Air density calculator: add ability to use relative humidity

Fixes #1383

src/Gui/ToolsRhoEstimator.cpp

@@ -131,6 +131,26 @@ ToolsRhoEstimator::ToolsRhoEstimator(Context *context, QWidget *parent) : QDialo
   dhl->addWidget(dewpSpinBox);
   mainVBox->addLayout(dhl);
 
+  // The relative humidity box.
+  QHBoxLayout *hhl = new QHBoxLayout;
+  rhumLabel = new QLabel(tr("Relative Humidity (%):"));
+  hhl->addWidget(rhumLabel);
+  rhumSpinBox = new QDoubleSpinBox(this);
+  rhumSpinBox->setDecimals(2);
+  rhumSpinBox->setRange(0, 100);
+  rhumSpinBox->setWrapping(false);
+  rhumSpinBox->setAlignment(Qt::AlignRight);
+  connect(rhumSpinBox, SIGNAL(valueChanged(double)),
+          this, SLOT(on_valueChanged(double)));
+  hhl->addWidget(rhumSpinBox);
+  rhumGroupBox = new QGroupBox(tr("Use Relative Humidity"));
+  rhumGroupBox->setCheckable(true);
+  rhumGroupBox->setChecked(false);
+  rhumGroupBox->setLayout(hhl);
+  connect(rhumGroupBox, SIGNAL(toggled(bool)),
+          this, SLOT(on_valueChanged()));
+  mainVBox->addWidget(rhumGroupBox);
+
   // Label for the computed air density.
   mainVBox->addSpacing(15);
   mainVBox->addWidget(new QLabel(
@@ -203,7 +223,7 @@ void ToolsRhoEstimator::on_btnOK_clicked() {
 }
 
 void ToolsRhoEstimator::on_valueChanged(double newval) {
-  newval++;  // hack to avoid the "unused parameter" g++ warning.
+  Q_UNUSED(newval)
 
   // scrape the field values, convert to metric if needed.
   double temp = tempSpinBox->value();
@@ -216,6 +236,17 @@ void ToolsRhoEstimator::on_valueChanged(double newval) {
     dewp = fahrenheit_to_celsius(dewp);
   }
 
+  if (rhumGroupBox->isChecked()) {
+    // compute dew point from relative humidity
+    dewpSpinBox->setEnabled(false);
+    dewp = dewp_from_rhum(rhumSpinBox->value(), temp);
+    dewpSpinBox->setValue(impBut->isChecked() ? celsius_to_fahrenheit(dewp) : dewp);
+  } else {
+    // compute relative humidity from dew point
+    rhumSpinBox->setValue(rhum_from_dewp(dewp, temp));
+    dewpSpinBox->setEnabled(true);
+  }
+
   // calculate rho, in (kg/m^3)
   double rho_met = calculate_rho(temp, press, dewp);
   // calculate rho in imperial units.
@@ -251,6 +282,16 @@ double ToolsRhoEstimator::rho_met_to_imp(double rho) {
   return rho * ((0.30480061 * 0.30480061 * 0.30480061) / KG_PER_LB);
 }
 
+// source: http://bmcnoldy.rsmas.miami.edu/Humidity.html
+double ToolsRhoEstimator::dewp_from_rhum(double rhum, double temp) {
+    return 243.04*(log(rhum/100)+((17.625*temp)/(243.04+temp)))/(17.625-log(rhum/100)-((17.625*temp)/(243.04+temp)));
+}
+
+// source: http://bmcnoldy.rsmas.miami.edu/Humidity.html
+double ToolsRhoEstimator::rhum_from_dewp(double dewp, double temp) {
+    return 100*(exp((17.625*dewp)/(243.04+dewp))/exp((17.625*temp)/(243.04+temp)));
+}
+
 double ToolsRhoEstimator::calculate_rho(double temp,
                                         double press,
                                         double dewp) {

src/Gui/ToolsRhoEstimator.h

@@ -25,6 +25,7 @@
 #include <QDialog>
 #include <QLineEdit>
 #include <QLabel>
+#include <QGroupBox>
 
 class Context;
 
@@ -50,18 +51,23 @@ class ToolsRhoEstimator : public QDialog {
         QLabel *tempLabel;
         QLabel *pressLabel;
         QLabel *dewpLabel;
+        QLabel *rhumLabel;
         QDoubleSpinBox *tempSpinBox;
         QDoubleSpinBox *pressSpinBox;
         QDoubleSpinBox *dewpSpinBox;
+        QDoubleSpinBox *rhumSpinBox;
+        QGroupBox *rhumGroupBox;
         double fahrenheit_to_celsius(double f);
         double celsius_to_fahrenheit(double c);
         double hectopascals_to_inchesmercury(double hpa);
         double inchesmercury_to_hectopascals(double inhg);
         double rho_met_to_imp(double rho);
+        double dewp_from_rhum(double rhum, double temp);
+        double rhum_from_dewp(double dewp, double temp);
         double calculate_rho(double temp, double press, double dewp);
 
     private slots:
         void on_radio_toggled(bool checked);
         void on_btnOK_clicked();
-        void on_valueChanged(double newval);
+        void on_valueChanged(double newval=0.0);
 };