SparkFun Forums

[roppetty]

I'm looking at GPS modules to make a data aquisition system for a vehicle on a track and came across the EB-85A module. Seems to have pretty good accuracy, what I'm doing needs to have it be pretty accurate. I've read some similar products and they mention that their GPS modules have a 3m accuracy, but on a track, where areas are wide open and a wide view of the sky, they claim 1m. I'm hoping this is true and this unit will show similar characteristics.

One thing I was concerned with though is this unit doesn't have an external antenna. Maybe the SF photos don't show it, but I'm guessing the antenna is built into the module rather than being plugged into it? I'm concerned about the accuracy with it being mounted inside the car. I'm thinking it'll be on the dash, so it will have visibility through a windshield, but i'd really like to have an external antenna and mount it on the roof of the vehicle for the best possible locks.

I'm assuming the SirfIII units won't get the accuracy I'm looking for? I see the EM-408 has a connector for external antenna, but even with WAAS it says it only gets 5m.

I was also looking at some of the ublox modules, but there isn't as much data on people using them as there is with the units here. can anyone offer any advice that have used any of these modules? I've never done gps before, just trying to hopefully get it right the first time without wasting money.

[septer012]

the E85A is accurate within 7.6 feet with WAAS. 2.3 Feet with DGPS.

[etracer]

I don't know where you're getting those accuracy numbers. All of the documentation published by the manufacture lists the accuracy at 3.3 meters or 2.6 meters with DGPS. That's quite a bit more than 2.3 feet.

You're not going to find a non-military GPS with 2.3 foot accuracy.

[septer012]

I read a review online with a comparison of gps modules to a known point position...

and it pulled those impressive numbers, I agree though, that was a single case.

[scalegps]

All GPS accuracy figures have to be taken with a grain of salt. If the manufacturer is quoting 1 Sigma numbers, the accuracy quoted is only attained 68% of the time. Once you get past all the marketing jibberish current WAAS/SBAS enabled receivers have pretty much the same performance. Physics trumps marketing every time.

Where you can see a difference is in how the manufacturer has implements the Kalman and other proprietary filters. Some of the receivers allow you to change filter settings through the serial port to match your application. I used to be a GPS distributor apps engineer, and people were always really impressed with the position stability of the Sony receivers. Their position stability was great (<1m most of the time), but the price you paid was response time to a change in position/velocity. So long as you are driving in a car it is not an issue, but if your position is changing rapidly and in different directions the lag was noticeable.