Filter (Distance) - Actual Scenario how does it work?

Dear All,

The filter option, Distance by default is set to 50 mtr in Conf file.

What does it do in reality.

1. does it mean, that for a particular device if a position sent, is less than 50 mtrs away from the previously sent position, then this position is discarded and or not stored?

2. If thats the case, wouldn't that give a wrong report when calculating total distance from the position table.

3. And if not what is the minimum distance best configuration value for this filter.

4. If this is disabled, then would it affect the positions recorded in anyway or reports generated in anyway.

1. Correct, if the position is less than 50 meters from the last recorded one then it's ignored.

2. There might be a bigger error in distance calculation in some cases, but in other cases it actually can give better results.

3. I don't know. You should tell me what's the best value.

4. If filtering is disabled it won't affect anything.

Thanks for the information, Anton :)

For point 2, I am curious to know in what possible cases (maybe an example, of where there could be a bigger error in distance calculation) if set to 50mtr, just for my knowledge.

For Point 3, I had it running for last 20 days at 50mtr itself, today I have changed it 5 mtr (to try and see what happens), Not sure if its the best value.

The reason why I decide to switch it to 5mtr are.

1. On real time map with a polyline (Trace behind the vehicle), I am able to draw the line then more presisely sticking to the road, than of the road.
2. Reports (I assume, could be more accurate, considering towns where narrow roads but empty roads exist) where the driver could take a huge turn and cover a lot of distance at the curve/turn) between two updates in cases where update frequqncies from the tracker is set to high.

Regarding point 2,

Case 1:
When device is moving with filtering you would result in less points and obviously the distance would be less accurate.

Case 2:
When device is stationary, because of the way GPS works, it can give slightly different coordinates every time (say within 10 meters radius). So, if you leave device for a long time, the error accumulates and can result in a big distance even though device hasn't actually moved.

For case 1, let me write an example, just to clarify:

I enable filter and set it for 25m.

If the las stored position is lets say (0,0)m and a new position comes along with (0,100)m then the new position (0,100)m is stored. Then the device stops, but GPS variation gives you (0,98)m for that position, then the filter acts, and no data is saved, because the variation is only 2m.

(I am assuming there is some more complex calculation because the position is not stored in meters, it is just a simplification.)

Another question, which conditional comes first, the distance filter or the invalid filter?

Your example is correct.

All filtering is done at the same time.

What is the main goal of the distance filter? Is it to avoid hundreds of points in a small radius when the device is parked (specially under some concrete that blocks GPS) ?

Yes.

Anton, let me ask you a question regarding this issue. If filter is set to 50 mts and vehicule is parked and it reports position 55 mts away from previous location (due to inaccuracy of, lets say, 300 mts), the coordinates will be taken as valid because they are outside the filter even if they are wrong......how do you recommend to handle this in order to calculate distance ?

Not sure what kind of answer you are expecting. I don't think anything can be done other than increasing threshold.

I just wanna be sure there is nothing we can do. Thanks