@Override
    public void setMagnificationFilter(float filter) throws Exception {
        if (filter < 0 || filter >= 1) {
            throw new Exception("filter must be between 0 and 1");
        }
        this.filter = filter;
    }
<code>setFilter</code> sets the erosion value for the filter. This
value must be between 0 and 1, where 0.2 - 0.4 produces arguably the best
results.

@param filter
           the erosion value.
@throws Exception
            if filter is less than 0 or greater than 1.
jme3-terrain/src/main/java/com/jme3/terrain/heightmap/AbstractHeightMap.java