| CPC G01S 17/89 (2013.01) [G01S 17/42 (2013.01); G01S 17/86 (2020.01)] | 8 Claims | 

| 
               1. A detection method comprising: 
            measuring a first area with an infrared distance measuring sensor; 
                acquiring measured values of the first area; 
                acquiring three-dimensional coordinate values of at least two points in a second area included in the first area, the second area is smaller than the first area, based on the measured values; 
                calculating a position of a plane including the second area, based on the three-dimensional coordinate values of the at least two points; 
                deciding the position of the plane as a three-dimensional shape of the first area; 
                determining whether a ratio of a size of the second area to a size of the first area is equal to or lower than a threshold; and 
                notifying a user of a possibility that a detection accuracy for the three-dimensional shape of the first area is low, when the ratio is equal to or lower than the threshold. 
               |