Geocaching Toolbox Inaccuracy

[+RaynPengi]

Like many I use the Geocaching Toolbox to help solve coordinate issues. However it was pointed out to me that the intersection of lines calculation gives a different answer to Cachesleuth. I contacted Cachesleuth who looked at it and claimed theirs was the more accurate. If you look at the Toolbox map the intersection pointer is not always right at the intersection. I then found a third website Geo.Javawa.nl which agreed with Cacheslueth. So what to do now?

[RuideAlmeida]

9 minutes ago, RaynPengi said:

So what to do now?

 

Did you asked on their website already?

[+fizzymagic]

3 hours ago, RaynPengi said:

Like many I use the Geocaching Toolbox to help solve coordinate issues. However it was pointed out to me that the intersection of lines calculation gives a different answer to Cachesleuth. I contacted Cachesleuth who looked at it and claimed theirs was the more accurate. If you look at the Toolbox map the intersection pointer is not always right at the intersection. I then found a third website Geo.Javawa.nl which agreed with Cacheslueth. So what to do now?

How much did they differ?

 

Since there is a quick-and-dirty method that uses a spherical approximation, I expect that one of the sites is using that.  If so, then that site is wrong. If you send me an example of the results I will be able to tell you which is correct, as I have written my own.

[+fizzymagic]

Well, I tested the two sites and I can confidently say that Geocaching Toolbox is incorrect.  By a surprising amount.  The Dutch site agrees exactly with my calculations.

 

Interestingly, the Geocaching Toolbox result is not the spherical-Earth approximation.  It is just wrong.

 

Data

Line 1: N 37 50.000 W 122 00.000 - N 37 00.000 W 121 00.000
Line 2: N 37 00.000 W 122 00.000 - N 37 50.000 W 121 00.000

High-accuracy
Intersection = N 37 25.203 W 121 30.000  (37.42004708, -121.50000000)
Residual = 2.85e-24  it=68
From N 37 50.000 W 122 00.000: Fwd = 316.255086  Rev = 135.949825
From N 37 00.000 W 122 00.000: Fwd = 223.744914  Rev = 43.442542

Spherical
Intersection = N 37 25.203 W 121 30.127  (37.42005687, -121.50211660)
Residual = 1.79e-23  it=68
From N 37 50.000 W 122 00.000: Fwd = 316.375194  Rev = 136.071226
From N 37 00.000 W 122 00.000: Fwd = 223.622234  Rev = 43.321141

Geocaching Toolbox answer: N37° 25.307' W121° 30.000' (off by almost 200 m!)

 

[+Hügh]

5 minutes ago, fizzymagic said:

It is just wrong.

Is Geocaching Toolbox by any chance doing a naive 2d Cartesian intersection?

[+RaynPengi]

Thanks for that. I checked the two point intersection and that seems to be ok on distance and coords but gives a different bearing?

 

What I do now is "assume" people are using toolbox to get the right answer but allow the Cachesleuth one in Geocheck as well. For new ones I will use Cachesleuth but put in a warning, though that does give the game away..