Perspective Compensation when Measuring Distances on an Image with a known reference distance

asked 2014-03-11 12:24:13 -0500

DigbySwift gravatar image

updated 2014-03-13 07:43:14 -0500

I am trying to calculate the real world distance of an arbitrary line drawn along the field of view from a one point perspective, single camera setup.

I will have a known distance running parallel. How can I find the compensation factor I need to apply to the pixel length of the measuring line?

Do I have to take into account the distance from the vanishing point, as the length per pixel increases the nearer you get to the vanishing point? Do I need to use the gradient of the known line to give me a rate of change?

I have been reading up on cross ratios but I don't understand if they are applicable in this scenario as I seem to be measuring in the opposite direction in respect to the vanishing point to apply this.

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Comments

1

you would also have to measure the radial distortion of the camera that was used.

GrumbleLion gravatar imageGrumbleLion ( 2014-03-13 12:28:37 -0500 )edit

Thanks. This doesn't have to be 100% accurate so I may just ignore the radial distortion at the moment as the camera doesn't distort that much. Once I can find the correct calculations I shall take that into account to improve accuracy.

DigbySwift gravatar imageDigbySwift ( 2014-03-14 05:54:49 -0500 )edit