+#include <boost/tuple/tuple.hpp>
+
#include <simgear/math/SGMath.hxx>
+#include <simgear/debug/logstream.hxx>
#include "atmosphere.hxx"
using namespace std;
#include <iostream>
+#include <cstdio>
+
+const ISA_layer ISA_def[] = {
+// 0 1 2 3 4 5 6 7 8
+// id (m) (ft) (Pa) (inHg) (K) (C) (K/m) (K/ft)
+ISA_layer(0, 0, 0, 101325, 29.92126, 288.15, 15.00, 0.0065, 0.0019812),
+ISA_layer(1, 11000, 36089, 22632.1, 6.683246, 216.65, -56.50, 0, 0),
+ISA_layer(2, 20000, 65616, 5474.89, 1.616734, 216.65, -56.50, -0.0010, -0.0003048),
+ISA_layer(3, 32000, 104986, 868.019, 0.256326, 228.65, -44.50, -0.0028, -0.0008534),
+ISA_layer(4, 47000, 154199, 110.906, 0.0327506, 270.65, -2.50, 0, 0),
+ISA_layer(5, 51000, 167322, 66.9389, 0.0197670, 270.65, -2.50, 0.0028, 0.0008534),
+ISA_layer(6, 71000, 232939, 3.95642, 0.00116833, 214.65, -58.50, 0.0020, 0.0006096),
+ISA_layer(7, 80000, 262467, 0.88628, 0.000261718, 196.65, -76.50),
+};
+
+const int ISA_def_size(sizeof(ISA_def) / sizeof(ISA_layer));
+
+// Pressure within a layer, as a function of height.
+// Physics model: standard or nonstandard atmosphere,
+// depending on what parameters you pass in.
+// Height in meters, pressures in pascals.
+// As always, lapse is positive in the troposphere,
+// and zero in the first part of the stratosphere.
+
+double P_layer(const double height, const double href,
+ const double Pref, const double Tref,
+ const double lapse) {
+ using namespace atmodel;
+ if (lapse) {
+ double N = lapse * Rgas / mm / g;
+ return Pref * pow( (Tref - lapse*(height - href)) / Tref , (1/N));
+ } else {
+ return Pref * exp(-g * mm / Rgas / Tref * (height - href));
+ }
+}
+
+
+// Temperature within a layer, as a function of height.
+// Physics model: standard or nonstandard atmosphere
+// depending on what parameters you pass in.
+// $hh in meters, pressures in Pa.
+// As always, $lambda is positive in the troposphere,
+// and zero in the first part of the stratosphere.
+double T_layer (
+ const double hh,
+ const double hb,
+ const double Pb,
+ const double Tb,
+ const double lambda) {
+ return Tb - lambda*(hh - hb);
+}
+
+// Pressure and temperature as a function of height, Psl, and Tsl.
+// heights in meters, pressures in Pa.
+// Daisy chain version.
+// We need "seed" values for sea-level pressure and temperature.
+// In addition, for every layer, we need three things
+// from the table: the reference height in that layer,
+// the lapse in that layer, and the cap (if any) for that layer
+// (which we take from the /next/ row of the table, if any).
+pair<double,double> PT_vs_hpt(
+ const double hh,
+ const double _p0,
+ const double _t0
+) {
+
+ const double d0(0);
+ double hgt = ISA_def[0].height;
+ double p0 = _p0;
+ double t0 = _t0;
+#if 0
+ cout << "PT_vs_hpt: " << hh << " " << p0 << " " << t0 << endl;
+#endif
+
+ int ii = 0;
+ for (const ISA_layer* pp = ISA_def; pp->lapse != -1; pp++, ii++) {
+#if 0
+ cout << "PT_vs_hpt: " << ii
+ << " height: " << pp->height
+ << " temp: " << pp->temp
+ << " lapse: " << pp->lapse
+ << endl;
+#endif
+ double xhgt(9e99);
+ double lapse = pp->lapse;
+// Stratosphere starts at a definite temperature,
+// not a definite height:
+ if (ii == 0) {
+ xhgt = hgt + (t0 - (pp+1)->temp) / lapse;
+ } else if ((pp+1)->lapse != -1) {
+ xhgt = (pp+1)->height;
+ }
+ if (hh <= xhgt) {
+ return make_pair(P_layer(hh, hgt, p0, t0, lapse),
+ T_layer(hh, hgt, p0, t0, lapse));
+ }
+ p0 = P_layer(xhgt, hgt, p0, t0, lapse);
+ t0 = t0 - lapse * (xhgt - hgt);
+ hgt = xhgt;
+ }
+
+// Should never get here.
+ SG_LOG(SG_ENVIRONMENT, SG_ALERT, "PT_vs_hpt: ran out of layers for h=" << hh );
+ return make_pair(d0, d0);
+}
+
FGAtmoCache::FGAtmoCache() :
a_tvs_p(0)
delete a_tvs_p;
}
-// Pressure as a function of height.
-// Valid below 32000 meters,
-// i.e. troposphere and first two layers of stratosphere.
-// Does not depend on any caching; can be used to
-// *construct* caches and interpolation tables.
-//
-// Height in meters, pressure in pascals.
-
-double FGAtmo::p_vs_a(const double height) {
- using namespace atmodel;
- if (height <= 11000.) {
- return P_layer(height, 0.0, ISA::P0, ISA::T0, ISA::lam0);
- } else if (height <= 20000.) {
- return P_layer(height, 11000., 22632.06, 216.65, 0.0);
- } else if (height <= 32000.) {
- return P_layer(height, 20000., 5474.89, 216.65, -0.001);
- }
- return 0;
-}
+/////////////
+// The following two routines are called "fake" because they
+// bypass the exceedingly complicated layer model implied by
+// the "weather conditioins" popup menu.
+// For now we must bypass it for several reasons, including
+// the fact that we don't have an "environment" object for
+// the airport (only for the airplane).
// degrees C, height in feet
-double FGAtmo::fake_t_vs_a_us(const double h_ft) {
+double FGAtmo::fake_T_vs_a_us(const double h_ft,
+ const double Tsl) const {
using namespace atmodel;
- return ISA::T0 - ISA::lam0 * h_ft * foot - freezing;
+ return Tsl - ISA::lam0 * h_ft * foot;
}
// Dewpoint. degrees C or K, height in feet
a_tvs_p = new SGInterpTable;
for (double hgt = -1000; hgt <= 32000;) {
- double press = p_vs_a(hgt);
+ double press,temp;
+ boost::tie(press, temp) = PT_vs_hpt(hgt);
a_tvs_p->addEntry(press / inHg, hgt / foot);
#ifdef DEBUG_EXPORT_P_H
tabulate();
}
-// Pressure within a layer, as a function of height.
-// Physics model: standard or nonstandard atmosphere,
-// depending on what parameters you pass in.
-// Height in meters, pressures in pascals.
-// As always, lapse is positive in the troposphere,
-// and zero in the first part of the stratosphere.
-
-double FGAtmo::P_layer(const double height, const double href,
- const double Pref, const double Tref,
- const double lapse) {
- using namespace atmodel;
- if (lapse) {
- double N = lapse * Rgas / mm / g;
- return Pref * pow( (Tref - lapse*(height - href)) / Tref , (1/N));
- } else {
- return Pref * exp(-g * mm / Rgas / Tref * (height - href));
- }
-}
-
// Check the basic function,
// then compare against the interpolator.
void FGAtmoCache::check_model() {
break;
using namespace atmodel;
cache();
- double press = p_vs_a(height);
+ double press,temp;
+ boost::tie(press, temp) = PT_vs_hpt(height);
cout << "Height: " << height
<< " \tpressure: " << press << endl;
cout << "Check: "
//////////////////////////////////////////////////////////////////////
-FGAltimeter::FGAltimeter() : kset(atmodel::ISA::P0), kft(0)
+FGAltimeter::FGAltimeter()
{
cache();
}
return (press_alt - kollsman_shift);
}
-// Altimeter setting.
-// Field elevation in feet
-// Field pressure in inHg
-// field elevation in troposphere only
-double FGAtmo::qnh(const double field_ft, const double press_inHg) {
+// Altimeter setting _in pascals_
+// ... caller gets to convert to inHg or millibars
+// Field elevation in m
+// Field pressure in pascals
+// Valid for fields within the troposphere only.
+double FGAtmo::QNH(const double field_elev, const double field_press) {
using namespace atmodel;
// Equation derived in altimetry.htm
// exponent in QNH equation:
double nn = ISA::lam0 * Rgas / g / mm;
// pressure ratio factor:
- double prat = pow(ISA::P0/inHg / press_inHg, nn);
+ double prat = pow(ISA::P0 / field_press, nn);
+ double rslt = field_press
+ * pow(1. + ISA::lam0 * field_elev / ISA::T0 * prat, 1./nn);
+#if 0
+ SG_LOG(SG_ENVIRONMENT, SG_ALERT, "QNH: elev: " << field_elev
+ << " press: " << field_press
+ << " prat: " << prat
+ << " rslt: " << rslt
+ << " inHg: " << inHg
+ << " rslt/inHG: " << rslt/inHg);
+#endif
+ return rslt;
+}
- return press_inHg
- * pow(1 + ISA::lam0 * field_ft * foot / ISA::T0 * prat, 1/nn);
+// Invert the QNH calculation to get the field pressure from a metar
+// report.
+// field pressure _in pascals_
+// ... caller gets to convert to inHg or millibars
+// Field elevation in m
+// Altimeter setting (QNH) in pascals
+// Valid for fields within the troposphere only.
+double FGAtmo::fieldPressure(const double field_elev, const double qnh)
+{
+ using namespace atmodel;
+ static const double nn = ISA::lam0 * Rgas / g / mm;
+ const double pratio = pow(qnh / ISA::P0, nn);
+ return ISA::P0 * pow(pratio - field_elev * ISA::lam0 / ISA::T0, 1.0 / nn);
}
void FGAltimeter::dump_stack1(const double Tref) {
double hgts[] = {0, 2500, 5000, 7500, 10000, -9e99};
for (int ii = 0; ; ii++) {
double hgt_ft = hgts[ii];
+ double hgt = hgt_ft * foot;
if (hgt_ft < -1e6)
break;
- double press = P_layer(hgt_ft*foot, 0, ISA::P0, Tref, ISA::lam0);
- double p_inHg = press / inHg;
- double qnhx = qnh(hgt_ft, p_inHg);
+ double press = P_layer(hgt, 0, ISA::P0, Tref, ISA::lam0);
+ double qnhx = QNH(hgt, press) / inHg;
double qnh2 = SGMiscd::round(qnhx*100)/100;
+ double p_inHg = press / inHg;
double Aprind = reading_ft(p_inHg);
double Apr = a_vs_p(p_inHg*inHg) / foot;
double hind = reading_ft(p_inHg, qnh2);
projects / flightgear.git / blobdiff