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#include <stdio.h>
#include <math.h>
#include "../main.hh"
#include "los.hh"
#include "cost.hh"
#include "ecc33.hh"
#include "ericsson.hh"
#include "fspl.hh"
#include "hata.hh"
#include "itwom3.0.hh"
#include "sui.hh"
#include "pel.hh"
#include "egli.hh"
#include "soil.hh"
#include <pthread.h>
#define NUM_SECTIONS 4
namespace {
pthread_t threads[NUM_SECTIONS];
unsigned int thread_count = 0;
pthread_mutex_t maskMutex;
bool ***processed;
bool has_init_processed = false;
struct propagationRange {
double min_west, max_west, min_north, max_north;
double altitude;
bool eastwest, los, use_threads;
site source;
unsigned char mask_value;
FILE *fd;
int propmodel, knifeedge, pmenv;
};
void* rangePropagation(void *parameters)
{
propagationRange *v = (propagationRange*)parameters;
if(v->use_threads) {
alloc_elev();
alloc_path();
}
double minwest = dpp + (double)v->min_west;
double lon = v->eastwest ? minwest : v->min_west;
double lat = v->min_north;
int y = 0;
do {
if (lon >= 360.0)
lon -= 360.0;
site edge;
edge.lat = lat;
edge.lon = lon;
edge.alt = v->altitude;
if(v->los)
PlotLOSPath(v->source, edge, v->mask_value, v->fd);
else
PlotPropPath(v->source, edge, v->mask_value, v->fd, v->propmodel,
v->knifeedge, v->pmenv);
++y;
if(v->eastwest)
lon = minwest + (dpp * (double)y);
else
lat = (double)v->min_north + (dpp * (double)y);
} while ( v->eastwest
? (LonDiff(lon, (double)v->max_west) <= 0.0)
: (lat < (double)v->max_north) );
if(v->use_threads) {
free_elev();
free_path();
}
return NULL;
}
void init_processed()
{
int i;
int x;
int y;
processed = new bool **[MAXPAGES];
for (i = 0; i < MAXPAGES; i++) {
processed[i] = new bool *[ippd];
for (x = 0; x < ippd; x++)
processed[i][x] = new bool [ippd];
}
for (i = 0; i < MAXPAGES; i++) {
for (x = 0; x < ippd; x++) {
for (y = 0; y < ippd; y++)
processed[i][x][y] = false;
}
}
has_init_processed = true;
}
bool can_process(double lat, double lon)
{
/* Lines, text, markings, and coverage areas are stored in a
mask that is combined with topology data when topographic
maps are generated by ss. This function sets bits in
the mask based on the latitude and longitude of the area
pointed to. */
int x, y, indx;
char found;
bool rtn = false;
for (indx = 0, found = 0; indx < MAXPAGES && found == 0;) {
x = (int)rint(ppd * (lat - dem[indx].min_north));
y = mpi - (int)rint(yppd * (LonDiff(dem[indx].max_west, lon)));
if (x >= 0 && x <= mpi && y >= 0 && y <= mpi)
found = 1;
else
indx++;
}
if (found) {
/* As long as we only set this without resetting it we can
check outside a mutex first without worrying about race
conditions. But we must lock the mutex before updating the
value. */
if(!processed[indx][x][y]) {
pthread_mutex_lock(&maskMutex);
if(!processed[indx][x][y]) {
rtn = true;
processed[indx][x][y] = true;
}
pthread_mutex_unlock (&maskMutex);
}
}
return rtn;
}
void beginThread(void *arg)
{
if(!has_init_processed)
init_processed();
int rc = pthread_create(&threads[thread_count], NULL, rangePropagation, arg);
if (rc)
fprintf(stderr,"ERROR; return code from pthread_create() is %d\n", rc);
else
++thread_count;
}
void finishThreads()
{
void* status;
for(unsigned int i=0; i<thread_count; i++) {
int rc = pthread_join(threads[i], &status);
if (rc)
fprintf(stderr,"ERROR; return code from pthread_join() is %d\n", rc);
}
thread_count = 0;
}
}
/*
* Acute Angle from Rx point to an obstacle of height (opp) and
* distance (adj)
*/
static double incidenceAngle(double opp, double adj)
{
return atan2(opp, adj) * 180 / PI;
}
/*
* Knife edge diffraction:
* This is based upon a recognised formula like Huygens, but trades
* thoroughness for increased speed which adds a proportional diffraction
* effect to obstacles.
*/
static double ked(double freq, double rxh, double dkm)
{
double obh, obd, rxobaoi = 0, d;
obh = 0; // Obstacle height
obd = 0; // Obstacle distance
dkm = dkm * 1000; // KM to metres
// walk along path
for (int n = 2; n < (dkm / elev[1]); n++) {
d = (n - 2) * elev[1]; // no of points * delta = km
//Find dip(s)
if (elev[n] < obh) {
// Angle from Rx point to obstacle
rxobaoi =
incidenceAngle((obh - (elev[n] + rxh)), d - obd);
} else {
// Line of sight or higher
rxobaoi = 0;
}
//note the highest point
if (elev[n] > obh) {
obh = elev[n];
obd = d;
}
}
if (rxobaoi >= 0) {
return (rxobaoi / (300 / freq))+3; // Diffraction angle divided by wavelength (m)
} else {
return 1;
}
}
void PlotLOSPath(struct site source, struct site destination, char mask_value,
FILE *fd)
{
/* This function analyzes the path between the source and
destination locations. It determines which points along
the path have line-of-sight visibility to the source.
Points along with path having line-of-sight visibility
to the source at an AGL altitude equal to that of the
destination location are stored by setting bit 1 in the
mask[][] array, which are displayed in green when PPM
maps are later generated by ss. */
char block;
int x, y;
register double cos_xmtr_angle, cos_test_angle, test_alt;
double distance, rx_alt, tx_alt;
ReadPath(source, destination);
for (y = 0; (y < (path.length - 1) && path.distance[y] <= max_range);
y++) {
//for (y = 0; y < path.length; y++) {
/* Test this point only if it hasn't been already
tested and found to be free of obstructions. */
if ((GetMask(path.lat[y], path.lon[y]) & mask_value) == 0
&& can_process(path.lat[y], path.lon[y])) {
distance = FEET_PER_MILE * path.distance[y];
tx_alt = earthradius + source.alt + path.elevation[0];
rx_alt =
earthradius + destination.alt + path.elevation[y];
/* Calculate the cosine of the elevation of the
transmitter as seen at the temp rx point. */
cos_xmtr_angle =
((rx_alt * rx_alt) + (distance * distance) -
(tx_alt * tx_alt)) / (2.0 * rx_alt * distance);
for (x = y, block = 0; x >= 0 && block == 0; x--) {
distance =
FEET_PER_MILE * (path.distance[y] -
path.distance[x]);
test_alt =
earthradius + (path.elevation[x] ==
0.0 ? path.
elevation[x] : path.
elevation[x] + clutter);
cos_test_angle =
((rx_alt * rx_alt) + (distance * distance) -
(test_alt * test_alt)) / (2.0 * rx_alt *
distance);
/* Compare these two angles to determine if
an obstruction exists. Since we're comparing
the cosines of these angles rather than
the angles themselves, the following "if"
statement is reversed from what it would
be if the actual angles were compared. */
if (cos_xmtr_angle >= cos_test_angle)
block = 1;
}
if (block == 0)
OrMask(path.lat[y], path.lon[y], mask_value);
}
}
}
void PlotPropPath(struct site source, struct site destination,
unsigned char mask_value, FILE * fd, int propmodel,
int knifeedge, int pmenv)
{
int x, y, ifs, ofs, errnum;
char block = 0, strmode[100];
double loss, azimuth, pattern = 0.0,
xmtr_alt, dest_alt, xmtr_alt2, dest_alt2,
cos_rcvr_angle, cos_test_angle = 0.0, test_alt,
elevation = 0.0, distance = 0.0, four_thirds_earth,
field_strength = 0.0, rxp, dBm, diffloss;
struct site temp;
float dkm;
ReadPath(source, destination);
four_thirds_earth = FOUR_THIRDS * EARTHRADIUS;
for (x = 1; x < path.length - 1; x++)
elev[x + 2] =
(path.elevation[x] ==
0.0 ? path.elevation[x] * METERS_PER_FOOT : (clutter +
path.
elevation[x])
* METERS_PER_FOOT);
/* Copy ending points without clutter */
elev[2] = path.elevation[0] * METERS_PER_FOOT;
elev[path.length + 1] =
path.elevation[path.length - 1] * METERS_PER_FOOT;
/* Since the only energy the Longley-Rice model considers
reaching the destination is based on what is scattered
or deflected from the first obstruction along the path,
we first need to find the location and elevation angle
of that first obstruction (if it exists). This is done
using a 4/3rds Earth radius to match the model used by
Longley-Rice. This information is required for properly
integrating the antenna's elevation pattern into the
calculation for overall path loss. */
//if(debug)
// fprintf(stderr,"four_thirds_earth %.1f source.alt %.1f path.elevation[0] %.1f\n",four_thirds_earth,source.alt,path.elevation[0]);
for (y = 2; (y < (path.length - 1) && path.distance[y] <= max_range);
y++) {
/* Process this point only if it
has not already been processed. */
if ( (GetMask(path.lat[y], path.lon[y]) & 248) !=
(mask_value << 3) && can_process(path.lat[y], path.lon[y])) {
char fd_buffer[64];
int buffer_offset = 0;
distance = FEET_PER_MILE * path.distance[y];
xmtr_alt =
four_thirds_earth + source.alt + path.elevation[0];
dest_alt =
four_thirds_earth + destination.alt +
path.elevation[y];
dest_alt2 = dest_alt * dest_alt;
xmtr_alt2 = xmtr_alt * xmtr_alt;
/* Calculate the cosine of the elevation of
the receiver as seen by the transmitter. */
cos_rcvr_angle =
((xmtr_alt2) + (distance * distance) -
(dest_alt2)) / (2.0 * xmtr_alt * distance);
if (cos_rcvr_angle > 1.0)
cos_rcvr_angle = 1.0;
if (cos_rcvr_angle < -1.0)
cos_rcvr_angle = -1.0;
if (got_elevation_pattern || fd != NULL) {
/* Determine the elevation angle to the first obstruction
along the path IF elevation pattern data is available
or an output (.ano) file has been designated. */
for (x = 2, block = 0; (x < y && block == 0);
x++) {
distance = FEET_PER_MILE * path.distance[x];
test_alt =
four_thirds_earth +
(path.elevation[x] ==
0.0 ? path.elevation[x] : path.
elevation[x] + clutter);
/* Calculate the cosine of the elevation
angle of the terrain (test point)
as seen by the transmitter. */
cos_test_angle =
((xmtr_alt2) +
(distance * distance) -
(test_alt * test_alt)) / (2.0 *
xmtr_alt
*
distance);
if (cos_test_angle > 1.0)
cos_test_angle = 1.0;
if (cos_test_angle < -1.0)
cos_test_angle = -1.0;
/* Compare these two angles to determine if
an obstruction exists. Since we're comparing
the cosines of these angles rather than
the angles themselves, the sense of the
following "if" statement is reversed from
what it would be if the angles themselves
were compared. */
if (cos_rcvr_angle >= cos_test_angle)
block = 1;
}
if (block)
elevation =
((acos(cos_test_angle)) / DEG2RAD) -
90.0;
else
elevation =
((acos(cos_rcvr_angle)) / DEG2RAD) -
90.0;
}
/* Determine attenuation for each point along the
path using a prop model starting at y=2 (number_of_points = 1), the
shortest distance terrain can play a role in
path loss. */
elev[0] = y - 1; /* (number of points - 1) */
/* Distance between elevation samples */
elev[1] =
METERS_PER_MILE * (path.distance[y] -
path.distance[y - 1]);
if (path.elevation[y] < 1) {
path.elevation[y] = 1;
}
dkm = (elev[1] * elev[0]) / 1000; // km
switch (propmodel) {
case 1:
// Longley Rice ITM
point_to_point_ITM(source.alt * METERS_PER_FOOT,
destination.alt *
METERS_PER_FOOT,
LR.eps_dielect,
LR.sgm_conductivity,
LR.eno_ns_surfref,
LR.frq_mhz, LR.radio_climate,
LR.pol, LR.conf, LR.rel,
loss, strmode, errnum);
break;
case 3:
//HATA 1, 2 & 3
loss =
HATApathLoss(LR.frq_mhz, source.alt * METERS_PER_FOOT,
(path.elevation[y] * METERS_PER_FOOT) + (destination.alt * METERS_PER_FOOT), dkm, pmenv);
break;
case 4:
// ECC33
loss =
ECC33pathLoss(LR.frq_mhz, source.alt * METERS_PER_FOOT,
(path.elevation[y] *
METERS_PER_FOOT) +
(destination.alt *
METERS_PER_FOOT), dkm,
pmenv);
break;
case 5:
// SUI
loss =
SUIpathLoss(LR.frq_mhz, source.alt * METERS_PER_FOOT,
(path.elevation[y] *
METERS_PER_FOOT) +
(destination.alt *
METERS_PER_FOOT), dkm, pmenv);
break;
case 6:
// COST231-Hata
loss =
COST231pathLoss(LR.frq_mhz, source.alt * METERS_PER_FOOT,
(path.elevation[y] *
METERS_PER_FOOT) +
(destination.alt *
METERS_PER_FOOT), dkm,
pmenv);
break;
case 7:
// ITU-R P.525 Free space path loss
loss = FSPLpathLoss(LR.frq_mhz, dkm);
break;
case 8:
// ITWOM 3.0
point_to_point(source.alt * METERS_PER_FOOT,
destination.alt *
METERS_PER_FOOT, LR.eps_dielect,
LR.sgm_conductivity,
LR.eno_ns_surfref, LR.frq_mhz,
LR.radio_climate, LR.pol,
LR.conf, LR.rel, loss, strmode,
errnum);
break;
case 9:
// Ericsson
loss =
EricssonpathLoss(LR.frq_mhz, source.alt * METERS_PER_FOOT,
(path.elevation[y] *
METERS_PER_FOOT) +
(destination.alt *
METERS_PER_FOOT), dkm,
pmenv);
break;
case 10:
// Plane earth
loss = PlaneEarthLoss(dkm, source.alt * METERS_PER_FOOT, (path.elevation[y] * METERS_PER_FOOT) + (destination.alt * METERS_PER_FOOT));
break;
case 11:
// Egli VHF/UHF
loss = EgliPathLoss(LR.frq_mhz, source.alt * METERS_PER_FOOT, (path.elevation[y] * METERS_PER_FOOT) + (destination.alt * METERS_PER_FOOT),dkm);
break;
case 12:
// Soil
loss = SoilPathLoss(LR.frq_mhz, dkm, LR.eps_dielect);
break;
default:
point_to_point_ITM(source.alt * METERS_PER_FOOT,
destination.alt *
METERS_PER_FOOT,
LR.eps_dielect,
LR.sgm_conductivity,
LR.eno_ns_surfref,
LR.frq_mhz, LR.radio_climate,
LR.pol, LR.conf, LR.rel,
loss, strmode, errnum);
}
if (knifeedge == 1 && propmodel > 1) {
diffloss =
ked(LR.frq_mhz,
destination.alt * METERS_PER_FOOT, dkm);
loss += (diffloss); // ;)
}
//Key stage. Link dB for p2p is returned as 'loss'.
temp.lat = path.lat[y];
temp.lon = path.lon[y];
azimuth = (Azimuth(source, temp));
if (fd != NULL)
buffer_offset += sprintf(fd_buffer+buffer_offset,
"%.7f, %.7f, %.3f, %.3f, ",
path.lat[y], path.lon[y], azimuth,
elevation);
/* If ERP==0, write path loss to alphanumeric
output file. Otherwise, write field strength
or received power level (below), as appropriate. */
if (fd != NULL && LR.erp == 0.0)
buffer_offset += sprintf(fd_buffer+buffer_offset,
"%.2f", loss);
/* Integrate the antenna's radiation
pattern into the overall path loss. */
x = (int)rint(10.0 * (10.0 - elevation));
if (x >= 0 && x <= 1000) {
azimuth = rint(azimuth);
pattern =
(double)LR.antenna_pattern[(int)azimuth][x];
if (pattern != 0.0) {
pattern = 20.0 * log10(pattern);
loss -= pattern;
}
}
if (LR.erp != 0.0) {
if (dbm) {
/* dBm is based on EIRP (ERP + 2.14) */
rxp =
LR.erp /
(pow(10.0, (loss - 2.14) / 10.0));
dBm = 10.0 * (log10(rxp * 1000.0));
if (fd != NULL)
buffer_offset += sprintf(fd_buffer+buffer_offset,
"%.3f", dBm);
/* Scale roughly between 0 and 255 */
ifs = 200 + (int)rint(dBm);
if (ifs < 0)
ifs = 0;
if (ifs > 255)
ifs = 255;
ofs =
GetSignal(path.lat[y], path.lon[y]);
if (ofs > ifs)
ifs = ofs;
PutSignal(path.lat[y], path.lon[y],
(unsigned char)ifs);
}
else {
field_strength =
(139.4 +
(20.0 * log10(LR.frq_mhz)) -
loss) +
(10.0 * log10(LR.erp / 1000.0));
ifs = 100 + (int)rint(field_strength);
if (ifs < 0)
ifs = 0;
if (ifs > 255)
ifs = 255;
ofs =
GetSignal(path.lat[y], path.lon[y]);
if (ofs > ifs)
ifs = ofs;
PutSignal(path.lat[y], path.lon[y],
(unsigned char)ifs);
if (fd != NULL)
buffer_offset += sprintf(fd_buffer+buffer_offset,
"%.3f",
field_strength);
}
}
else {
if (loss > 255)
ifs = 255;
else
ifs = (int)rint(loss);
ofs = GetSignal(path.lat[y], path.lon[y]);
if (ofs < ifs && ofs != 0)
ifs = ofs;
PutSignal(path.lat[y], path.lon[y],
(unsigned char)ifs);
}
if (fd != NULL) {
if (block)
buffer_offset += sprintf(fd_buffer+buffer_offset,
" *");
fprintf(fd, "%s\n", fd_buffer);
}
/* Mark this point as having been analyzed */
PutMask(path.lat[y], path.lon[y],
(GetMask(path.lat[y], path.lon[y]) & 7) +
(mask_value << 3));
}
}
if(path.lat[y]>cropLat)
cropLat=path.lat[y];
if(y>cropLon)
cropLon=y;
//if(cropLon>180)
// cropLon-=360;
}
void PlotLOSMap(struct site source, double altitude, char *plo_filename,
bool use_threads)
{
/* This function performs a 360 degree sweep around the
transmitter site (source location), and plots the
line-of-sight coverage of the transmitter on the ss
generated topographic map based on a receiver located
at the specified altitude (in feet AGL). Results
are stored in memory, and written out in the form
of a topographic map when the WritePPM() function
is later invoked. */
static __thread unsigned char mask_value = 1;
FILE *fd = NULL;
if (plo_filename[0] != 0)
fd = fopen(plo_filename, "wb");
if (fd != NULL) {
fprintf(fd,
"%.3f, %.3f\t; max_west, min_west\n%.3f, %.3f\t; max_north, min_north\n",
max_west, min_west, max_north, min_north);
}
// Four sections start here
// Process north edge east/west, east edge north/south,
// south edge east/west, west edge north/south
double range_min_west[] = {min_west, min_west, min_west, max_west};
double range_min_north[] = {max_north, min_north, min_north, min_north};
double range_max_west[] = {max_west, min_west, max_west, max_west};
double range_max_north[] = {max_north, max_north, min_north, max_north};
propagationRange* r[NUM_SECTIONS];
for(int i = 0; i < NUM_SECTIONS; ++i) {
propagationRange *range = new propagationRange;
r[i] = range;
range->los = true;
range->eastwest = (range_min_west[i] == range_max_west[i] ? false : true);
range->min_west = range_min_west[i];
range->max_west = range_max_west[i];
range->min_north = range_min_north[i];
range->max_north = range_max_north[i];
range->use_threads = use_threads;
range->altitude = altitude;
range->source = source;
range->mask_value = mask_value;
range->fd = fd;
if(use_threads)
beginThread(range);
else
rangePropagation(range);
}
if(use_threads)
finishThreads();
for(int i = 0; i < NUM_SECTIONS; ++i){
delete r[i];
}
switch (mask_value) {
case 1:
mask_value = 8;
break;
case 8:
mask_value = 16;
break;
case 16:
mask_value = 32;
}
}
void PlotPropagation(struct site source, double altitude, char *plo_filename,
int propmodel, int knifeedge, int haf, int pmenv, bool
use_threads)
{
static __thread unsigned char mask_value = 1;
FILE *fd = NULL;
if (LR.erp == 0.0 && debug)
fprintf(stderr, "path loss");
else {
if (debug) {
if (dbm)
fprintf(stderr, "signal power level");
else
fprintf(stderr, "field strength");
}
}
if (debug) {
fprintf(stderr,
" contours of \"%s\"\nout to a radius of %.2f %s with Rx antenna(s) at %.2f %s AGL\n",
source.name,
metric ? max_range * KM_PER_MILE : max_range,
metric ? "kilometers" : "miles",
metric ? altitude * METERS_PER_FOOT : altitude,
metric ? "meters" : "feet");
}
if (clutter > 0.0 && debug)
fprintf(stderr, "\nand %.2f %s of ground clutter",
metric ? clutter * METERS_PER_FOOT : clutter,
metric ? "meters" : "feet");
if (plo_filename[0] != 0)
fd = fopen(plo_filename, "wb");
if (fd != NULL) {
fprintf(fd,
"%.3f, %.3f\t; max_west, min_west\n%.3f, %.3f\t; max_north, min_north\n",
max_west, min_west, max_north, min_north);
}
// Four sections start here
// Process north edge east/west, east edge north/south,
// south edge east/west, west edge north/south
double range_min_west[] = {min_west, min_west, min_west, max_west};
double range_min_north[] = {max_north, min_north, min_north, min_north};
double range_max_west[] = {max_west, min_west, max_west, max_west};
double range_max_north[] = {max_north, max_north, min_north, max_north};
propagationRange* r[NUM_SECTIONS];
for(int i = 0; i < NUM_SECTIONS; ++i) {
propagationRange *range = new propagationRange;
r[i] = range;
range->los = false;
// Only process correct half
if((NUM_SECTIONS - i) <= (NUM_SECTIONS / 2) && haf == 1)
continue;
if((NUM_SECTIONS - i) > (NUM_SECTIONS / 2) && haf == 2)
continue;
range->eastwest = (range_min_west[i] == range_max_west[i] ? false : true);
range->min_west = range_min_west[i];
range->max_west = range_max_west[i];
range->min_north = range_min_north[i];
range->max_north = range_max_north[i];
range->use_threads = use_threads;
range->altitude = altitude;
range->source = source;
range->mask_value = mask_value;
range->fd = fd;
range->propmodel = propmodel;
range->knifeedge = knifeedge;
range->pmenv = pmenv;
if(use_threads)
beginThread(range);
else
rangePropagation(range);
}
if(use_threads)
finishThreads();
for(int i = 0; i < NUM_SECTIONS; ++i){
delete r[i];
}
if (fd != NULL)
fclose(fd);
if (mask_value < 30)
mask_value++;
}
void PlotPath(struct site source, struct site destination, char mask_value)
{
/* This function analyzes the path between the source and
destination locations. It determines which points along
the path have line-of-sight visibility to the source.
Points along with path having line-of-sight visibility
to the source at an AGL altitude equal to that of the
destination location are stored by setting bit 1 in the
mask[][] array, which are displayed in green when PPM
maps are later generated by SPLAT!. */
char block;
int x, y;
register double cos_xmtr_angle, cos_test_angle, test_alt;
double distance, rx_alt, tx_alt;
ReadPath(source, destination);
for (y = 0; y < path.length; y++) {
/* Test this point only if it hasn't been already
tested and found to be free of obstructions. */
if ((GetMask(path.lat[y], path.lon[y]) & mask_value) == 0) {
distance = FEET_PER_MILE * path.distance[y];
tx_alt = earthradius + source.alt + path.elevation[0];
rx_alt =
earthradius + destination.alt + path.elevation[y];
/* Calculate the cosine of the elevation of the
transmitter as seen at the temp rx point. */
cos_xmtr_angle =
((rx_alt * rx_alt) + (distance * distance) -
(tx_alt * tx_alt)) / (2.0 * rx_alt * distance);
for (x = y, block = 0; x >= 0 && block == 0; x--) {
distance =
FEET_PER_MILE * (path.distance[y] -
path.distance[x]);
test_alt =
earthradius + (path.elevation[x] ==
0.0 ? path.
elevation[x] : path.
elevation[x] + clutter);
cos_test_angle =
((rx_alt * rx_alt) + (distance * distance) -
(test_alt * test_alt)) / (2.0 * rx_alt *
distance);
/* Compare these two angles to determine if
an obstruction exists. Since we're comparing
the cosines of these angles rather than
the angles themselves, the following "if"
statement is reversed from what it would
be if the actual angles were compared. */
if (cos_xmtr_angle >= cos_test_angle)
block = 1;
}
if (block == 0)
OrMask(path.lat[y], path.lon[y], mask_value);
}
}
}