Autoscale

src/main/java/de/ph87/data/series/graph/Graph.java

@@ -1,6 +1,7 @@
 package de.ph87.data.series.graph;
 
 import de.ph87.data.series.*;
+import de.ph87.data.value.*;
 import jakarta.annotation.*;
 import lombok.*;
 
@@ -59,6 +60,8 @@ public class Graph {
 
   public final int maxLabelWidth;
 
+  private final Autoscale autoscale;
+
   public Graph(@NonNull final SeriesDto series, @NonNull final List<GraphPoint> points, @NonNull final Aligned begin, @NonNull final Aligned end, final int width, final int height, final int border) {
     this.series = series;
     this.begin = begin;
@@ -67,21 +70,31 @@ public class Graph {
     this.height = height;
     this.border = border;
 
+    // find bounds
     double vSum = 0;
     double vMin = Double.MAX_VALUE;
     double vMax = Double.MIN_VALUE;
-    int maxLabelWidth = 80;
-    final FontMetrics fontMetrics = new BufferedImage(1, 1, BufferedImage.TYPE_INT_ARGB).getGraphics().getFontMetrics();
     for (final GraphPoint point : points) {
       vMin = Math.min(vMin, point.getValue());
       vMax = max(vMax, point.getValue());
       vSum += point.getValue();
-      maxLabelWidth = max(maxLabelWidth, fontMetrics.stringWidth(series.format(point.getValue())));
     }
-    this.valueAvg = vSum / points.size();
-    this.maxLabelWidth = maxLabelWidth;
 
-    widthInner = width - 3 * border - maxLabelWidth;
+    // auto scale
+    autoscale = new Autoscale(series.unit, vMin, vMax);
+    vMin *= autoscale.factor;
+    vMax *= autoscale.factor;
+    vSum *= autoscale.factor;
+
+    // find max label width
+    int __maxLabelWidth = 80;
+    final FontMetrics fontMetrics = new BufferedImage(1, 1, BufferedImage.TYPE_INT_ARGB).getGraphics().getFontMetrics();
+    for (final GraphPoint point : points) {
+      __maxLabelWidth = max(__maxLabelWidth, fontMetrics.stringWidth(autoscale.format(point.getValue() * autoscale.factor)));
+    }
+    this.maxLabelWidth = __maxLabelWidth;
+
+    widthInner = width - 3 * border - this.maxLabelWidth;
     heightInner = height - 2 * border;
 
     minuteMin = begin.date.toEpochSecond() / 60;
@@ -91,12 +104,14 @@ public class Graph {
 
     valueMin = vMin;
     valueMax = vMax;
-    valueRange = vMax - vMin;
+    valueAvg = vSum / points.size();
+    valueRange = valueMax - valueMin;
     valueScale = heightInner / valueRange;
 
-    this.points = points.stream().map(toPoint(minuteMin, minuteScale, vMin, valueScale)).toList();
+    this.points = points.stream().map(toPoint()).toList();
   }
 
+  @NonNull
   public BufferedImage draw() {
     final BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
     final Graphics2D g = (Graphics2D) image.getGraphics();
@@ -130,7 +145,7 @@ public class Graph {
   }
 
   private void yLabel(@NonNull final Graphics2D g, final double value, @Nullable final Stroke stroke, @Nullable final Color color) {
-    final String string = series.format(value);
+    final String string = autoscale.format(value);
     final int offset = maxLabelWidth - g.getFontMetrics().stringWidth(string);
     final int y = height - ((int) Math.round((value - valueMin) * valueScale) + border);
     g.setColor(color);
@@ -142,14 +157,14 @@ public class Graph {
   }
 
   @NonNull
-  private Function<GraphPoint, Point> toPoint(final long minuteMin, final double minuteScale, final double valueMin, final double valueScale) {
+  private Function<GraphPoint, Point> toPoint() {
     return point -> {
       final long minuteEpoch = point.getDate().toEpochSecond() / 60;
       final long minuteRelative = minuteEpoch - minuteMin;
       final double minuteScaled = minuteRelative * minuteScale;
       final int x = (int) Math.round(minuteScaled);
 
-      final double valueRelative = point.getValue() - valueMin;
+      final double valueRelative = point.getValue() * autoscale.factor - valueMin;
       final double valueScaled = valueRelative * valueScale;
       final int y = (int) Math.round(valueScaled);
 

src/main/java/de/ph87/data/value/Autoscale.java

@@ -0,0 +1,32 @@
+package de.ph87.data.value;
+
+import lombok.*;
+
+import java.util.*;
+
+@Data
+public class Autoscale {
+
+  public static final String[] SI_PREFIX = new String[]{"f", "n,", "µ", "m", "", "k", "M", "G", "T"};
+
+  public final double factor;
+
+  @NonNull
+  public final String unit;
+
+  public Autoscale(@NonNull final Unit sourceUnit, final double... values) {
+    final double abs = sourceUnit.factor * Arrays.stream(values).map(Math::abs).max().orElse(0);
+    final double exp = Math.max(0, Math.log10(abs));
+    final int group = (int) Math.floor(exp / 3);
+    this.factor = sourceUnit.factor * Math.pow(10, group * 3);
+
+    final int index = (SI_PREFIX.length - 1) / 2 + group;
+    this.unit = SI_PREFIX[index] + sourceUnit.base.unit;
+  }
+
+  @NonNull
+  public String format(final double value) {
+    return "%.1f %s".formatted(value, unit);
+  }
+
+}

src/main/java/de/ph87/data/value/Unit.java

@@ -9,21 +9,34 @@ import java.util.*;
 
 public enum Unit {
   TEMPERATURE_C("°C"),
-  PRESSURE_HPA("hPa"),
+
+  PRESSURE_PA("Pa"),
+  PRESSURE_HPA("hPa", 100, PRESSURE_PA),
+
   HUMIDITY_RELATIVE_PERCENT("%"),
-  HUMIDITY_ABSOLUTE_MGL("mg/L"),
-  HUMIDITY_ABSOLUTE_GM3("g/m³", 1, HUMIDITY_ABSOLUTE_MGL),
+
+  HUMIDITY_ABSOLUTE_GM3("g/m³"),
+  HUMIDITY_ABSOLUTE_MGL("mg/L", 1, HUMIDITY_ABSOLUTE_GM3),
+
   ILLUMINANCE_LUX("lux"),
+
   RESISTANCE_OHMS("Ω"),
+
   ALTITUDE_M("m"),
+  ALTITUDE_KM("km", 1000, ALTITUDE_M),
+
   POWER_W("W"),
   POWER_KW("kW", 1000, POWER_W),
-  ENERGY_WH("W"),
+
+  ENERGY_WH("Wh"),
   ENERGY_KWH("kWh", 1000, ENERGY_WH),
+
   IAQ("IAQ"),
   IAQ_CO2_EQUIVALENT("ppm"),
   IAQ_VOC_EQUIVALENT("ppm"),
+
   SUN_DC("Δ°C"),
+
   UNIT_PERCENT("%"),
   ;