X-Git-Url: https://git.mxchange.org/?a=blobdiff_plain;f=src%2FEnvironment%2Fatmosphere.cxx;h=022ea540ec65a9045eadd131438bde3a87785b76;hb=a1031b052dd40ca3a4ea68dcd7f572b7d9e4bb24;hp=a15c943ed47aba514bddb6212459f38f9a85c3fc;hpb=a6db6d89ff41a619569e6433409e8bf62ff98499;p=flightgear.git

diff --git a/src/Environment/atmosphere.cxx b/src/Environment/atmosphere.cxx
index a15c943ed..022ea540e 100644
--- a/src/Environment/atmosphere.cxx
+++ b/src/Environment/atmosphere.cxx
@@ -108,7 +108,7 @@ pair<double,double> PT_vs_hpt(
   }
   
 // Should never get here.
-  SG_LOG(SG_GENERAL, SG_ALERT, "PT_vs_hpt: ran out of layers");
+  SG_LOG(SG_ENVIRONMENT, SG_ALERT, "PT_vs_hpt: ran out of layers for h=" << hh );
   return make_pair(d0, d0);
 }
 
@@ -250,7 +250,7 @@ double FGAtmo::QNH(const double field_elev, const double field_press) {
     double rslt =  field_press
             * pow(1. + ISA::lam0 * field_elev / ISA::T0 * prat, 1./nn);
 #if 0
-    SG_LOG(SG_GENERAL, SG_ALERT, "QNH: elev: " << field_elev
+    SG_LOG(SG_ENVIRONMENT, SG_ALERT, "QNH: elev: " << field_elev
                 << "  press: " << field_press
                 << "  prat: "  << prat
                 << "  rslt: " << rslt
@@ -260,6 +260,21 @@ double FGAtmo::QNH(const double field_elev, const double field_press) {
     return rslt;
 }
 
+// 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) {
     using namespace atmodel;
     const int bs(200);