose Export. A file browser opens; choose your location and format. This exports exactly what you see — no node network, no parameters to set.

Viewport export is useful for quick checks or when you want to bypass the node network entirely. It respects the current viewport display settings, so if you've hidden certain geometry or toggled visibility, only the visible parts export.

This method exports a single frame only. It does not support sequences or animation.

Choosing the right file format

Alembic (.abc) preserves animation, deformation, and point caches. Use this when you're handing geometry to another Houdini artist, to a VFX pipeline, or to software that reads Alembic like Maya or Blender. Alembic files can be large but they carry the most information.

FBX (.fbx) works with game engines, 3D software, and motion capture pipelines. It supports skeletal animation and is the standard for character rigging. FBX exports a single frame unless you set up a sequence in a ROP node.

OBJ (.obj) is the simplest format and works everywhere, but it exports geometry only — no animation, no materials, no deformation. Use OBJ when you need a static model and compatibility is the priority.

USD (.usd) is newer and becoming standard in VFX and game pipelines. It supports animation, materials, and complex hierarchies. Use USD if your pipeline supports it and you need to preserve scene structure.

Using variables to organize exports automatically

Houdini file paths support variables that expand automatically. $HIP is the project directory. $F is the frame number. $OS is the node name. A path like $HIP/exports/$OS_$F.abc will create a folder called exports in your project, then save files named after the node and frame number.

Padding frame numbers is common in pipelines. Use $F4 to pad to four digits: frame 1 becomes 0001. This keeps files in alphabetical order and matches how most software expects sequences.

You can also use $JOB if you've set a job directory in your Houdini preferences, or $HIPNAME for the current file name without the path. These variables save time when you're setting up exports that need to work across multiple projects or files.

Troubleshooting common export problems

If the export fails silently, check the file path — make sure the folder exists and you have write permission. Houdini will not create parent directories automatically. If you're exporting a sequence and only one file appears, check that your ROP node's frame range is set correctly and that you pressed Render, not just Save.

If the exported geometry looks wrong, check the display flag on your nodes. The File node and ROP nodes export whatever the display flag points to, not the render flag. If you've hidden geometry in the viewport, it won't export unless you unhide it or change which node has the display flag.

For Alembic exports that seem to have lost animation, make sure the ROP node has Animated Geometry or Save to Disk enabled, and that your frame range includes all the frames you need. OBJ and FBX will only export a single frame regardless of settings — use Alembic or a sequence if you need animation.

Frequently Asked Questions

Can I export animation in a single file?

Yes, but only with Alembic. FBX and OBJ export a single frame. If you need animation in FBX, export a sequence of files instead — one per frame — and import them as a sequence in your receiving software.

How do I export only part of my geometry?

Add a null node or group node before your File or ROP node and connect only the geometry you want. Alternatively, use a Delete node to remove unwanted geometry before export. The File node and ROP nodes export whatever is connected to them.

Why is my exported file much larger than expected?

Alembic files are larger than OBJ or FBX because they store more information. If file size matters, use OBJ for static geometry or FBX for rigged models. You can also reduce polygon count before export using a Remesh or Reduce node.

Can I export with materials and textures?

FBX and USD can carry material information, but most software requires you to re-assign textures on import. OBJ and Alembic do not store materials. For game engines, export geometry only and assign materials in the engine itself.

How do I export a camera or lights along with geometry?

File and ROP nodes export geometry only. To export cameras and lights, use a USD ROP or export the entire scene as USD, which preserves the full hierarchy. For other formats, export geometry and cameras separately.