| 1 | /* changes line 37 for Linux - Markus Neteler (Jan. 1998) */
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| 2 |
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| 3 | /*****************************************************************************/
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| 4 |
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| 5 | /*** ***/
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| 6 |
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| 7 | /*** feature() ***/
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| 8 |
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| 9 | /*** Returns a terrain feature based on the 6 quadratic coefficients ***/
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| 10 |
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| 11 | /*** that define a local trend surface. ***/
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| 12 |
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| 13 | /*** Jo Wood, Department of Geography, V2.1 30th March, 1995 ***/
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| 14 |
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| 15 | /*** ***/
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| 16 |
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| 17 | /*****************************************************************************/
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| 18 |
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| 19 | #include "param.h"
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| 20 | #include <math.h>
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| 21 |
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| 22 |
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| 23 | DCELL feature(double *coeff)
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| 24 | { /* Set of six quadratic coefficients. */
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| 25 |
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| 26 | /* Quadratic function in the form of
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| 27 |
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| 28 | z = ax^2 + by^2 + cxy + dx + ey +f */
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| 29 |
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| 30 | double a = C_A * zscale, /* Scale parameters if necessary. */
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| 31 | b = C_B * zscale,
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| 32 | c = C_C * zscale, d = C_D * zscale, e = C_E * zscale;
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| 33 |
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| 34 | double maxic, minic, /* Minimium and maximum curvature. */
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| 35 | slope, /* Slope. */
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| 36 | crosc; /* Cross-sectional curvature. */
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| 37 |
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| 38 | minic = (-a - b - sqrt((a - b) * (a - b) + c * c));
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| 39 | maxic = (-a - b + sqrt((a - b) * (a - b) + c * c));
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| 40 | slope = RAD2DEG * atan(sqrt((d * d) + (e * e)));
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| 41 | crosc = -2.0 * (b * d * d + a * e * e - c * d * e) / (d * d + e * e);
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| 42 |
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| 43 |
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| 44 | /*
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| 45 | Feature slope crosc maxic minic
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| 46 |
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| 47 | Peak 0 # +ve +ve
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| 48 | Ridge 0 # +ve 0
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| 49 | +ve +ve # #
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| 50 | Pass 0 # +ve -ve
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| 51 | Plane 0 # 0 0
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| 52 | +ve 0 # #
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| 53 | Channel 0 # 0 -ve
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| 54 | +ve -ve # #
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| 55 | Pit 0 # -ve -ve
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| 56 |
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| 57 | Table 5.3 Simplified feature classification criteria.
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| 58 | # indicates undefined, or not part of selection criteria.
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| 59 | http://www.geog.le.ac.uk/jwo/research/dem_char/thesis/05feat.htm
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| 60 | */
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| 61 |
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| 62 | /* Case 1: Surface is sloping. Cannot be a peak,pass or pit. Therefore
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| 63 | calculate the cross-sectional curvature to characterise as
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| 64 | channel, ridge or planar. */
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| 65 |
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| 66 | if (slope > slope_tol) {
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| 67 | if (crosc > curve_tol) {
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| 68 | return (RIDGE);
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| 69 | }
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| 70 | else if (crosc < -curve_tol) {
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| 71 | return (CHANNEL);
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| 72 | }
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| 73 | else {
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| 74 | return (FLAT);
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| 75 | }
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| 76 | }
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| 77 | else {
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| 78 |
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| 79 |
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| 80 | /* Case 2: Surface has (approximately) vertical slope normal. Feature
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| 81 | can be of any type. */
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| 82 |
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| 83 | if (maxic > curve_tol) {
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| 84 | if (minic > curve_tol) {
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| 85 | return (PEAK);
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| 86 | }
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| 87 | else if (minic < -curve_tol) {
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| 88 | return (PASS);
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| 89 | }
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| 90 | else {
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| 91 | return (RIDGE);
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| 92 | }
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| 93 | }
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| 94 | else if (maxic < -curve_tol) {
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| 95 | if (minic < -curve_tol) {
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| 96 | return (PIT);
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| 97 | }
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| 98 | }
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| 99 | else {
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| 100 | if (minic < -curve_tol) {
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| 101 | return (CHANNEL);
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| 102 | }
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| 103 | else if (minic > curve_tol && minic < -curve_tol) {
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| 104 | return (FLAT);
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| 105 | }
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| 106 | }
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| 107 | }
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| 108 | return (FLAT);
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| 109 | }
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