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Joined: Apr 04, 2006 Posts: 10118 Location: Bexhill, South Sussex, UK
Posted: Tue Feb 03, 2015 3:18 pm Post subject:
@Howard.
It seems like your settings should not give too many false alerts, although having the ignore direction set would have increased them as you would get alerts for cams trapping in the other direction.
I'm not sure, but I think that the ignore direction, if set on, still takes into account your cone etc. settings so should only alert if you are travelling in the direction that the cam is set to trap to AND in the opposite direction. I don't think it works on a xx second circular radius, but I could be wrong.
Here's a recent example of what goes on 'behind the scenes' by the aforementioned unpaid volunteers . Im sure that the poster will not mind me quoting him in open forum, but I'll delete it if he does.
Quote:
A34/A4130 Milton Interchange, near Didcot, Oxfordshire
The following have all been submitted by Xxxx and me via CamerAlert:
South East direction
Add new Average camera (MY #5) at Lat:51.629711 Lon:-1.311059 Speed 70, Heading 157, This side.
Add new Average camera (MY #6) at Lat:51.621639 Lon:-1.305464 Speed 70, Heading 156, This side.
North West direction
Add new Average camera (MY #7) at Lat:51.603924 Lon:-1.2813 Speed 70, Heading 339, This side.
Add new Average camera (MY #8) at Lat:51.612946 Lon:-1.292055 Speed 70, Heading 310, This side.
Add new Average camera (MY #9) at Lat:51.616268 Lon:-1.298853 Speed 70, Heading 308, This side.
Add new Average camera (MY #10) at Lat:51.619713 Lon:-1.304276 Speed 70, Heading 331, This side.
Info for MaFt and fellow verifiers:
1. Xxxxx and I unexpectedly came across the SPECS system whilst travelling SE, I captured two SPECS but missed two. On the return trip, i.e. NW, we were ready for them so Xxxxxx, who was passenger, was able to capture all four on the A34 in NW direction.
2. There are two more SPECS in the SE direction of the A34 that need to be caught.
3. There are junction END SPECS (and presumably START SPECS) that need capturing.
4. There is are major "improvements" being done to the junction's roundabout (turning it into a hamburger layout).
5. Speed limit is currently 70mph on A34 but when roadworks start (sign stated 26 January 2015) there were 50mph and 40mph signs ready for use. The website even mentions 30mph Shocked! But until it starts we don't know. Will have to wait for submissions when it starts.
6. SPECS will be long term Temporary ones as Anticipated End Date\Time is 21 February 2016.
Joined: Feb 27, 2006 Posts: 14902 Location: Keynsham
Posted: Tue Feb 03, 2015 8:16 pm Post subject: Re: Thats interesting
hwalker1 wrote:
It gives the appearance of a professionally run one
[snip]
My cone is set at 23 degrees and the Direction Difference at 13 degrees,
[snip]
my set range of 40 seconds at 70MPH
I'm no expert, so the following may well be absolute drivel, but try it on for size just to humour me.
Cone 23 degrees - is that at one side, 12 degrees off to the side?
Direction Difference 13 degrees - would that imply that a camera at the extreme side (12 degrees) will register if it is aimed 13 degrees off that direction?
Would that add up to a camera pointing say 24 degrees away from your direction?
Range of 40 seconds at 70mph - would that be a distance of approx 1,365 yards? Or three quarters of a mile away?
Would that explain why I get warned of a 30mph camera half a mile off the M4 at Reading?
I could actually believe that, if only I had any confidence in my logic and maths - logic being that the Range Distance is "time to camera" at the speed I'm travelling (70mph), NOT the speed at which the camera is set to trap, so a 30mph camera warns at whatever distance my speed controls the range.
Joined: Apr 04, 2006 Posts: 10118 Location: Bexhill, South Sussex, UK
Posted: Tue Feb 03, 2015 10:30 pm Post subject: Re: Thats interesting
I understand it a little different to you Dennis.
Quote:
Would that add up to a camera pointing say 24 degrees away from your direction?
NO.
Lets say your cone is set to 24 degrees, this means that the camera must be less than 12 degrees to either side of your direction of travel i.e. pretty much straight ahead of you. If the camera is outside this limit CA will not alert.
Now take direction difference of 24 degrees and a camera on an overbridge. Assume your heading is due North (0 degrees) and the camera is trapping on the East/West bearing, then the direction difference is 90 degrees, so although the camera is well within your cone acceptance angle, it won't alert because the direction difference is too great.
But of course it will alert if the camera heading is given as 0 degrees. If the camera heading has been wrongly entered into the database as 15 degrees, it won't alert, as the direction difference is now greater than your setting of +- 12 degrees.
I think that the OP's apparently high 'false alarm' rate is high because he had 'ignore direction' set. I'm not certain but the name implies that so long as the camera is in your cone, it will alert, regardless of the direction the camera is 'pointing'. In this case, the camera on the aforementioned overbridge trapping East/West would alert.
A combination of a fairly tight 'cone' and 'direction difference' should (in theory) suppress a lot of real false alarms, but cameras 'around corners' might be suppressed as your heading and the camera trap 'heading' may be greater than your 'direction difference' setting. i.e. if the camera is just after a 15 degree bend, CA will not detect it until you round the bend enough so that your heading is within 12 degrees of the camera heading, which may or may not be too late, especially for a mobile. (All the above assumes that you have set both angles to 24 degrees)
There are also a lot of variable speed cams on at least one of the routes that the OP mentioned, all of them trapping his direction of travel, so he will get a lot of alerts because there are a lot of cams.
As to the 30MPH cams on a M'way. There are none that I can find on his routes, but there are a few close to the M'way on minor roads which might be the cause especially with 'ignore direction' set. But certainly not enough to cause a 30MPH alert every 20 yards, although I think that the OP has pretty much admitted that hi might have exaggerated a bit on that one.
Joined: Feb 27, 2006 Posts: 14902 Location: Keynsham
Posted: Wed Feb 04, 2015 9:18 am Post subject: Re: Thats interesting
M8TJT wrote:
I understand it a little different to you Dennis.
Quote:
Would that add up to a camera pointing say 24 degrees away from your direction?
NO.
Why not?
Allow a different example for my small mind.
I'm travelling on heading 100 degrees. My cone is 24 degrees, so the look ahead sweep covers an arc from 88 to 112 degrees. If I'm right about variance, a 20 degree variance will accept a camera at 112 degrees, pointing at 122 degrees.
I didn't design CamerAlert so I could well be wrong about that 122 degree camera, maybe it has to be pointing only at 112.
But my VERY important point is the Distance Time. I must surely be right in assuming that the distance time is governed by the vehicle speed, not the camera speed (otherwise you could be warned at a distance too short to slow down before hitting the camera). So at 70mph, the outreach distance is about 1,365 yards - well over three quarters of a mile. Taken to ridiculous lengths, if I set my warning distance time to two and a half hours, I'll be warned about that nasty camera in London. So false alarms are pretty much inevitable if CamerAlert is to be any good. Remember, for the PND version, we recommend settings of the camera speed times 10 to give 20 seconds warning. It's inaccurate because we do it at the camera speed, not the vehicle speed, but it's a pretty good rule of thumb.
So any camera within the cone/variance/distance parameters will alert.
So there. And I wish I had never started this, just because I react to anybody criticising CamerAlert, which I have admired ever since it was given to us (and is the SOLE reason why I bought an iPhone). _________________ Dennis
Joined: Apr 04, 2006 Posts: 10118 Location: Bexhill, South Sussex, UK
Posted: Wed Feb 04, 2015 11:05 am Post subject: Re: Thats interesting
DennisN wrote:
I'm travelling on heading 100 degrees. My cone is 24 degrees, so the look ahead sweep covers an arc from 88 to 112 degrees.
Agreed
Quote:
If I'm right about variance, a 20 degree variance will accept a camera at 112 degrees, pointing at 122 degrees.
No, it has to be pointing within your direction difference angle. So if we assume that you have set that to 20 degrees (+-10) it will alert only if the cam is pointing between 90 and 110, so your 112 cam will not alert even though it is within your 'look ahead' cone of 88 to 112
Quote:
But my VERY important point is the Distance Time. I must surely be right in assuming that the distance time is governed by the vehicle speed, not the camera speed (otherwise you could be warned at a distance too short to slow down before hitting the camera). So at 70mph, the outreach distance is about 1,365 yards - well over three quarters of a mile. Taken to ridiculous lengths, if I set my warning distance time to two and a half hours, I'll be warned about that nasty camera in London. So false alarms are pretty much inevitable ....
Agreed, but the cam must still fall within the 'look ahead cone and the direction difference parameters
Quote:
Remember, for the PND version, we recommend settings of the camera speed times 10 to give 20 seconds warning. It's inaccurate because we do it at the camera speed, not the vehicle speed, but it's a pretty good rule of thumb.So any camera within the cone/variance/distance parameters will alert.
Is there a CA for PND?Settings like this will give you a constant distance, not a constant time (but not on CA)
Quote:
So there. And I wish I had never started this, just because I react to anybody criticising CamerAlert, which I have admired ever since it was given to us (and is the SOLE reason why I bought an iPhone).
Agreed, but for iThing, read Android
As per what you intimated, the OP could also reduce his warning time, and as he doesn't seem too interested in mobiles, shorten it considerably, 15 -20 seconds should be enough to check and adjust your speed in necessary for a fixed cam.
Of course, I do accept that my interpretation of the parameters could be wrong and it would be good if lutz would confirm or deny this.
Joined: Feb 27, 2006 Posts: 14902 Location: Keynsham
Posted: Wed Feb 04, 2015 11:41 am Post subject: Re: Thats interesting
M8TJT wrote:
Is there a CA for PND?
Yes there is - perhaps before your time, but we used to download a zip file, unzip it and install it on our TomToms, Garmins and stuff. I do believe some people still don't have iThings and aThings, so they have a funny lump of a thing which sort of clings to their windscreens and somehow tells them how to get from A to B. _________________ Dennis
Posted: Wed Feb 04, 2015 2:44 pm Post subject: Re: Thats interesting
M8TJT wrote:
As per what you intimated, the OP could also reduce his warning time, and as he doesn't seem too interested in mobiles, shorten it considerably, 15 -20 seconds should be enough to check and adjust your speed in necessary for a fixed cam.
Of course, I do accept that my interpretation of the parameters could be wrong and it would be good if lutz would confirm or deny this.
As the OP concerned, all this is very interesting. I was informed that many cameras, especially those on the top of a rise can have a range exceeding 1000 yards. Which is why I set the time to camera at 40 seconds, having done the same calculation as Dennis. If fixed cameras don't need that distance then I will change it. I only use the system on motorways as I take great care never to exceed the speed limit on normal roads. However, on motorways I occasionally do so as the 70 limit is somewhat slow compared with most of Europe.
Joined: Apr 04, 2006 Posts: 10118 Location: Bexhill, South Sussex, UK
Posted: Wed Feb 04, 2015 3:17 pm Post subject:
The LTI 20-20 has a maximum display range of 999 metres (a little over 1000yds) and as a handheld, I suspect that It and its tripod mounted pals are actually used at a much shorter range than this.
Fixed cameras only work over a short range (several 10s of yards) Gatso type, after you have passed them and Truvelo type a short distance before you get to them.
But having said that, you are right in being concerned about the much longer range of the laser based mobile cameras. But whether you need 1,400 yards (40 sec at 70) warning is debateable.
Joined: Feb 27, 2006 Posts: 14902 Location: Keynsham
Posted: Wed Feb 04, 2015 7:28 pm Post subject:
Before I was granted the exalted status of an unpaid Verifier, I used to delete all 70mph cameras from my copy of the downloaded database (on my old fashioned PND ), because that's the maximum speed limit which we should all know, so there's no excuse for exceeding it, so I don't, because I'm a goody-two-shoes.
It won't be just on the brow of hills, it'll be far-seeing from a motorway overbridge. _________________ Dennis
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didn't know that! (PNDs)
), because that's the maximum speed limit which we should all know, so there's no excuse for exceeding it, so I don't, because I'm a goody-two-shoes.
