# Analysis of the Leap Motion Controller Workspace for HRI Gesture Applications
## 6 Discussion  
In this paper, we evaluated the workspace of the Leap Motion Controller. This sensor is widely used in HMI interaction, and several studies have focused on its precision and accuracy; however, none of them evaluated the range of its workspace to its greatest extent (80 cm and higher). To achieve as realistic data as possible, we used an exact replica of a human operator's hand crafted by a professional sculptor.  
The results show that the proclaimed typical field of view 140 \(\times\) 120\({}^{\circ}\) is usable only in the range of 60 cm Euclidian distance from the origin of the LMC's coordinate system. The front view visualizations show that the tracking range on the x axis (left-right movement) is dependent on the hand being used and the level of stretch of the operator's fingers. In the range up to 60 cm, the right hand with a stretched thumb is more easily tracked on the negative side of the x axis (movement to the left). It is very likely that a left hand replica would behave similarly with the sides switched; however, in the range 60-80 cm, this behavior is no longer present. The side view results clearly show that hands are better trackable when the sensor sees the forearm. If the forearm is not seen, the tracking range is lower. Our measurements also show that the LMC is capable of tracking hands even above the maximum range of 60 cm, and in some cases, even up to 100 cm.  
Figure 14: All measurements: (**A**) (top–bottom view), (**B**) (front view). \(X,y,\) and \(z\) axis are in mm.  
Figure 15: All measurements: (**A**) (side view), (**B**) (overall view). \(X,y,\) and \(z\) axis are in mm.  
For the most precise results, according to our measurements, it is best to use the Leap Motion Controller in the ranges:  
* Left-right: X \(<\) -20 cm, +20 cm\(>\)
* Front-back: Y \(<\) -20 cm, +20 cm\(>\)
* Top-bottom: Z \(<\) 5 cm, +60 cm\(>\)  
For applications where high precision is necessary, the interface can be designed in such a way that it warns the operator when her or his hand is outside this range.  
In our approach, we use only a stretched palm gesture perpendicular to the plane where the LMC is positioned. Therefore, the limitation of our work is the use of only one gesture, and one hand size, which is the size of a male adult, 185 cm tall. We evaluate only static positions (to determine the size of the LMC's workspace), but we do not evaluate motion tracking. This could be accomplished by fixing the hand to the robot's end effector and repeating the same motions. In the future, rotations, and possibly other gestures and hand sizes (male, female, child), could be used to gather more information about the tracking behavior of the LMC.  
Conceptualization, M.T.; methodology, M.T.; software, M.T.; validation, M.D.; formal analysis, M.T. and M.D.; investigation, M.T.; resources, M.T.; data curation, M.D.; writing--original draft preparation, M.T.; writing--review and editing, M.T. and M.D.; visualization, M.D.; supervision, M.T.; project administration, M.T.; funding acquisition, M.D., J.R. and F.D. All authors have read and agreed to the published version of the manuscript.  
This article was written thanks to the generous support under the Operational Program Integrated Infrastructure for the project: \"Research and development of the applicability of autonomous flying vehicles in the fight against the pandemic caused by COVID-19\", Project no. 313011 ATR9, co-financed by the European Regional Development Fund. Further funding by KEGA 028 STU-4/2022 and APVV-21-0352.  
Not applicable.  
The authors declare no conflict of interest.