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Correctly compute contour length for wrapped contours #6102

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Dec 11, 2021
Merged

Correctly compute contour length for wrapped contours #6102

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11 changes: 8 additions & 3 deletions src/grdcontour.c
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Original file line number Diff line number Diff line change
Expand Up @@ -540,7 +540,7 @@ GMT_LOCAL void grdcontour_sort_and_plot_ticks (struct GMT_CTRL *GMT, struct PSL_
double add, dx, dy, x_back, y_back, x_front, y_front, x_end, y_end, x_lbl, y_lbl;
double xmin, xmax, ymin, ymax, inc, dist, a, this_lon, this_lat, sa, ca;
double *s = NULL, *xp = NULL, *yp = NULL;
double da, db, dc, dd;
double da, db, dc, dd, L, L_cut;

double tick_gap = I->dim[GMT_X];
double tick_length = I->dim[GMT_Y];
Expand Down Expand Up @@ -668,8 +668,13 @@ GMT_LOCAL void grdcontour_sort_and_plot_ticks (struct GMT_CTRL *GMT, struct PSL_
if (np == 0) continue;

s = gmt_M_memory (GMT, NULL, np, double); /* Compute distance along the contour */
for (j = 1, s[0] = 0.0; j < np; j++)
s[j] = s[j-1] + hypot (xp[j]-xp[j-1], yp[j]-yp[j-1]);
for (j = 1, s[0] = 0.0; j < np; j++) {
L = hypot (xp[j]-xp[j-1], yp[j]-yp[j-1]);
L_cut = gmt_half_map_width (GMT, 0.5 * (yp[j]+yp[j-1]));
if (L > L_cut) /* Eliminate horizontal jumps exceeding half mapwidth at this y-value */
L = 0.0;
s[j] = s[j-1] + L;
}
n_ticks = irint (floor (s[np-1] / tick_gap));
if (s[np-1] < GRDCONTOUR_MIN_LENGTH || n_ticks == 0) { /* Contour is too short to be ticked or labeled */
save[pol].do_it = false;
Expand Down