Newbie Question (how much warning)

will help you.

First go to
http://www.poi-factory.com/node/6507
and read it.

Then go to
http://www.poi-factory.com/node/30728
and read it.

one quarter mile is the default but you can override that distance if you desire.

Appreciate your quick response. I removed then re-installed the POI's using the manually inputed information recommended. I will check it out tomorrow. Somehow I missed the information quoted. thank you for your forbearance.

And welcome to the site

Notice the POI Factory Redlight-Cameras.csv file has the word “Redlight” in the file name. Based on that word in the name, POIs in the file installed on a GPSr using POI Loader in the express mode will all have an alert distance of ¼ mile.

The amount of “warning” time you would have depends on the speed you are driving and whether you slow down when you hear the alert.

If you continue at the speed you were driving, the amount of time to reach the red light can be calculated by the formula:

Time (seconds) = 900/speed (mph)

Thus if you continued driving:

30 mph the time to reach the red light is 30 seconds.
35 mph the time to reach the red light is about 26 seconds
45 mph the time to reach the red light is 20 seconds

If you started slowing down immediately after the alert sounded and did so at a constant deceleration rate such that you would come to a stop right at the light, then you can multiply the above times by 2.

Speed lights are different. POI Loader calculates the alert distance based on “speed information” in the poi, poi file name, or given in the manual mode.

The Poi Factory Speed-Camera.csv file has “speed information” in the form of “@speed” in the name field of individual Pois in the file. Example: @30 gives an alert speed of 30mph

The alert distance calculated by POI Loader is the distance that would be traveled while driving at the alert speed for 36 seconds.

The resulting formula for calculating the alert distance is:

Alert distance (miles) = alert speed (mph) divided by 100

Alert distances for alert speeds from 0 to 20 are calculated based on 20mph, which results in a distance of 0.2 miles (1056 feet.)

As to the amount of time, speed alerts will give you “36 seconds warning” if you were driving at the alert speed and continued at that speed until you reach the light. (You would have to be driving little above the alert speed to trigger the alert.)

If you were driving faster than the alert speed and continued to drive at that speed the amount of time it would take to reach the light can be calculated by the formula:

Time (seconds) = [{alert speed} divided by {driving speed}] multiplied by 36

For example, if the alert speed was 20 and you were driving:

30 the time is 24 seconds
35 the time is 21 seconds
60 the time is 12 seconds

If you started slowing down immediately after the alert sounded and did so at a constant deceleration rate such that you would slow down to the alert speed just when you came to the camera, then you can multiply the above times by 2.

If you install the POI with POI loader in the manual mode you set the distance in feet to the camera. I use 1250 feet to give me time to slow down with ease.

That would work with files with RedLight in their name but would not work with the POI Factory speed camera csv file. The manual setting will not over ride the @speed information in the poi names inside the file.

I'm not so sure anymore about files with the @ symbol anymore. Over the last several months I have noticed my 885 alerting me approximately 400 meters before a speed camera regardless of the @ value. The @ value only determines the color of the alert and if it continually repeats.

I don’t know about the 885 but on my 255W the @speed works “as advertised”.

Are you sure the syntax is correct in each line? What is the name of the file?

I would be interested to see several lines of your csv file(s) for different speeds.

It's the file from here. It's modified slightly in that I use Sir Kull's formula to add 5 to each of the values. In order to do that, you have to remove the value added to the end of each line first.

The 8XX series uses a different operating system than the standard Nuvi line. The 8XX's were built using a UNIX operating system.

Would you post some of the modified lines?

I think the 200 series are UNIX based. Gamin lists the 8xx series as Linux based, but I would not think that would make any difference in how Poi Loader would handle csv speed alert files.

RE: http://developer.garmin.com/linux/

Let's not hijack the thread.

WOW ... I'm now in information overload. So much math so little time..

Now I need coffee.

Get a grip! The above is just plain arithmetic i.e. multiplication and division.

It is a good thing that I did not show the mathematics I used to derive the formulas. You would need some Irish in your coffee for that.

And if I went into the mathematics required to calculate the time to travel a given distance when the deceleration rate is not constant, you would have to leave out the coffee and go for the undiluted Irish.

Thanks for all the interesting thoughts, it was exactly what I was looking for. I appreciate the experience level of the people that have responded.

Welcome to the site.

Correction:

The factor of 2 applies only if the alert speed is zero.

For other alert speeds the factor is [{driving speed when alert sounded} divided by {alert speed + driving speed when alert sounded}] x2

Example: for driving speed when alert sounded = 35 and alert speed = 20 the factor would be:

[35/(35+20)]2 = 1.27

Of course the time for this case can be calculated directly by this formula:

time (seconds) = [2x{alert speed}/{alert speed + driving speed when alert triggered}]x36

A commonly told story is that you get an alert distance that gives you a 36 second warning based on the driving speed.

Now you know the rest of the story. That is, you get an alert distance based on the alert speed, and you only get 36 seconds warning if you are driving at the alert speed when the alert sounds and you continue on to the alert poi at that speed.

And the amount of time you actually get has to be calculated using different formulas depending on what you do after the alert sounds.

The above calculations are for two simple cases: continuing on at the same speed; and uniformly slowing down to the alert speed by the time you reach the alert poi.

An infinite number of other scenarios are possible such as coasting for a while and then hitting the brakes hard, or hitting the brakes lightly for a while then coasting and finally braking harder at the last, and so on.

Because of all the different things a driver might do after hearing the alert, there is no way that a GPSr could calculate a distance that would give you 36 seconds warning. That is probably why Garmin has POI Loader calculate the alert distance based on the alert speed as indicated above.

One of the conditions that may reflect on my experience is that most of the cameras in my area would generate an alert approximately 400 meters from the camera location if you were traveling at the posted speed. A Mark I uncalibrated eyeball isn't that great for judging distances when you have to guess where the endpoint is as well.

Playing with the numbers, and assuming a 36 second alert radius at the alert speed, a 35 MPH speed camera will alert approximately 1800 feet from the camera. That's actually a little over a third of a mile, but then I haven't calibrated my eyeball since I got new glasses either. So maybe the @ speed value is working as advertised. The alert distance is dependent on the speed value.

000658 You don't have to make the run manually.
Go to tools then go to settings then go to system.
Then turn simulator on.Now punch in where you want to go punch go and your garmin will make a dry run.
I hope this helps it works for me. good luck Cliff

I use 1320ft. which is far enough for me to respond.

With the pointers here I am learning more each day. for my purposes, in town, 1000 feet seems more than enough for me. In a few days I am going to install the voice warning. The tips here have been exceptional and I thank you all. I will be giving it a real work out this next month as I am traveling to other parts of the country for work.

The sparcity of your statement begs these questions:

Which of the POI Factory red light and speed camera csv files do you use? Or does it apply to both?

If it applies to the red light one, the default due the word Redlight in the name automatically provides an alert distance of 1320 ft. Are you using the default or are you setting the distance using POI Loader’s manual mode?

For what range of driving speeds is it “far enough for me to respond”? I think that is ok for red lights in towns and cities but what about those on open country two lane highways where you encounter red lights ahead while you are driving 65 mph?

If it applies to the speed camera one, how do you override the distances that are calculated per the @speed information in the name fields of Speed-Cameras.csv?

I downloaded and installed both the redlight and the speed camera files. I have set the alert distance to 1000 feet using the POI Loaders manual mode which seems enough for the around town driving that I do. If I find that the distance is not sufficient for more rural areas, I will reload the files using the standard settings. My distance settings are more of a trial and error learning experience for me and not any sort of a recommendfation for anyone else.

The last question is beyond my scope of knowledge, however I am sure that others here can answere that question.

I was not asking how to do that, I was saying that the brief post Cyberian75 made begs those questions. HIS answers to those questions would be needed to make his post useful.

Be aware that if you set the proximity alert distance for the Speed Cameras.csv file to 1000 feet (or any other distance) using manual mode, the distance will be ignored and you will get the same result you would have gotten had you run POI Loader in the express mode. That is, the alert distances will be based on the alert speed given in the name field of each record inside the Speed Cameras.csv file.

If you are loading both csv files in the same POI Loader session, you can set the distance for the Redlight one to whatever you want but when you are asked for the settings for the speed one you may as well uncheck both square boxes and chose "Next".