The decimation filter retains every Nth point from an input point view.
<?xml version="1.0" encoding="utf-8"?>
<Pipeline version="1.0">
<Writer type="writers.las">
<Option name="filename">smaller.las</Option>
<Filter type="filters.decimation">
<Option name="step">10</Option>
<Reader type="readers.las">
<Option name="filename">larger.las</Option>
</Reader>
</Filter>
</Writer>
</Pipeline>
See also
filters.voxelgrid provides grid-style point decimation.