diff --git a/synthetic/SyntheticPath.h b/synthetic/SyntheticPath.h
index fd50715..f194729 100644
--- a/synthetic/SyntheticPath.h
+++ b/synthetic/SyntheticPath.h
@@ -4,18 +4,23 @@
 #include "../math/Interpolator.h"
 #include "../floorplan/v2/Floorplan.h"
 #include "../floorplan/v2/FloorplanHelper.h"
+#include "../floorplan/v2/FloorplanHelper.h"
 
 /** allows interpolation along a synthetic path */
 class SyntheticPath : private Interpolator<float, Point3> {
 
 	using Base = Interpolator<float, Point3>;
 	using Entry = Base::InterpolatorEntry;
+	const Floorplan::IndoorMap* map;
+
 
 public:
 
 	/** create path using the given ground-truth points from the map */
 	void create(const Floorplan::IndoorMap* map, std::vector<int> ids) {
 
+		this->map = map;
+
 		// get all ground-truth points from the map
 		auto gtps = FloorplanHelper::getGroundTruthPoints(map);
 		float dist = 0;
@@ -38,6 +43,8 @@ public:
 		return Base::getEntries();
 	}
 
+
+
 	/** smooth harsh angles */
 	void smooth(float delta = 1, int numRuns = 1) {
 
@@ -104,6 +111,16 @@ public:
 		return Base::get(distance);
 	}
 
+	/** is the given position part of a floor (or in the air) */
+	bool isOnFloor(const float distance) const {
+		const Point3 pos = getPosAfterDistance(distance);
+		for (const Floorplan::Floor* floor : map->floors) {
+			const float delta = std::abs(floor->atHeight - pos.z);
+			if (delta < 0.1) {return true;}
+		}
+		return false;
+	}
+
 };
 
 #endif // INDOOR_SYNTEHTICPATH_H
diff --git a/synthetic/SyntheticSteps.h b/synthetic/SyntheticSteps.h
index 7bfb885..ee0ad51 100644
--- a/synthetic/SyntheticSteps.h
+++ b/synthetic/SyntheticSteps.h
@@ -25,8 +25,11 @@ private:
 	/** the walker to listen to */
 	SyntheticWalker* walker;
 
-	/** the pedestrian's step-size (in meter) */
-	float stepSize_m = 0.7;
+	///** the pedestrian's step-size (in meter) */
+	//float stepSize_m = 0;
+
+	///** when walking stairs, the step size is much smaller */
+	//float stepSizeStair_m = 0;
 
 	float lastStepAtDistance = 0;
 
@@ -46,13 +49,14 @@ private:
 	//float stepSizeSigma_m;
 	float noiseLevel;
 	Distribution::Normal<float> dNextStep;
+	Distribution::Normal<float> dNextStepStair;
 
 public:
 
 	/** ctor with the walker to follow */
-	SyntheticSteps(SyntheticWalker* walker, const float stepSize_m = 0.7, const float stepSizeSigma_m = 0.1, const float noiseLevel = 0.33) :
+	SyntheticSteps(SyntheticWalker* walker, const float stepSize_m = 0.7, const float stepSizeStair_m = 0.3, const float stepSizeSigma_m = 0.1, const float noiseLevel = 0.33) :
 		//stepSize_m(stepSize_m), drift(drift), stepSizeSigma_m(stepSizeSigma_m),
-		noiseLevel(noiseLevel), dNextStep(stepSize_m, stepSizeSigma_m) {
+		noiseLevel(noiseLevel), dNextStep(stepSize_m, stepSizeSigma_m), dNextStepStair(stepSizeStair_m, stepSizeSigma_m) {
 
 		walker->addListener(this);
 		dX.setSeed(1);
@@ -87,10 +91,11 @@ public:
 protected:
 
 
-	void onWalk(const Timestamp walkedTime, float walkedDistance, const Point3 curPos) override {
+	void onWalk(const Timestamp walkedTime, float walkedDistance, const Point3 curPos, const SyntheticWalker::Type type) override {
 
 		(void) curPos;
-		const float nextStepAt = lastStepAtDistance + dNextStep.draw();
+		const float distAdd = (type == SyntheticWalker::Type::FLOOR) ? (dNextStep.draw()) : (dNextStepStair.draw());
+		const float nextStepAt = lastStepAtDistance + distAdd;
 
 		// 1st, start with random noise on the accelerometer
 		const float x = dX.draw();
diff --git a/synthetic/SyntheticTurns.h b/synthetic/SyntheticTurns.h
index d9d8ef8..ba8beb0 100644
--- a/synthetic/SyntheticTurns.h
+++ b/synthetic/SyntheticTurns.h
@@ -85,7 +85,7 @@ protected:
 		return val;
 	}
 
-	void onWalk(const Timestamp walkedTime, float walkedDistance, const Point3 curPos) override {
+	void onWalk(const Timestamp walkedTime, float walkedDistance, const Point3 curPos, const SyntheticWalker::Type type) override {
 
 		// time sine last onWalk();
 		if (lastTs.isZero()) {lastTs = walkedTime; return;}
diff --git a/synthetic/SyntheticWalker.h b/synthetic/SyntheticWalker.h
index 2bb5c1e..0e290c8 100644
--- a/synthetic/SyntheticWalker.h
+++ b/synthetic/SyntheticWalker.h
@@ -8,9 +8,14 @@ class SyntheticWalker {
 
 public:
 
+	enum class Type {
+		FLOOR,
+		NON_FLOOR,
+	};
+
 	class Listener {
 	public:
-		virtual void onWalk(Timestamp walkedTime, float walkedDistance, const Point3 curPos) = 0;
+		virtual void onWalk(Timestamp walkedTime, float walkedDistance, const Point3 curPos, const Type type) = 0;
 	};
 
 private:
@@ -55,11 +60,13 @@ public:
 
 		// get the current position along the path
 		const Point3 curPosOnPath = path.getPosAfterDistance(this->walkedDistance);
+		const bool isOnFloor = path.isOnFloor(this->walkedDistance);
+		const Type type = (isOnFloor) ? (Type::FLOOR) : (Type::NON_FLOOR);
 
 		Log::add(name, "walkTime: " + std::to_string(walkedTime.sec()) + " walkDistance: " + std::to_string(walkedDistance) + " -> " + curPosOnPath.asString() );
 
 		// inform listener
-		for (Listener* l : listeners) {l->onWalk(walkedTime, walkedDistance, curPosOnPath);}
+		for (Listener* l : listeners) {l->onWalk(walkedTime, walkedDistance, curPosOnPath, type);}
 
 		return curPosOnPath;