/* compute boat speed from given power level, true wind angle and true wind speed */
double BoatPlan::Speed(double W, double VW)
{
W = positive_degrees(W);
if(VW < 0 || VW > MAX_KNOTS)
return NAN;
double W1 = floor(W/DEGREE_STEP)*DEGREE_STEP;
double W2 = ceil(W/DEGREE_STEP)*DEGREE_STEP;
/* get headings nearby each other */
while(W1 - W2 > 180)
W2 += 360;
while(W2 - W1 > 180)
W1 += 360;
int W1i = positive_degrees(W1)/DEGREE_STEP;
int W2i = positive_degrees(W2)/DEGREE_STEP;
int VW1i = ClosestVWi(VW), VW2i = VW1i+1;
double VW1 = wind_speeds[VW1i], VW2 = wind_speeds[VW2i];
double VB11 = speed[VW1i][W1i].VB;
double VB12 = speed[VW1i][W2i].VB;
double VB21 = speed[VW2i][W1i].VB;
double VB22 = speed[VW2i][W2i].VB;
double VB1 = interp_value(VW, VW1, VW2, VB11, VB21);
double VB2 = interp_value(VW, VW1, VW2, VB12, VB22);
double VB = interp_value(W, W1, W2, VB1, VB2);
return VB;
}
SailingVMG BoatPlan::GetVMGTrueWind(double VW)
{
int VW1i, VW2i;
ClosestVWi(VW, VW1i, VW2i);
SailingWindSpeed &ws1 = wind_speeds[VW1i], &ws2 = wind_speeds[VW2i];
double VW1 = ws1.VW, VW2 = ws2.VW;
SailingVMG vmg, vmg1 = ws1.VMG, vmg2 = ws2.VMG;
for(int i=0; i<4; i++)
vmg.values[i] = interp_value(VW, VW1, VW2, vmg1.values[i], vmg2.values[i]);
return vmg;
}
/* compute boat speed from true wind angle and true wind speed
*/
double Polar::Speed(double W, double VW, bool bound)
{
if(VW < 0)
return NAN;
if(!degree_steps.size() || !wind_speeds.size())
return NAN;
W = positive_degrees(W);
// assume symmetric
if(W > 180)
W = 360 - W;
if(W < degree_steps[0] || W > degree_steps[degree_steps.size()-1])
return NAN;
if(bound)
if(VW < wind_speeds[0].VW || VW > wind_speeds[wind_speeds.size()-1].VW)
return NAN;
unsigned int W1i = degree_step_index[(int)floor(W)];
unsigned int W2i = degree_steps.size() == 1 ? 0 : W1i+1;
double W1 = degree_steps[W1i], W2 = degree_steps[W2i];
int VW1i, VW2i;
ClosestVWi(VW, VW1i, VW2i);
if(VW1i == (int)wind_speeds.size() - 1)
VW2i = VW1i;
else
VW2i = VW1i + 1;
SailingWindSpeed &ws1 = wind_speeds[VW1i], &ws2 = wind_speeds[VW2i];
double VW1 = ws1.VW, VW2 = ws2.VW;
double VB11 = ws1.speeds[W1i], VB12 = ws1.speeds[W2i];
double VB21 = ws2.speeds[W1i], VB22 = ws2.speeds[W2i];
double VB1 = interp_value(VW, VW1, VW2, VB11, VB21);
double VB2 = interp_value(VW, VW1, VW2, VB12, VB22);
double VB = interp_value(W, W1, W2, VB1, VB2);
if(VB < 0) // with faulty polars, extrapolation, sometimes results in negative boat speed
return 0;
return VB;
}
SailingVMG BoatPlan::GetVMG(double VW)
{
int VW2i = ClosestVWi(VW), VW1i = VW2i > 0 ? VW2i - 1 : 0;
SailingVMG vmg, vmg1 = VMG[VW1i], vmg2 = VMG[VW2i];
double VW1 = wind_speeds[VW1i], VW2 = wind_speeds[VW2i];
vmg.PortTackUpWind = DEGREE_STEP * interp_value
(VW, VW1, VW2, vmg1.PortTackUpWind, vmg2.PortTackUpWind);
vmg.StarboardTackUpWind = DEGREE_STEP * interp_value
(VW, VW1, VW2, vmg1.StarboardTackUpWind, vmg2.StarboardTackUpWind);
vmg.PortTackDownWind = DEGREE_STEP * interp_value
(VW, VW1, VW2, vmg1.PortTackDownWind, vmg2.PortTackDownWind);
vmg.StarboardTackDownWind = DEGREE_STEP * interp_value
(VW, VW1, VW2, vmg1.StarboardTackDownWind, vmg2.StarboardTackDownWind);
return vmg;
}
/* compute boat speed from true wind angle and true wind speed
Maybe this should use rectangular coordinate interpolation when the speed
is outside the VMG zone.
*/
double BoatPlan::Speed(double W, double VW)
{
if(VW < 0)
return NAN;
W = positive_degrees(W);
unsigned int W1i = degree_step_index[(int)floor(W)], W2i;
double W1 = degree_steps[W1i], W2;
if(W1i == degree_steps.size()-1) {
W2i = 0;
W2 = 360 + degree_steps[0];
} else {
W2i = W1i+1;
W2 = degree_steps[W2i];
}
int VW1i, VW2i;
ClosestVWi(VW, VW1i, VW2i);
if(VW1i == wind_speeds.size() - 1)
VW2i = VW1i;
else
VW2i = VW1i + 1;
SailingWindSpeed &ws1 = wind_speeds[VW1i], &ws2 = wind_speeds[VW2i];
double VW1 = ws1.VW, VW2 = ws2.VW;
double VB11 = ws1.speeds[W1i].VB, VB12 = ws1.speeds[W2i].VB;
double VB21 = ws2.speeds[W1i].VB, VB22 = ws2.speeds[W2i].VB;
double VB1 = interp_value(VW, VW1, VW2, VB11, VB21);
double VB2 = interp_value(VW, VW1, VW2, VB12, VB22);
double VB = interp_value(W, W1, W2, VB1, VB2);
if(VB < 0) // with faulty polars, extrapolation, sometimes results in negative boat speed
return 0;
return VB;
}
/* eta is a measure of efficiency of the boat, from .01 for racing boats to .5 for
heavy cruisers */
void BoatPlan::ComputeBoatSpeeds(Boat &boat, PolarMethod method, int speed)
{
// fileFileName = _T("");
if(/*polarmethod == FROM_FILE ||*/
wind_speeds.size() != num_computed_wind_speeds ||
degree_steps.size() != computed_degree_count) {
wind_speeds.clear();
degree_steps.clear();
for(unsigned int Wi = 0; Wi < computed_degree_count; Wi++)
degree_steps.push_back(computed_degree_step*Wi);
UpdateDegreeStepLookup();
for(unsigned int VWi = 0; VWi < num_computed_wind_speeds; VWi++) {
wind_speeds.push_back(SailingWindSpeed(computed_wind_speeds[VWi]));
wind_speeds[VWi].speeds.clear();
for(unsigned int Wi = 0; Wi < computed_degree_count; Wi++)
wind_speeds[VWi].speeds.push_back(SailingWindSpeed::SailingSpeed(0, degree_steps[Wi]));
}
}
// for IMF computation
double SADR = boat.SailAreaDisplacementRatio();
double lwl_ft = boat.lwl_ft;
double hull_speed = boat.HullSpeed();
int VW1i, VW2i;
if(speed == -1) // all speeds
VW1i = 0, VW2i = wind_speeds.size() - 1;
else
ClosestVWi(speed, VW1i, VW2i);
for(int VWi = VW1i; VWi <= VW2i; VWi++) {
for(unsigned int Wi = 0; Wi <= computed_degree_count/2; Wi++) {
double VW = wind_speeds[VWi].VW;
double W = Wi * computed_degree_step;
double B, VB, A, VA;
switch(method) {
case TRANSFORM:
BoatSteadyState(deg2rad(W), VW, B, VB, A, VA, boat);
break;
case IMF:
{
if(fabsf(W) < 30)
VB = 0;
else {
double base_speed = 2.62 + .066*SADR + .051*lwl_ft;
double b = 1 / sqrt(VW + 3);
VB = base_speed*(sin(deg2rad(W)/2) + b*cos(deg2rad(W))) * sqrt(20*VW) / 8;
if(VB > hull_speed)
VB = hull_speed;
}
}
default:
printf("BoatPlan::ComputeBoatSpeeds called with invalid method: %d\n", method);
return;
}
Set(Wi, VWi, VB, W);
if(W != 0) // assume symmetric performance
Set(computed_degree_count-Wi, VWi, VB, DEGREES-W);
}
CalculateVMG(VWi);
}
polarmethod = method;
}
