Store timestamp for each value in timeseries

This fixes a bug that caused the time values in the plots drift away with
increasing device uptime.

include/timeseries.h

@@ -4,16 +4,19 @@
 
 #include <deque>
 
+typedef std::pair<uint64_t, float> timeseries_entry_t;
+typedef std::deque< timeseries_entry_t > timeseries_data_t;
+
 typedef struct {
-    uint64_t tstart, tend, interval;
-    std::deque<float> data;
+    uint64_t tstart, tend;
+    timeseries_data_t data;
     const char *unit;
     const char *format;
 } timeseries_t;
 
-void timeseries_init(timeseries_t *ts, uint64_t tstart, uint64_t interval, const char *unit, const char *format);
+void timeseries_init(timeseries_t *ts, uint64_t tstart, const char *unit, const char *format);
 
-void timeseries_append(timeseries_t *ts, float value);
+void timeseries_append(timeseries_t *ts, uint64_t timestamp, float value);
 
 // remove oldest values
-void timeseries_prune(timeseries_t *ts, float duration);
+void timeseries_prune(timeseries_t *ts, uint64_t duration);

src/epaper.cpp

@@ -64,7 +64,7 @@ void epaper_draw_and_hibernate(epaper_callback cb, bool full_refresh)
 }
 
 // find minimum and maximum values in a vector. NaN is ignored.
-	template<typename T>
+template<typename T>
 void minmax(const std::deque<T> &vec, T *min, T *max)
 {
 	bool first = true;
@@ -94,12 +94,42 @@ void minmax(const std::deque<T> &vec, T *min, T *max)
 	}
 }
 
+void minmax(const timeseries_data_t &ts, float *min, float *max)
+{
+	bool first = true;
+
+	// fallback values: will be used if the vector is empty or only consists of NaNs
+	*min = 0;
+	*max = 1;
+
+	for(auto &p: ts) {
+		float v = p.second;
+		if(isnan(v)) {
+			continue;
+		}
+
+		if(first) {
+			*min = *max = v;
+			first = false;
+			continue;
+		}
+
+		if(v < *min) {
+			*min = v;
+		}
+
+		if(v > *max) {
+			*max = v;
+		}
+	}
+}
+
 void epaper_plot(uint16_t x, uint16_t y, uint16_t w, uint16_t h, timeseries_t *timeseries, uint32_t time_tick_interval)
 {
 	char s[32];
 
 	uint32_t trange = timeseries->tend - timeseries->tstart;
-	uint32_t tstep = timeseries->interval;
+	uint32_t tstep = trange / timeseries->data.size();
 
 	if(trange == 0) {
 		trange = 3600;
@@ -216,17 +246,10 @@ void epaper_plot(uint16_t x, uint16_t y, uint16_t w, uint16_t h, timeseries_t *t
 	}
 
 	size_t i = 0;
-	for(uint32_t reltime = 0; reltime < trange; reltime += tstep) {
-		if(i >= timeseries->data.size()) {
-			Serial.println(F("Index out of range! Time range does not match data points."));
-			break;
-		}
+	for(auto &p: timeseries->data) {
+		uint32_t reltime = p.first - timeseries->tstart;
 
-		/*Serial.print(F("Processing data point at dt="));
-			Serial.print(reltime);
-			Serial.print(F("… "));*/
-
-		float val = timeseries->data[i++];
+		float val = timeseries->data[i++].second;
 		if(isnan(val)) {
 			//Serial.println(F("Skipping NaN!"));
 

src/main.cpp

@@ -99,14 +99,14 @@ void wifi_setup(void)
 
 void initSCD30(void)
 {
-	timeseries_init(&ts_scd30_co2, timeClient.getEpochTime(), 15, "ppm", "%.0f");
-	timeseries_init(&ts_scd30_temperature, timeClient.getEpochTime(), 15, "°C", "%.1f");
-	timeseries_init(&ts_scd30_humidity, timeClient.getEpochTime(), 15, "%", "%.1f");
-	timeseries_init(&ts_bme680_temperature, timeClient.getEpochTime(), 15, "°C", "%.1f");
-	timeseries_init(&ts_bme680_humidity, timeClient.getEpochTime(), 15, "%", "%.1f");
-	timeseries_init(&ts_bme680_pressure, timeClient.getEpochTime(), 15, "hPa", "%.2f");
-	timeseries_init(&ts_bme680_gas_resistance, timeClient.getEpochTime(), 15, "kOhm", "%.1f");
-	timeseries_init(&ts_bme680_db, timeClient.getEpochTime(), 15, "dB", "%.2f");
+	timeseries_init(&ts_scd30_co2,             timeClient.getEpochTime(), "ppm",  "%.0f");
+	timeseries_init(&ts_scd30_temperature,     timeClient.getEpochTime(), "°C",   "%.1f");
+	timeseries_init(&ts_scd30_humidity,        timeClient.getEpochTime(), "%",    "%.1f");
+	timeseries_init(&ts_bme680_temperature,    timeClient.getEpochTime(), "°C",   "%.1f");
+	timeseries_init(&ts_bme680_humidity,       timeClient.getEpochTime(), "%",    "%.1f");
+	timeseries_init(&ts_bme680_pressure,       timeClient.getEpochTime(), "hPa",  "%.2f");
+	timeseries_init(&ts_bme680_gas_resistance, timeClient.getEpochTime(), "kOhm", "%.1f");
+	timeseries_init(&ts_bme680_db,             timeClient.getEpochTime(), "dB",   "%.2f");
 
 	// Try to initialize!
 	if (!scd30.begin()) {
@@ -433,9 +433,10 @@ void loop(void)
 
 		// skip the first readout because the CO2 reading is then invalid
 		if(!first_scd30_readout) {
-			timeseries_append(&ts_scd30_co2, scd30.CO2);
-			timeseries_append(&ts_scd30_temperature, scd30.temperature);
-			timeseries_append(&ts_scd30_humidity, scd30.relative_humidity);
+			uint64_t updatetime = timeClient.getEpochTime();
+			timeseries_append(&ts_scd30_co2, updatetime, scd30.CO2);
+			timeseries_append(&ts_scd30_temperature, updatetime, scd30.temperature);
+			timeseries_append(&ts_scd30_humidity, updatetime, scd30.relative_humidity);
 		} else {
 			first_scd30_readout = false;
 		}
@@ -444,10 +445,11 @@ void loop(void)
 		// milliseconds), but the SCD30 is running autonomously, so this does not
 		// disturb that measurement.
 		if(bme680.performReading()) {
-			timeseries_append(&ts_bme680_temperature, bme680.temperature);
-			timeseries_append(&ts_bme680_humidity, bme680.humidity);
-			timeseries_append(&ts_bme680_pressure, bme680.pressure / 100.0);
-			timeseries_append(&ts_bme680_gas_resistance, bme680.gas_resistance / 1000.0);
+			uint64_t updatetime = timeClient.getEpochTime();
+			timeseries_append(&ts_bme680_temperature, updatetime, bme680.temperature);
+			timeseries_append(&ts_bme680_humidity, updatetime, bme680.humidity);
+			timeseries_append(&ts_bme680_pressure, updatetime, bme680.pressure / 100.0);
+			timeseries_append(&ts_bme680_gas_resistance, updatetime, bme680.gas_resistance / 1000.0);
 
 			bme680_max_resistance *= BME680_MAX_ADAPTATION_FACTOR;
 			if(bme680.gas_resistance > bme680_max_resistance) {
@@ -455,7 +457,7 @@ void loop(void)
 			}
 
 			bme680_db = 10 * log10(bme680.gas_resistance / bme680_max_resistance);
-			timeseries_append(&ts_bme680_db, bme680_db);
+			timeseries_append(&ts_bme680_db, updatetime, bme680_db);
 
 			Serial.println("BME680:");
 			Serial.print("Temperature: ");

src/timeseries.cpp

@@ -1,32 +1,39 @@
 #include "timeseries.h"
 
 
-void timeseries_init(timeseries_t *ts, uint64_t tstart, uint64_t interval, const char *unit, const char *format)
+void timeseries_init(timeseries_t *ts, uint64_t tstart, const char *unit, const char *format)
 {
 	ts->tstart = tstart;
 	ts->tend = tstart;
-	ts->interval = interval;
 	ts->unit = unit;
 	ts->format = format;
 }
 
 
-void timeseries_append(timeseries_t *ts, float value)
+void timeseries_append(timeseries_t *ts, uint64_t timestamp, float value)
 {
-	ts->data.push_back(value);
-	ts->tend += ts->interval;
+	ts->data.push_back( {timestamp, value} );
+	ts->tend = timestamp;
+
+	if(ts->data.size() == 1) {
+		ts->tstart = timestamp;
+	}
 }
 
 
-void timeseries_prune(timeseries_t *ts, float duration)
+void timeseries_prune(timeseries_t *ts, uint64_t duration)
 {
-	std::deque<float>::size_type to_keep = duration / ts->interval;
-	if(to_keep >= ts->data.size()) {
-		return;
+	timeseries_data_t::iterator iter = ts->data.begin();
+
+	uint64_t new_tstart = ts->tend - duration;
+
+	while(iter != ts->data.end() && iter->second < new_tstart) {
+		iter = ts->data.erase(iter);
 	}
 
-	std::deque<float>::size_type to_delete = ts->data.size() - to_keep;
-	ts->data.erase(ts->data.begin(), ts->data.begin() + to_delete);
-
-	ts->tstart += to_delete * ts->interval;
+	if(iter != ts->data.end()) {
+		ts->tstart = iter->first;
+	} else {
+		ts->tstart = ts->tend;
+	}
 }