[ExI] crowdsourced crimefighters

[spike at rainier66.com]

Cool idea for amateur crimefighting math hipsters.

 

Given an image of the getaway vehicle taken at some unknown location, some
parameters are known, such as the diameter of the wheels (because those are
standard.)  

 

Consider the image of the rear wheel below.  

 

 



 

We know that rear wheel is on the plane of the vehicle.  The eye-brain
combination already knows that wheel is round, so it is perceived as a
circle, but a computer would see that wheel image as an ellipse with the
major axis (least foreshortening) forming an angle of about pi/6 from the
vertical edge of the image, and the minor axis (greatest foreshortening)
perpendicular to that.

 

Since we know the actual (standard) diameter of the rim, we can calculate a
scaling factor and pick off the distance from the camera to the center of
the rear wheel.  Since we know the height of the camera from the ground and
the distance of the center wheel from the ground, we have all the info we
need: two distances and an angle, or two angles and a distance, either will
get you home. 

 

Since we know the approximate length of the vehicle and the angle of the
plane of the rear wheel with respect to the axis of the POV of the camera,
we can use the distance to the center of the rear wheel and the angle of the
plane of that wheel with the line of sight, calculate a distance from the
camera to the headlight nacelle.  

 

Since we would now know the distance from the camera to the headlight
nacelle, we calculate the width from the top to the bottom of that nacelle,
and for bonus points, the dimensions of the running light cutout, or the
dimensions of any other high-contrast feature, the kind of stuff likely to
be visible on a night-photo, another example of which is the distance from
the front of the fender cutout to the rear of the fender cutout (both for
back and front of the vehicle.)

 

Dimensions of headlight nacelles, running light cutouts, wheelbase, etc, are
the kind of data which can be kept in a list.  Software can calculate the
angle to the camera POV and undo the foreshortening, thus calculating those
dimensions.  We can sooooo nail this perp.  Or rather figure out what kind
of car she drives.

 

spike

 

 

 

 

 

 

 

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