Trim the dive to exclude surface time at beginning and end

We don't change any of the samples, we just don't plot (or consider for
dive time / mean calculations) the samples at the beginning or end of the
dive that are less than a certain threshold under water. Right now that's
an arbitrary 75cm which seems to Do The Right Thing(tm) for the dives I
tried this with - but I'm happy to look at other values if this causes
problems for people with dive computers I do not have access to.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

3 files changed, 11 insertions, 2 deletions

diff --git a/dive.c b/dive.c
index 65cfc4d53..384b8dcad 100644
--- a/dive.c
+++ b/dive.c
@@ -449,10 +449,10 @@ struct dive *fixup_dive(struct dive *dive)
 		lastindex = index;
 		lastpressure = pressure;
 
-		if (lastdepth)
+		if (lastdepth > SURFACE_THRESHOLD)
 			end = time;
 
-		if (depth) {
+		if (depth > SURFACE_THRESHOLD) {
 			if (start < 0)
 				start = lasttime;
 			if (depth > maxdepth)
@@ -479,6 +479,8 @@ struct dive *fixup_dive(struct dive *dive)
 		lastdepth = depth;
 		lasttime = time;
 	}
+	dive->start = start;
+	dive->end = end;
 	/* if all the samples for a cylinder have pressure data that
 	 * is basically equidistant throw out the sample cylinder pressure
 	 * information but make sure we still have a valid start and end
diff --git a/dive.h b/dive.h
index ff5b37a18..8a79de0b2 100644
--- a/dive.h
+++ b/dive.h
@@ -261,6 +261,7 @@ struct dive {
 	tripflag_t tripflag;
 	dive_trip_t *divetrip;
 	int selected;
+	int start, end;
 	timestamp_t when;
 	char *location;
 	char *notes;
@@ -296,6 +297,8 @@ static inline int depth_to_mbar(int depth, struct dive *dive)
 	return depth / 10.0 * specific_weight + surface_pressure + 0.5;
 }
 
+#define SURFACE_THRESHOLD 750 /* somewhat arbitrary: only below 75cm is it really diving */
+
 /* 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/profile.c b/profile.c
index 6eab3b240..065934746 100644
--- a/profile.c
+++ b/profile.c
@@ -1704,6 +1704,10 @@ static struct plot_info *create_plot_info(struct dive *dive, int nr_samples, str
 		int delay = 0;
 		struct sample *sample = dive_sample+i;
 
+		if (sample->time.seconds < dive->start || sample->time.seconds > dive->end) {
+			pi_idx--;
+			continue;
+		}
 		entry = pi->entry + i + pi_idx;
 		while (ceil_ev && ceil_ev->time.seconds <= sample->time.seconds) {
 			struct event *next_ceil_ev = get_next_event(ceil_ev->next, "ceiling");