Smaller node for single-bus voltage level (#55)

* Voltage level circle smaller if only one bus
* Update unit tests

Signed-off-by: Florian Dupuy <florian.dupuy@rte-france.com>

src/main/java/com/powsybl/nad/svg/SvgParameters.java

@@ -23,7 +23,7 @@ public class SvgParameters {
     private double arrowShift = 0.3;
     private double arrowLabelShift = 0.12;
     private double converterStationWidth = 0.6;
-    private double voltageLevelCircleRadius = 0.6;
+    private double voltageLevelCircleRadius = 0.3;
     private double fictitiousVoltageLevelCircleRadius = 0.15;
     private double transformerCircleRadius = 0.2;
     private double nodeHollowWidth = 0.1;

src/main/java/com/powsybl/nad/svg/SvgWriter.java

@@ -665,6 +665,10 @@ protected double getVoltageLevelCircleRadius(VoltageLevelNode vlNode) {
     }
 
     protected static double getVoltageLevelCircleRadius(VoltageLevelNode vlNode, SvgParameters svgParameters) {
-        return vlNode.isFictitious() ? svgParameters.getFictitiousVoltageLevelCircleRadius() : svgParameters.getVoltageLevelCircleRadius();
+        if (vlNode.isFictitious()) {
+            return svgParameters.getFictitiousVoltageLevelCircleRadius();
+        }
+        int nbBuses = vlNode.getBusNodes().size();
+        return Math.min(Math.max(nbBuses, 1), 2) * svgParameters.getVoltageLevelCircleRadius();
     }
 }