US open tennis: comments on the mac cam "challenge" system used...

[tmc]

this is a gr8 system and i appreciate the technology. and yes i think it should used in all games. however...

this system shows the shadow (the projection of the ball on the ground) of the ball on the ground and even if the shadow "just" touches the line it is considered as "in".

well, thats where i think it is "buggy". i think the diameter of the shadow is that of the diameter of the ball (sphere). we all know whenever a sphere (ball) touches a plane (ground), the area of contact will be [much] smaller than the actual diameter of the sphere. in fact it will vary on how much pressure is applied on the ball. so, technically, the ball will still be out, but since the shadow touches the line it is considered "in". i think this is wrong. thats why referees give it as out, whereas the system says "in" sometimes. imho, this needs to be fixed - say by taking the center point of the circle to decide whether it is in or out, etc.

what do you think? thanks.

 

[FoBoT]

shadow? the shadow has to be in or out?

i thought the ball had to be in or out

isn't the most important thing that the method used to determine in/out be consistent? human judges will generally be less consistant than a machine, for the most part. if the machine is good

 

[mugs]

If you took the center point you'd err in the other direction - calling balls out when they're in.

I haven't been watching the US Open, but based on what you said I'll say this - it's more accurate than any human could be.

 

[DBL]

How does it show the shadow? From what I saw, it seems to show the area of the ball which makes contact with the ground.

 

[Yourself]

The ball "squishes" and skids into the shape you see when it hits the ground. It doesn't stay round....

 

[Slick5150]

If you've ever seen a tennis ball hit the ground at those speeds in slow motion, you'd know that it compresses heavily making the surface area of the ball touching the ground much larger, making the "shadow" they show on the replay a pretty accurate representation of the balls contact.

 

[mugs]

Originally posted by: FoBoT

isn't the most important thing that the method used to determine in/out be consistent? human judges will generally be less consistant than a machine, for the most part. if the machine is good

Yeah pretty much. A bad call at a bad time against a player who can't control their emotions could easily cost them the match. The system the OP is describing could take that factor out (assuming the players have confidence in the system's accuracy, which they probably won't)

 

[tmc]

Originally posted by: DBL
How does it show the shadow? From what I saw, it seems to show the area of the ball which makes contact with the ground.

if it is the area of the ball that comes into contact with the ground, then it is perfect. thats what it should be.

but, i don't think it is that way. it is the projection of the ball on to the ground - which is much more than the area of the ball that comes into contact with the ground.

 

[tmc]

Originally posted by: Slick5150
If you've ever seen a tennis ball hit the ground at those speeds in slow motion, you'd know that it compresses heavily making the surface area of the ball touching the ground much larger, making the "shadow" they show on the replay a pretty accurate representation of the balls contact.

then, in that case, for a drop shot, the shadow should be much smaller? somehow, i think the size of the shadow is the same in all cases, and hence my doubt.

 

[Yourself]

Originally posted by: tmc

Originally posted by: DBL
How does it show the shadow? From what I saw, it seems to show the area of the ball which makes contact with the ground.

if it is the area of the ball that comes into contact with the ground, then it is perfect. thats what it should be.

but, i don't think it is that way. it is the projection of the ball on to the ground - which is much more than the area of the ball that comes into contact with the ground.

See above...the ball does not stay round when it hits. It elongates....hence the shape of the ball mark on the replay...

**Edit**

I agree a drop shop or a lob should have more of a round shape in the replay...

 

[tmc]

Originally posted by: Yourself

Originally posted by: tmc

Originally posted by: DBL
How does it show the shadow? From what I saw, it seems to show the area of the ball which makes contact with the ground.

if it is the area of the ball that comes into contact with the ground, then it is perfect. thats what it should be.

but, i don't think it is that way. it is the projection of the ball on to the ground - which is much more than the area of the ball that comes into contact with the ground.

See above...the ball does not stay round when it hits. It elongates....hence the shape of the ball mark on the replay...

**Edit**

I agree a drop shop or a lob should have more of a round shape in the replay...

fully, agree with your say that - it should be aquishy and all.

however, that is not the case from what i see. it is almost always round, and the size is almost of the diameter of the tennis ball. i agree that the ball compresses and all, so that the point of contact with the ground is not a point, but a "sort of" circle, but i highly doubt if the diameter of the circle will be as big as the diameter of the tennis ball. if it were true, then that means the ball almost becomes half on the point of contact - as thats when the diameters will be same. and i don't think somebody can compress the ball that much.

 

[DBL]

Originally posted by: tmc

Originally posted by: DBL
How does it show the shadow? From what I saw, it seems to show the area of the ball which makes contact with the ground.

if it is the area of the ball that comes into contact with the ground, then it is perfect. thats what it should be.

but, i don't think it is that way. it is the projection of the ball on to the ground - which is much more than the area of the ball that comes into contact with the ground.

No. The tech uses multiple cameras to determine the ball position to a very high degree of certainty. It's got nothing to do with shadows.