Ocean Spectrum is a basic node for Houdini's ocean dynamics and provides basic information of the ocean waves. It uses a grid-based method (more likely FFT method but we have no evidence yet) to simulate so it does not need a DOP network to work. Ocean spectrum also supports masking and wave instancing by points. The result of multiple ocean spectrum can be accumulated and will be calculated in Ocean Evaluate node.
Create an Ocean
The easiest way to get started is to click Small Ocean in the shelf tool to create an ocean system. You will see ocean_surface node, which is the main part of the ocean, and ocean_interior node, which is used for volume rendering. Look into ocean_surface and you will find the preview node and the render node are separated by default. All the basic settings are in the Ocean Spectrum node and the grid size can be set in the render_grid node. When necessary, increase Resolution Exponent to get a more detailed ocean.
Ocean spectrum supports two ways to instance waves. You can pass points directly to ocean spectrum to generate waves based on these points. Additionally, you can merge with Ocean Waves node to create a wave.
Different from other dynamic systems, the ocean render requires baking displacement geometries/textures before rendering. Select the save_spectra node, set frame range and click Save to Disk. Then you will see the spectrum geometry containing displacement information is rendered correctly. Check Ocean Rendering page for more information.