absolute distance

[garusuke]

I would like to know the absolute distance [m] from the output result. To do this, can I get it by doing pred_depth *= opt.pred_depth_scale_factor for the depth in the output of the disp_to_depth function? If this is ok, please tell me how to set the appropriate opt.pred_depth_scale_factor, and if not, how else?

[noahzn]

Hi, the method predicts relative depth values, not absolute distances. In the evaluation the code uses median filtering to scale the predicted depth values. I remember the authors of Monodepth2 said that this worked fine with KITTI. However, you can not use the monocular method to get accurate absolute distance. You can use stereo data for training to get absolute depth.

[garusuke]

Thanks for the reply. How do you code the median scaling? Could you please tell me the different parts of this code? The constant for depth_scale_factor is just assigned a value of 100/2.

MIN_DEPTH = 0.01
MAX_DEPTH = 100
min_disp = 1 / 100
max_disp = 1 / 0.01
scaled_disp = min_disp + (max_disp - min_disp) * disp
depth = 1 / scaled_disp
depth_scale_factor = 50
depth *= depth_scale_factor
depth[depth < MIN_DEPTH] = MIN_DEPTH 
depth[depth > MAX_DEPTH] = MAX_DEPTH

[noahzn]

The median scaling code is here. In the default code opt.pred_depth_scale_factor is set to 1, so we didn't use this scale factor.

[garusuke]

Are you saying that it is not possible to do median scaling an image for which the gt_depth is not known?

[noahzn]

Yes, you need to know the ground-truth. This is for the evaluation of predicted depth.

[garusuke]

I understand. Thank you very much. If we train in absolute distance, can we get depth in meters?

[noahzn]

Yes, you can get metric depth if you use supervised monocular training or stereo training.

[garusuke]

I understand. Thanks for everything.