Ultimate GPS Breakout Inaccurate

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wsen18
 
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Ultimate GPS Breakout Inaccurate

Post by wsen18 »

I purchased the GPS breakout a while back and am just getting around to using it. I set it up by following the Adafruit tutorial. Everything appeared to work, but after cross-checking the coordinates with multiple coordinate finding utilities online, I found that the coordinates from the GPS were off. It is considerably more than the 3 meter accuracy shown in the specifications. Is there anything i can do to fix this?

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Franklin97355
 
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Re: Ultimate GPS Breakout Inaccurate

Post by Franklin97355 »

Can you post some output from the serial monitor? Also are you inside or out?

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wsen18
 
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Re: Ultimate GPS Breakout Inaccurate

Post by wsen18 »

I was outside.
Attachments
GPS Serial Monitor Output.txt
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adafruit_support_mike
 
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Re: Ultimate GPS Breakout Inaccurate

Post by adafruit_support_mike »

There are two classes of error in GPS readings: precision errors (large jumps between readings from the same position) and position errors (consistent numbers that map to some other location).

I see one hiccup in the last reading, but the others seem to be fairly consistent. Which category of error are you seeing?

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wsen18
 
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Re: Ultimate GPS Breakout Inaccurate

Post by wsen18 »

There is a position error.

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adafruit_support_bill
 
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Re: Ultimate GPS Breakout Inaccurate

Post by adafruit_support_bill »

It would be helpful if you could be a little more specific. What is the difference between the position reported and what you believe to be the correct position?

Most 'position errors' are due to a misinterpretation of the data format.
https://learn.adafruit.com/adafruit-ult ... ter-wiring
People often get confused because the GPS is working but is "5 miles off" - this is because they are not parsing the lat/long data correctly. Despite appearances, the geolocation data is NOT in decimal degrees. It is in degrees and minutes in the following format: Latitude: DDMM.MMMM (The first two characters are the degrees.) Longitude: DDDMM.MMMM (The first three characters are the degrees.)

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jigawatt
 
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Re: Ultimate GPS Breakout Inaccurate

Post by jigawatt »

I'm getting inaccurate position readings too. It seems to be consistently off about a mile or two in the E-NE direction. Isn't the GPS Library code handling all the parsing of data? I'm creating new variables to store new corrected values for Long and Lat offset.

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adafruit_support_bill
 
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Re: Ultimate GPS Breakout Inaccurate

Post by adafruit_support_bill »

Please post an example of the errors you are seeing.

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jigawatt
 
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Re: Ultimate GPS Breakout Inaccurate

Post by jigawatt »

The example code I would post would look very similar to the guy before. The issue is that if I put coordinates in google earth, the position says on the map that I'm about 10-12 blocks away from where I actually am.

I read this:
People often get confused because the GPS is working but is "5 miles off" - this is because they are not parsing the lat/long data correctly. Despite appearances, the geolocation data is NOT in decimal degrees. It is in degrees and minutes in the following format: Latitude: DDMM.MMMM (The first two characters are the degrees.) Longitude: DDDMM.MMMM (The first three characters are the degrees.)

"this is because they are not parsing the lat/long data correctly." Isn't the parsing being handled in library code? The _.MMMM part is a little off. This is the value I'm offsetting the. I subtract something like .2500 for N and .0250 for W (I think, as I dont have the code in front of me... at work)

After looking at his closer I'm noticing this:

$GPGGA,051955.000,3000.5935,N,09532.2458,W
Location: 3000.0000N, 9532.2460W

$GPGGA,051957.000,3000.5935,N,09532.2458,W
Location: 3000.0002N, 9532.2460W

$GPGGA,051959.000,3000.5936,N,09532.2458,W
Location: 3000.0004N, 9532.2460W

$GPGGA,052001.000,3000.5938,N,09532.2459,W
Location: 3000.5937N, 9532.2460W

First three sets are off but looks like the last one printed correctly, Kinda wish he would have let it run a little longer :)

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adafruit_support_bill
 
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Re: Ultimate GPS Breakout Inaccurate

Post by adafruit_support_bill »

Post the GPS coordinates you are getting from the breakout and the coordinate you believe to be correct for your location.

Also check your Google Earth configuration. Google Earth supports a variety of coordinate formats. You may not have it configured for the Degrees/Decimal Minutes format that is standard for GPS.
https://support.google.com/earth/answer/148070?hl=en

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