Roads not flat so I disagree with your conclusion when viewed from such a shallow angle.
Do we agree that the cars going straight are in the center of their lanes?
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Where is the cyclist?
- Thread starter Daniel in SD
- Start date
Do we agree that the cars going straight are in the center of their lanes?
Must be a hell of a grade if the height changes much over 160 feet. Is there a hill or dip in the middle of the intersections? If it's just an up or down slope, that shouldn't affect the perspective.
I'm not sure they are centered in a lane after they pass the stop line in the oncoming lanes. There are no lane markings, and they might target the double yellow that is 150 feet away and drift toward it. Before the stop line, I would agree they are probably centered between the bike lane and the white divider lane.
It's the crown in the road that I think is the issue. The center of the road is higher.
So, we should be able to determine the distance from the cyclist to a car when they are the same distance away from the camera?
The turn lanes on each side of the intersection are about the same distance from the center line of the road, so crown should not affect perspective projection of the close turn lane to the other side of the intersection.
Crown is about 1/2inch over 12 inches which is about 2.4 degrees. The cosine is 0.999 so the crown is going to have little affect on lateral position.
There are intersections so you have different crowns. Seems much better to look at horizontal distance from other objects that we can actually see rather than extrapolated points on the road.
You can see from your drawing that small changes in the vertical position of cyclist dramatically change position estimation.
I would say that because of the complexity of this intersection, they would maintain the primary crown of folsom blvd.
Unfortunately I don't live in Sacramento so I can't go and inspect. And I don't really feel like making a 3d model to test my hypothesis. I'd much rather just use distance measurements to things we can directly see and know the exact sizes of.
This is the camera projection equation:
ImageX = f * x / z
ImageY = f * y / z
This assume that the camera is at the origin and not rotated. So the Image X position (left to right) of a point at a distance z from the the camera is a function of the focal length ( f ) of the camera, the distance from the camera (z) and the horizontal offset from the camera (x ). The vertical position does not enter into the Image X position.
I think the issue with your approach will be not knowing what the distances are from Brandon's car. But go on.
So if we can find the times where the cyclist and a car are the same distance from the camera we can determine the distance from cyclist to the car (since we know the width of the cars).
How accurately can we pick out the width of the vehicles from these low res images? Even more difficult for the cyclist. It's diffucult to tell precisely what the cyclist is next to. If you use a landmark that the car and bike pass at different times, Both car will have advanced between the two times. We could get the rough distance between the cars at their new postions, but that's not Brandon's new distance to the landmark.
I've included more of the lane lines on Brandon's side of the intersection to decrease the error from positioning my drawn lines along them. The camera has done all of the perspective calculations for us.
It just looks like to me he started the turn from his right side of the turn lane / white lane divider. I don't know. I could be wrong, but I don't think so.
But go on.
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If you look at the aerial view, you can see he is about to make a hairpin turn around the triangular island. By staying as close to the cars as possible he increases the radius of curvature of the turn substantially. Looks like he's moving pretty quickly.
Apparently he's ridden this course before.
Apparently he's ridden this course before.
AlanSubie4Life
Efficiency Obsessed Member
I don’t understand the point of this discussion? The cyclist was clearly in the left turn lane before entering the intersection. It’s legal and advisable on a bicycle traveling at speed to start the turn in such a way as to minimize the angle.
Personally, I think he was roughly in the middle of the lane at the beginning of the intersection, but in the intersection there are no marked lines for probably ~100 feet, so not sure what we are trying to determine here? He may have bobbed slightly to the right to do so but I don’t see a lot of evidence of that in the earlier picture that shows the two cars equidistant from Brandon’s vehicle, with the line measurements.
Why does this matter again?
Personally, I think he was roughly in the middle of the lane at the beginning of the intersection, but in the intersection there are no marked lines for probably ~100 feet, so not sure what we are trying to determine here? He may have bobbed slightly to the right to do so but I don’t see a lot of evidence of that in the earlier picture that shows the two cars equidistant from Brandon’s vehicle, with the line measurements.
Why does this matter again?
Some guy was making assertions about the bike obviously being in the left turn lane 8 secs before he turned and that both Bandon and fsd should have reacted appropriately. Perhaps you should ask him why it matters.
None of this is obvious because as the image above shows the bike was not in the left turn lane before he turned. I've drawn the lane markings in for you. He was riding next to the cars until he made the turn, trying to flatten out the curve.
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