04-09-2021, 12:40 PM | #1 |
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The picture below is a frozen frame of a DriveRecorder video.
It is divided in four images: - top left is front camera - top right is rear camera - bottom left is left side camera - bottom right is right side camera Now look closely at the two RIGHT pictures: in both you'll see a blue parking sign, but the top one (the rear camera) has an inverted "P", the bottom one has a correct "P" - and it is the same sign! In other words, the rear camera images are mirror-inverted, left with right. The main purpose of the max 40 second long DriveRecorder videos is to have some evidence in case of accidents. Watching an inverted rear video may not impress a jury... and a tampered one, edited to invert the image, even less so, as you may lose the attachement to the .json file - let me explain what I found out, and please correct me if I'm mistaken. To download a DriveRecorder file you go the the main iDrive menu, go to Apps, go to DriveRecorder and just follow the instructions - I used an usb C thumbdrive (FAT32 please!) plugged in the middle compartment. Each 40 sec video needs about 100 Mb. Each recording gets its own folder. The video files are .ts files, a simpler cousin of the usual .mp4 video files - and the Windows Photo & Movie app (or VLC, etc.) show them ok. All very easy once you tried it once. Together with each .ts file in its folder you'll find a .json file, which is a very simple animal: you can open it with Notepad and you will see many vertical blocks of obvious data updated some 30 times per second: timestamp, speed, gps coordinates - that's where you show the jury for each video frame where you were exactly and how fast, in extreme detail... As mentioned elsewhere, DriveRecorder is useless for parking surveillace or such: it has no image motion sensor and anyhow it cannot record more than some 50 events or so. To trigger a recording while driving is VERY simple: just a long push in the front camera button just ahead of the Start/ Stop button. The video recording will show what happened up to 20 seconds BEFORE you pushed the button. I hope BMW will fix the mirror inversion of the rear camera! |
04-10-2021, 09:58 AM | #3 |
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Interesting. While I certainly wouldn't put anything past a BMW bug (there are plenty of those in the car and new ones introduced every software update), my first thought is that this is not a bug, but perhaps a practical limitation. The mirrored top right image is the rear-facing camera and the non-mirrored bottom right image is the right mirror camera. If you mirror that top right (rear cam) image, it would place the P and the garage on the left side of the car, which is incorrect as it is clearly on the right side of the car in reality. I think the mirror view of the rear-facing camera is an artifact of processing that view into correct placement orientation.
Consider this thought experiment. In your forward-facing driving position, your right eye is towards forward and right of the car. The only way to view behind the car from that position is in the mirror which will, oddly enough, show you the mirror image of the behind. Now turn around and look backwards — in that position, it is now your left eye that is now positioned towards the right side of the car. That's the same thing that the rear camera sees, but your brain is able to process your body orientation change and the camera is not and, if left alone, would position car right scene on camera left ... which is incorrect from point of view of forward-facing observer, but is correct from the point of view of backwards-facing observer. Hence it is mirrored by the software so that you see the correct orientation from the point of view of a forward-facing (rather that backwards-facing) observer.
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04-10-2021, 11:00 AM | #4 | |
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04-10-2021, 11:10 AM | #5 |
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:-) OP was attentive, detailed, and precise in their post ... so I figured that deserved an alike response back. And it's an interesting example of how non-obvious our "obvious" and "common-sense" world is.
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04-10-2021, 11:27 AM | #6 | |
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04-10-2021, 11:46 AM | #7 |
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A couple of other tangential observations. First, I am sure a more precise way to demonstrate what's going on is with incident and reflected light vector diagrams, but it seems unnecessary to get into that in this case.
Second, if the display system was not simply a flat screen, but rather a VR setup that showed you your personal forward field of view while taking into account your varying head/body orientation, this problem would not exist (plenty of other problems would and do exist, however).
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04-10-2021, 05:47 PM | #8 | |
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If I had to use the rear image in real time, I would concur. However, I had the BMW dashcam in the former F85 and the image displayed in its PC software for the rear camera was as I would have seen it if I was seated facing backwards and looking through the rear window. Conversely, the DriveRecorder software shows a mirrored image, which for later viewing does not look useful to me; for instance, a closely following left hand drive car would be shown as a right hand drive one with inverted licence plate characters... But in recognition of the intelligent comment let me offer 'off topic' a pertinent riddle that my mother posed me a long time ago and that took me years to somewhat come to grips with it: "Why does a mirror invert left and right but does not invert top and bottom?" |
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04-10-2021, 09:05 PM | #9 |
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Probably the fastest and clearest answer :-)
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04-12-2021, 05:18 PM | #10 | |
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Then today I quietly asked myself "so, what was the actual explanation?" and I felt my IQ was about room temperature. Folks, please disregard my story on the DriveRecorder - it just works perfectly... 😇 |
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04-12-2021, 08:29 PM | #11 | ||
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