I need to convert the distance between object and camera from pixels to meter/cm frame by frame and then calculate the speed of moving object. In the first frame, the distance of object from camera is 4 meter, and Focal length FL 8mm, width of the object is 0.0373 meters. What I did first to calculate the projection of object:
focal_length_px = 8000/4.8 #Focal length(px): 8mm / (4.8 µm / px) = 1667px =: f
Object :
object_reall_width = 0.0373 # Width: 0.0373m
distance = 4 # Distance: 4m
obj_width_px = (object_reall_width/distance) * focal_length_px # Projection of object(px): (0.0373 m / 4 m) * focal_length_px = 15.5 px
After object detection, I want to calculate the distance. I used the distance_finder() code in this link.
def distance_finder(focal_length, real_obj_width, obj_width_in_frame):
distance = (real_obj_width * focal_length) / obj_width_in_frame
return distance
and the output is:
obj_width_in_frame = 17
obj_dst = distance_finder(focal_length_px, obj_width_px, obj_width_in_frame) # obj_dst = 1523.6928104575165
My question is: how to convert the object distance in the frame from the camera (obj_dst = 1523.69) from pixels to meters/cm?
and then calculate the speed of object in the frame.
We discussed the math before. Now you just need to rearrange some equations.
Pinhole camera model.
Object:
Solve for physical distance, let's call it d.
(0.0373 m / d) * f = 17 px, which we already had (replace previous 4 meters by d, insert 17 px as known)d = (0.0373 m) / (17 px / f) = 0.0373 m * f / 17 px=> d ~= 3.66 meters
This equation is already implemented in your function distance_finder(). It is the same expression.