Merge branch 'pressure'

Make depth to absolute pressure conversions consistent.

3 files changed, 33 insertions, 17 deletions

diff --git a/dive.h b/dive.h
index a2d14215b..ff5b37a18 100644
--- a/dive.h
+++ b/dive.h
@@ -282,6 +282,20 @@ struct dive {
 	struct sample sample[];
 };
 
+/* Pa = N/m^2 - so we determine the weight (in N) of the mass of 10m
+ * of water (and use standard salt water at 1.03kg per liter if we don't know salinity)
+ * and add that to the surface pressure (or to 1013 if that's unknown) */
+static inline int depth_to_mbar(int depth, struct dive *dive)
+{
+	double specific_weight = 1.03 * 0.981;
+	int surface_pressure = 1013;
+	if (dive->salinity)
+		specific_weight = dive->salinity / 10000.0 * 0.981;
+	if (dive->surface_pressure.mbar)
+		surface_pressure = dive->surface_pressure.mbar;
+	return depth / 10.0 * specific_weight + surface_pressure + 0.5;
+}
+
 /* this is a global spot for a temporary dive structure that we use to
  * be able to edit a dive without unintended side effects */
 extern struct dive edit_dive;
diff --git a/divelist.c b/divelist.c
index 056a4f64a..6aa26c2bd 100644
--- a/divelist.c
+++ b/divelist.c
@@ -711,7 +711,7 @@ static int calculate_otu(struct dive *dive)
 		int o2 = dive->cylinder[sample->cylinderindex].gasmix.o2.permille;
 		if (!o2)
 			o2 = AIR_PERMILLE;
-		po2 = o2 / 1000.0 * (sample->depth.mm + 10000) / 10000.0;
+		po2 = o2 / 1000.0 * depth_to_mbar(sample->depth.mm, dive) / 1000.0;
 		if (po2 >= 0.5)
 			otu += pow(po2 - 0.5, 0.83) * t / 30.0;
 	}
@@ -771,8 +771,8 @@ static int calculate_sac(struct dive *dive)
 			}
 		}
 	}
-	/* Mean pressure in atm: 1 atm per 10m */
-	pressure = 1 + (dive->meandepth.mm / 10000.0);
+	/* Mean pressure in bar (SAC calculations are in bar*l/min) */
+	pressure = depth_to_mbar(dive->meandepth.mm, dive) / 1000.0;
 	sac = airuse / pressure * 60 / duration;
 
 	/* milliliters per minute.. */
diff --git a/profile.c b/profile.c
index 73dbc6648..6eab3b240 100644
--- a/profile.c
+++ b/profile.c
@@ -1179,8 +1179,7 @@ static void set_sac_color(struct graphics_context *gc, int sac, int avg_sac)
 	((GET_PRESSURE((_entry1)) - GET_PRESSURE((_entry2))) *			\
 		(_dive)->cylinder[(_entry1)->cylinderindex].type.size.mliter /	\
 		(((_entry2)->sec - (_entry1)->sec) / 60.0) /			\
-		(1 + ((_entry1)->depth + (_entry2)->depth) / 20000.0) /		\
-		1000.0)
+		depth_to_mbar(((_entry1)->depth + (_entry2)->depth) / 2.0, (_dive)))
 
 #define SAC_WINDOW 45	/* sliding window in seconds for current SAC calculation */
 
@@ -1671,6 +1670,7 @@ static struct plot_info *create_plot_info(struct dive *dive, int nr_samples, str
 	gboolean missing_pr = FALSE;
 	struct plot_data *entry = NULL;
 	struct event *ev, *ceil_ev;
+	double amb_pressure;
 
 	/* we want to potentially add synthetic plot_info elements for the gas changes */
 	nr = nr_samples + 4 + 2 * count_gas_change_events(dive);
@@ -1780,7 +1780,6 @@ static struct plot_info *create_plot_info(struct dive *dive, int nr_samples, str
 	current = track_pr[pi->entry[2].cylinderindex];
 	for (i = 0; i < nr + 1; i++) {
 		int fo2, fhe;
-		double pressure;
 
 		entry = pi->entry + i + 1;
 
@@ -1804,19 +1803,19 @@ static struct plot_info *create_plot_info(struct dive *dive, int nr_samples, str
 					list_add(track_pr[cylinderindex], current);
 			}
 		}
-		pressure = (entry->depth + 10000) / 10000.0 * 1.01325;
+		amb_pressure = depth_to_mbar(entry->depth, dive) / 1000.0;
 		fo2 = dive->cylinder[cylinderindex].gasmix.o2.permille;
 		fhe = dive->cylinder[cylinderindex].gasmix.he.permille;
 
 		if (!fo2)
 			fo2 = AIR_PERMILLE;
-		entry->po2 = fo2 / 1000.0 * pressure;
-		entry->phe = fhe / 1000.0 * pressure;
-		entry->pn2 = (1000 - fo2 - fhe) / 1000.0 * pressure;
+		entry->po2 = fo2 / 1000.0 * amb_pressure;
+		entry->phe = fhe / 1000.0 * amb_pressure;
+		entry->pn2 = (1000 - fo2 - fhe) / 1000.0 * amb_pressure;
 
 		/* finally, do the discrete integration to get the SAC rate equivalent */
 		current->pressure_time += (entry->sec - (entry-1)->sec) *
-			(1 + (entry->depth + (entry-1)->depth) / 20000.0);
+			depth_to_mbar((entry->depth + (entry-1)->depth) / 2, dive) / 1000.0;
 		missing_pr |= !SENSOR_PRESSURE(entry);
 	}
 
@@ -1837,8 +1836,9 @@ static struct plot_info *create_plot_info(struct dive *dive, int nr_samples, str
 	pi->entry[i].same_cylinder = 1;
 	pi->entry[i].cylinderindex = pi->entry[i-1].cylinderindex;
 	INTERPOLATED_PRESSURE(pi->entry + i) = GET_PRESSURE(pi->entry + i - 1);
-	pi->entry[i].po2 = pi->entry[i-1].po2 / (pi->entry[i].depth + 10000.0) * 10000.0;
-	pi->entry[i].phe = pi->entry[i-1].phe / (pi->entry[i].depth + 10000.0) * 10000.0;
+	amb_pressure = depth_to_mbar(pi->entry[i - 1].depth, dive) / 1000.0;
+	pi->entry[i].po2 = pi->entry[i-1].po2 / amb_pressure;
+	pi->entry[i].phe = pi->entry[i-1].phe / amb_pressure;
 	pi->entry[i].pn2 = 1.01325 - pi->entry[i].po2 - pi->entry[i].phe;
 	pi->entry[i+1].sec = sec + 40;
 	pi->entry[i+1].same_cylinder = 1;
@@ -1848,15 +1848,17 @@ static struct plot_info *create_plot_info(struct dive *dive, int nr_samples, str
 	pi->entry[i+1].phe = pi->entry[i].phe;
 	pi->entry[i+1].pn2 = pi->entry[i].pn2;
 	/* make sure the first two pi entries have a sane po2 / phe / pn2 */
+	amb_pressure = depth_to_mbar(pi->entry[2].depth, dive) / 1000.0;
 	if (pi->entry[1].po2 < 0.01)
-		pi->entry[1].po2 = pi->entry[2].po2 / (pi->entry[2].depth + 10000.0) * 10000.0;
+		pi->entry[1].po2 = pi->entry[2].po2 / amb_pressure;
 	if (pi->entry[1].phe < 0.01)
-		pi->entry[1].phe = pi->entry[2].phe / (pi->entry[2].depth + 10000.0) * 10000.0;
+		pi->entry[1].phe = pi->entry[2].phe / amb_pressure;
 	pi->entry[1].pn2 = 1.01325 - pi->entry[1].po2 - pi->entry[1].phe;
+	amb_pressure = depth_to_mbar(pi->entry[1].depth, dive) / 1000.0;
 	if (pi->entry[0].po2 < 0.01)
-		pi->entry[0].po2 = pi->entry[1].po2 / (pi->entry[1].depth + 10000.0) * 10000.0;
+		pi->entry[0].po2 = pi->entry[1].po2 / amb_pressure;
 	if (pi->entry[0].phe < 0.01)
-		pi->entry[0].phe = pi->entry[1].phe / (pi->entry[1].depth + 10000.0) * 10000.0;
+		pi->entry[0].phe = pi->entry[1].phe / amb_pressure;
 	pi->entry[0].pn2 = 1.01325 - pi->entry[0].po2 - pi->entry[0].phe;
 
 	/* the number of actual entries - some computers have lots of