A Little Research Doesn't Hurt

In the regular course of talking to people …  and trying to solve their problems, problems that are closer to my expertise than theirs … often means that I play around with some of the equipment that we occasionally sell but that aren’t part of our normal product lines. When I do this, the information that I derive often just sits on a shelf somewhere (apart from the copy in my head) until some of my tidier employees (or wife) clean them up … usually into the round file … so here it is for posterity !

Recently I was consulted on my expertise to potentially sell but first to test in real world conditions, several more or less competing GPS products. The key words here are “more or less”. Although I have used some of the products, I had not used all of them and really I had never used them in any comparative sense.

Well, as I dislike those who advise me and are absolutely wrong in their advice, I thought that I’d put myself in their shoes and do some proper comparisons to drop in their hands as an informed starting point.

The GPS they required had to communicate via Bluetooth (BT) and be able to give real time positions that were consistent in their accuracy and had to be, well, more precise than is practically possible … but really, they were looking for the best tool available. Now of course I have an opinion from collective experience but nothing that could be shown as empirical evidence.

The GPS that we had to compare were:

  1. The SXBlue II, a tried and true BT GPS engine that is popular in the forestry sector.
  2. The Dual XGPS160 which is a popular BT for iPads and pilots.
  3. The Arrow 100 which is a newly minted BT product built by the engineer of the SXBlue.

 

BT GPS Units

Here are the results of a non simultaneous test from my office that has a GPS wavelength repeater on the roof so the geographical (GPS) position does not move. I’ll use the running average as that is what will be available / used in the field.

The sample time length were similar at about 1000 seconds. The Dual produced more data (10 Hz vs. 1 Hz) but as you can see, that doesn’t make it better (as some might think) The GPS satellites only produce 1Hz data so anything more than that is simply a product of an algorithm (poor data in = poor data out).

You’ll notice that the averaged position of our antenna is quite similar, but averaging is seldom done in the real world, and certainly not for 1000 seconds. The key number here is the Standard Deviation in meters shown in brackets.

  1. SXBlue II:   N55* 10.6376 (1.253m)  W118* 47.7168 (1.030m)   Elevation: 667.54m (2.566m)
  2. Dual XGPS160: N55* 10.6403 (2.355m)  W118* 47.7142  (3.047m)  Elevation: 655.90m (2.419m)
  3. Arrow 100:   N55* 10.6376 (0.369m)  W118* 47.7170 (0.233m)   Elevation: 667.72m (0.632m)

 

If you look at this data graphically, this is what you see: BTW the visible grid = 1.68m

1)SXBlue                                              2) Dual                                                  3) Arrow

SXBlue GraphDual GraphArrow Graph

 

 

 

 

 

 

 

So it would appear that my recommendation of the Arrow 100 is definitely starting at the head of the pack. I’m confident that the Arrow 100 will be the GPS unit of choice for almost any field application in the future.

Some might say that we should have tested a Trimble GPS … I’ll leave that to others … they tend to boast but underperform and are overpriced (I don’t use them anymore).

If you’d like more information on my methods or the actual data … or how to do this yourself …

send me a line: rc@skybase.ca

 

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