... +a11xy +a21x2y +a 31 x 3 y+a02y2+a12xy2+a22x2y2+a 32 x 3 y2+a 03 y 3 +a 13 xy 3 +a 23 x2y 3 +a 33 x 3 y 3 (6.9)where a00, a01, a10, , a 33 are the 16 coefficients ... CRC PressDITM: “tf1 732 _c006” — 2004/10/20 — 15:44 — page 132 — #18 132 DIGITAL TERRAIN MODELING: PRINCIPLES AND METHODOLOGY P1P2P2P 3 P1P 3 P1P2P2P 3 P1P 3 (a) (b)(c) (d)Figure ... 6 .3 shows this trend, where a set of values for σ (i.e., 0, 0.6, and 10) were 3 2101 234 diQ (di ) =0 3 2101 234 567xz 3 2101 234 diQ (di ) =0.6 3 2101 234 567xz 3 2101 234 diQ...