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Best way to filter out "spikes"?

gpsn00b's picture
Sat, 06/12/2010 - 03:33 — gpsn00b

Re,

What's the best way to filter out major spikes (one point the fix is great and shows the exact location but a second after I see myself about 5km away, then back to normal)?

Also, I saw a thread but can't locate it anymore where it was described how to set 747A+ to update @ 5Hz. What are the suggested "Advanced Device Settings" for the 5Hz mode as well as the "Device Settings" (in Log by... - every 0.2 seconds and fix every ~300ms).

Thanks.

‹ date filters seem not to work all the time can't connect to my iblue 747 or how many pins ›
Sat, 06/12/2010 - 11:41 — mdeweerd
mdeweerd's picture

You see these spikes when

You see these spikes when reception is worse or when you are not moving.

You can reduce them a lot by logging one of the HDOP, PDOP or VDOP and using the value to filter.  I use HDOP and set the upper limit to 1.4 (more or less, according to my observation).  That will remove most of them.

Further I once noticed that I had less spikes when I set the fix period to 500ms.  The fix period is the time between two position measurements.  The other log parameters can not have an effect on precision.  It is not proven as such that the fix period has an influence, but I think so.

So, in summary: log the HDOP value, set the limit to 1.4 in the filter settings, and set fix period to 500 ms. 

Sat, 06/12/2010 - 16:56 — gpsn00b
gpsn00b's picture

Thanks again for the

Thanks again for the informative response. I was filtering HDOP with the value of 1.96 (read on this forum or elsewhere). Slowly I am getting the results I want but it's a lot to experiment with :) Maybe you can enable "developer's settings" in BT747 that will load your own settings as a baseline for further adjustments. I know there's the "default" option but it doesn't enable all the stuff that you're writing about.

Cheers.

Sat, 06/12/2010 - 22:08 — mdeweerd
mdeweerd's picture

Hi This is the first time

Hi

This is the first time that somebody is asking to set my options - usually the request is the opposite ;-).  Your request is interesting but another button to add, explain, ... .  I'll keep it in mind and maybe one day it gets concrete.

The best HDOP value depends on your device - with my iBlue 747 I have to set 1.96, but the iblue 747 A+ has lower HDOP and there I set 1.4 and sometimes even less (1.1 or 1.2) - it depends on the device, the day, ... .

Sun, 06/13/2010 - 16:10 — gpsn00b
gpsn00b's picture

Well, maybe not a button but

Well, maybe not a button but an "A" in "FAQ" that deals with the settings. You've been doing this for a while and are a body of knowledge, so your settings would be great to start with rather than learn from scratch. Just my 2c.

Sun, 08/08/2010 - 09:25 — Anonymous (not verified)

Hello! I, too, did select

Hello!

I, too, did select "low" hdop/vdop values as suggested within this thread. But right now I have discovered that I thus "drop" valuable data. My current suggestion is to use

HDOP <= 2

VDOP <= 2.2

3 <= NSAT

My device is the "old" bt747 (i.e. NOT the +).

 

Regards, Michael

Sun, 08/08/2010 - 09:40 — mdeweerd
mdeweerd's picture

Thank you for the feedback.

Thank you for the feedback.  The value does indeed depend on your device - for the early iBlue 747 I use 1.9 or 1.95.