height_field{ png "plasma3.png" smooth double_illuminate
              // file types: 
              // gif | tga | pot | png | pgm | ppm | jpeg | tiff | sys
              // [water_level N] // truncate/clip below N (0.0 ... 1.0)
              translate<-0.5, -1,0>
              scale<6,-3, 6> 
              texture{ pigment { color rgb <0.85,0.6,0.4>}
                       normal  { bumps 0.75 scale 0.025  }
                     } // end of texture
              rotate<0,0,0>
              translate<0,-1,0>
            } // end of height_field ----------------------------------
