int cyclic(unsigned char **sec) {
int grid_template, nx, ny, res, scan, flag_3_3, no_dx, basic_ang, sub_ang;
unsigned int npnts;
unsigned char *gds;
double dlon, units, lon1, lon2;
get_nxny(sec, &nx, &ny, &npnts, &res, &scan);
if (GDS_Scan_staggered(scan)) return 0;
if (nx <= 1 || ny <= 0) return 0;
grid_template = code_table_3_1(sec);
gds = sec[3];
flag_3_3 = flag_table_3_3(sec);
no_dx = 0;
if (flag_3_3 != -1) {
if ((flag_3_3 & 0x20) == 0) no_dx = 1;
}
if (no_dx) return 0;
if (grid_template == 0) {
basic_ang = GDS_LatLon_basic_ang(gds);
sub_ang = GDS_LatLon_sub_ang(gds);
units = basic_ang == 0 ? 0.000001 : (double) basic_ang / (double) sub_ang;
/* dlon has to be defined */
dlon = units * GDS_LatLon_dlon(gds);
return (fabs(nx*dlon-360.0) < ERROR);
}
if (grid_template == 10) {
if (output_order != wesn) return 0; // only works with we:sn order
lon1 = GDS_Mercator_lon1(gds);
lon2 = GDS_Mercator_lon2(gds);
if (lon2 < lon1) lon2 += 360.0;
dlon = (lon2-lon1)*nx/(nx-1.0);
return (fabs(dlon-360.0) < ERROR);
}
if (grid_template == 40) {
basic_ang = GDS_Gaussian_basic_ang(gds);
sub_ang = GDS_Gaussian_sub_ang(gds);
units = basic_ang == 0 ? 0.000001 : (double) basic_ang / (double) sub_ang;
/* dlon has to be defined */
dlon = units * GDS_Gaussian_dlon(gds);
return (fabs(nx*dlon-360.0) < ERROR);
}
return 0;
}
int mercator2ll(unsigned char **sec, double **lat, double **lon) {
double dx, dy, lat1, lat2, lon1, lon2;
double *llat, *llon;
int i, j;
unsigned int k;
double dlon, circum;
double n,s,e,w,tmp,error;
unsigned char *gds;
int nnx, nny, nres, nscan;
unsigned int nnpnts;
get_nxny(sec, &nnx, &nny, &nnpnts, &nres, &nscan);
gds = sec[3];
dy = GDS_Mercator_dy(gds);
dx = GDS_Mercator_dx(gds);
lat1 = GDS_Mercator_lat1(gds);
lat2 = GDS_Mercator_lat2(gds);
lon1 = GDS_Mercator_lon1(gds);
lon2 = GDS_Mercator_lon2(gds);
if (lon1 < 0.0 || lon2 < 0.0 || lon1 > 360.0 || lon2 > 360.0) fatal_error("BAD GDS lon","");
if (lat1 < -90.0 || lat2 < -90.0 || lat1 > 90.0 || lat2 > 90.0) fatal_error("BAD GDS lat","");
if (GDS_Mercator_ori_angle(gds) != 0.0) {
fprintf(stderr,"cannot handle non-zero mercator orientation angle %f\n",
GDS_Mercator_ori_angle(gds));
return 0;
}
if (nnx == -1 || nny == -1) {
fprintf(stderr,"Sorry geo/mercator code does not handle variable nx/ny yet\n");
return 0;
}
if ((*lat = (double *) malloc(nnpnts * sizeof(double))) == NULL) {
fatal_error("mercator2ll memory allocation failed","");
}
if ((*lon = (double *) malloc(nnpnts * sizeof(double))) == NULL) {
fatal_error("mercator2ll memory allocation failed","");
}
/* now figure out the grid coordinates mucho silly grib specification */
/* find S and N latitude */
if (GDS_Scan_y(nscan)) {
s = lat1;
n = lat2;
}
else {
s = lat2;
n = lat1;
}
if (s > n) fatal_error("Mercator grid: lat1 and lat2","");
/* find W and E longitude */
if ( ((nscan & 16) == 16) && (nny % 2 == 0) && ((nres & 32) == 0) ) {
fatal_error("grib GDS ambiguity","");
}
if ( ((nscan & 16) == 16) && (nny % 2 == 0) ) {
fatal_error("more code needed to decode GDS","");
}
if (GDS_Scan_x(nscan)) {
w = lon1;
e = lon2;
} else {
w = lon2;
e = lon1;
}
if (e <= w) e += 360.0;
llat = *lat;
llon = *lon;
dlon = (e-w) / (nnx-1);
circum = 2.0 * M_PI * radius_earth(sec) * cos(GDS_Mercator_latD(gds) * (M_PI/180.0));
dx = dx * 360.0 / circum;
// dlon should be almost == to dx
// replace dx by dlon to get end points to match
if (dx != 0.0) {
error = fabs(dx-dlon) / fabs(dx);
if (error >= 0.001) { fprintf(stderr,
"\n*** Mercator grid error: inconsistent d-longitude, radius and grid domain\n"
"*** d-longitude from grid domain %lf (used), d-longitude from dx %lf (not used)\n",
dlon, dx);
}
dx = dlon;
}
s = log(tan((45+s/2)*M_PI/180));
n = log(tan((45+n/2)*M_PI/180));
dy = (n - s) / (nny - 1);
for (j = 0; j < nny; j++) {
tmp = (atan(exp(s+j*dy))*180/M_PI-45)*2;
for (i = 0; i < nnx; i++) {
*llat++ = tmp;
}
}
for (j = 0; j < nnx; j++) {
llon[j] = w + j*dx >= 360.0 ? w + j*dx - 360.0 : w + j*dx;
}
for (k = nnx; k < nnpnts; k++) {
llon[k] = llon[k-nnx];
}
return 0;
} /* end mercator2ll() */
