diff --git a/mapview/2D/MV2DElementFloorUnderlay.h b/mapview/2D/MV2DElementFloorUnderlay.h
index 77be436..94f5858 100644
--- a/mapview/2D/MV2DElementFloorUnderlay.h
+++ b/mapview/2D/MV2DElementFloorUnderlay.h
@@ -20,6 +20,7 @@ private:
 	std::string tmpFile;
 	Floorplan::UnderlayImage* underlay;
 	BBox2 bbox;
+	float opacity = 0.5;
 
 	int selPoint = -1;
 
@@ -55,6 +56,9 @@ public:
 		selPoint = -1;	// clear selection
 	}
 
+	float getOpacity() const {return opacity;}
+	void setOpacity(const float o) {this->opacity = o;}
+
 	void paint(Painter& p) override {
 		(void) p;
 
@@ -101,9 +105,9 @@ public:
 			imgScaled = QImage();
 		}
 
-
-		float opacity = p.p->opacity();
-		p.p->setOpacity(0.50f);
+		// current opacity?
+		float _oldOpacity = p.p->opacity();
+		p.p->setOpacity(opacity);
 
 		// render downscaled image from cache? or use live-upscaling (faster, eats up less memory, ...)
 		if (imgScaled.width() > 0) {
@@ -113,7 +117,8 @@ public:
 			p.p->drawImage(QRectF(sx1, sy1-sh, sw, sh), img, QRectF(0,0,img.width(),img.height()));
 		}
 
-		p.p->setOpacity(opacity);
+		// reset
+		p.p->setOpacity(_oldOpacity);
 
 		// selected endpoint(s)?
 		if (hasFocus()) {
diff --git a/mapview/2D/tools/ToolSelector.h b/mapview/2D/tools/ToolSelector.h
index d86f000..fcb030f 100644
--- a/mapview/2D/tools/ToolSelector.h
+++ b/mapview/2D/tools/ToolSelector.h
@@ -282,6 +282,7 @@ private:
 
 		(void) m;
 
+		// currently: only accept keys when something is focused
 		if (focused) {
 
 			// pass it to the element which may consume this event
diff --git a/mapview/model/IHasParams.h b/mapview/model/IHasParams.h
index 8797823..296e526 100644
--- a/mapview/model/IHasParams.h
+++ b/mapview/model/IHasParams.h
@@ -104,7 +104,7 @@ public:
 	virtual ParamValue getParamValue(const int idx) const = 0;
 
 	/** set the idx-th param's value */
-	virtual void setParamValue(const int idx, const ParamValue& val) const = 0;
+	virtual void setParamValue(const int idx, const ParamValue& val) = 0;
 
 };
 
diff --git a/mapview/model/MMFloor.h b/mapview/model/MMFloor.h
index 778ee4d..adc978b 100644
--- a/mapview/model/MMFloor.h
+++ b/mapview/model/MMFloor.h
@@ -83,7 +83,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 		case 0: floor->name = val.toString(); break;
 		case 1: floor->height = val.toFloat(); break;
diff --git a/mapview/model/MMFloorAccessPoint.h b/mapview/model/MMFloorAccessPoint.h
index f71ab5c..edea9af 100644
--- a/mapview/model/MMFloorAccessPoint.h
+++ b/mapview/model/MMFloorAccessPoint.h
@@ -54,7 +54,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 		case 0: ap->name = val.toString(); break;
 		case 1: ap->mac = val.toString(); break;
diff --git a/mapview/model/MMFloorBeacon.h b/mapview/model/MMFloorBeacon.h
index fffe8a8..27b7b9e 100644
--- a/mapview/model/MMFloorBeacon.h
+++ b/mapview/model/MMFloorBeacon.h
@@ -56,7 +56,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 		case 0: b->name = val.toString(); break;
 		case 1: b->pos = val.toPoint3(); break;
diff --git a/mapview/model/MMFloorElevator.h b/mapview/model/MMFloorElevator.h
index c83a956..17ccaaa 100644
--- a/mapview/model/MMFloorElevator.h
+++ b/mapview/model/MMFloorElevator.h
@@ -47,7 +47,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 			case 0: elevator->width = val.toFloat(); break;
 			case 1: elevator->depth = val.toFloat(); break;
diff --git a/mapview/model/MMFloorFingerprintLocation.h b/mapview/model/MMFloorFingerprintLocation.h
index eeac267..dd5cc4b 100644
--- a/mapview/model/MMFloorFingerprintLocation.h
+++ b/mapview/model/MMFloorFingerprintLocation.h
@@ -49,7 +49,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 		case 0: fpl->name = val.toString(); break;
 		case 1: fpl->posOnFloor = val.toPoint2(); break;
diff --git a/mapview/model/MMFloorGroundTruthPoint.h b/mapview/model/MMFloorGroundTruthPoint.h
index 67ba358..1875ce9 100644
--- a/mapview/model/MMFloorGroundTruthPoint.h
+++ b/mapview/model/MMFloorGroundTruthPoint.h
@@ -42,7 +42,7 @@ public:
         throw 1;
     }
 
-    virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
         switch(idx) {
         case 0: gtp->id = val.toInt(); break;
         case 1: gtp->pos = val.toPoint3(); break;
diff --git a/mapview/model/MMFloorObstacleDoor.h b/mapview/model/MMFloorObstacleDoor.h
index d1816a5..1efb4da 100644
--- a/mapview/model/MMFloorObstacleDoor.h
+++ b/mapview/model/MMFloorObstacleDoor.h
@@ -70,7 +70,7 @@ public:
 	}
 
 	/** set the idx-th param's value */
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch (idx) {
 			case 0: break;
 			case 1: fo->height = val.toFloat(); break;
diff --git a/mapview/model/MMFloorObstacleLine.h b/mapview/model/MMFloorObstacleLine.h
index 31c165e..6de5d13 100644
--- a/mapview/model/MMFloorObstacleLine.h
+++ b/mapview/model/MMFloorObstacleLine.h
@@ -63,7 +63,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 		case 0: break;
 		}
diff --git a/mapview/model/MMFloorOutlinePolygon.h b/mapview/model/MMFloorOutlinePolygon.h
index 9cfb835..73578d2 100644
--- a/mapview/model/MMFloorOutlinePolygon.h
+++ b/mapview/model/MMFloorOutlinePolygon.h
@@ -57,7 +57,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 		case 0: fo->name = val.toString(); break;
 		case 1: fo->outdoor = val.toBool(); break;
diff --git a/mapview/model/MMFloorPOI.h b/mapview/model/MMFloorPOI.h
index 5f9184c..d26ab53 100644
--- a/mapview/model/MMFloorPOI.h
+++ b/mapview/model/MMFloorPOI.h
@@ -44,7 +44,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch(idx) {
 		case 0: poi->name = val.toString(); break;
 		case 1: poi->type = (Floorplan::POIType) val.toInt(); break;
diff --git a/mapview/model/MMFloorStair.h b/mapview/model/MMFloorStair.h
index 6d2fcb8..c43f6c6 100644
--- a/mapview/model/MMFloorStair.h
+++ b/mapview/model/MMFloorStair.h
@@ -66,7 +66,7 @@ public:
 		throw 1;
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		const int selPart = mv2d.getSelPart();
 		const int selNode = mv2d.getSelNode();
 		switch(idx) {
diff --git a/mapview/model/MMFloorUnderlayImage.h b/mapview/model/MMFloorUnderlayImage.h
index 34eafa4..5ca8db7 100644
--- a/mapview/model/MMFloorUnderlayImage.h
+++ b/mapview/model/MMFloorUnderlayImage.h
@@ -39,7 +39,9 @@ public:
 		;
 	}
 
-	int getNumParams() const override {return 4;}
+	int getNumParams() const override {
+		return 5;
+	}
 
 	virtual Param getParamDesc(const int idx) const override {
 		switch (idx) {
@@ -47,6 +49,7 @@ public:
 		case 1: return Param("scale X", ParamType::FLOAT);
 		case 2: return Param("scale Y", ParamType::FLOAT);
 		case 3: return Param("Anchor", ParamType::POINT2);
+		case 4: return Param("opacity", ParamType::FLOAT);
 		default: throw 1;
 		}
 	}
@@ -57,16 +60,18 @@ public:
 		case 1: return ParamValue(img->scaleX);
 		case 2: return ParamValue(img->scaleY);
 		case 3: return ParamValue(img->anchor);
+		case 4: return ParamValue(mv2d.getOpacity());
 		default: throw 1;
 		}
 	}
 
-	virtual void setParamValue(const int idx, const ParamValue& val) const override {
+	virtual void setParamValue(const int idx, const ParamValue& val) override {
 		switch (idx) {
 		case 0: img->filename = val.toString(); break;
 		case 1: img->scaleX = val.toFloat(); break;
 		case 2: img->scaleY = val.toFloat(); break;
 		case 3: img->anchor = val.toPoint2(); break;
+		case 4: mv2d.setOpacity(val.toFloat()); break;
 		default: throw 1;
 		}
 	}