GPS Logger creates a crazy map in GoogleMaps. Why?!

HerrLehmann's picture

Hey guys,

i just received my new GPS-Logger. But iam not happy because of the crazy results.
I made a screenshot for you. You can see, that there are a lot of Positions but i have not moved the GPS Logger.
I mean, it should give out the same result until i move it.

Do you unterstand the Problem?
-> I dont move the GPS logger und there are a lot of different positions.

Do you now a Solution or a Setting i can change?

Thanks a lot,

Hr. Lehmann

mdeweerd's picture

"NOrmal" behaviour when not moving


Unfortunately this is the 'normal behaviour' when not moving. It can jump around in an area that stretches some 10-15 meter on each side.

I sometimes manage to reduce this by setting a minimum HDOP or PDOP value in the filter of BT747. Further, I log positions based on distance or speed - not based on time. I set the distance condition to 10 meter (you could set it to 5) and the speed condition to 4-5 km/h. That way I will log less positions when not moving and more when moving. At low speeds I log only every 10 meters but that is acceptable to me.

Thanks a lot for your

Thanks a lot for your professional answer.
I changed my settings to this: Speed: 5 and meters: 10.

So. Now i want to set the filter. What values do you use for HDOP and PDOP? I have no idea.

After I know that, i'll make a little test-drive with my car.

Thank you!

Hr. lehmann

mdeweerd's picture

HDOP / PDOP Filter values

You only need to log one of these ("log format"). Currently I only log HDOP because I am most interested in the horizontal precision. I did not notice a substantial difference when using PDOP to select best positions.

The filtering is done AFTER the trip. You will still record all the positions, but in BT747 the advanced filter will limit the positions that you actually use for the track.

Personally I use 1.96 as a limit. That is a value that I sometimes adjust to a smaller value - sometimes as low as 1. The best value may depend a bit on your logger. Why 1.96? Because 1.95 values seemed acceptable and 2.00 values not.

Hello again, i tried it and

Hello again,

i tried it and it seems to be working.
But there are positions connected with a red line on the map, thats means, that there are positions missing. Why?

And the last question :-) : In BT747 is an Counter for the used Discspace and a layer like: "0%". Is the number (e.g. 700 (0%)) standing for Positions or for bytes?

Thanks a lot and sorry for my english,

Hr. lehmann

mdeweerd's picture

Red line

Your English is pretty good - better than my German.

The red line indicates that there were positions in the log that were not kept for the final track. This is interesting in case you want to see where positions were skipped (e.g., because the HDOP is too big) - in some cases this indicates a tunnel for instance.
You can avoid the red line by setting the same 'blue' color (or whatever other color you choose) when you change the 'Bad color' color (Output Settings tab in English).

Regarding the memory indication: in the latest versions this is for the number of positions - when you hover over the value with your mouse you will see memory usage. This does not correspond to disk space, but to the usage of the flash memory (which is not a disk).