MapSource bearings

[+White King]

I use MapSource software for plotting up my caching. I also have an eTrex Vista HCx. Sometimes one is required to make a projection from one cache to another location. My question is: as the bearing value changes from (say) 90 degrees to 91 degrees (either in the software or on the eTrex), what is the actual bearing at the point of change? i.e. is it in this case 91 degrees or is it 90.5 degrees (due to display rounding)? This makes a 0.5 degree difference in the construction, which can put the location off by quite a bit.

 

Thanks,

 

White King

[+H2OBob]

I assume you are talking about projecting a waypoint, which is sometimes used to make the cache harder to find by muggles. I'm not familiar with the Vista HCx, but on my Legend C, you input the direction and distance, and it projects the waypoint, then you "goto" that waypoint. the direction shouldn't change. I hope this helps. Maybe I'm off course a little.

[+White King]

I assume you are talking about projecting a waypoint, which is sometimes used to make the cache harder to find by muggles. I'm not familiar with the Vista HCx, but on my Legend C, you input the direction and distance, and it projects the waypoint, then you "goto" that waypoint. the direction shouldn't change. I hope this helps. Maybe I'm off course a little.

 

Thanks for your reply.

 

Off course just a little . I know how to make the projection, but both the s/w and the GPS only work in whole degrees. As you move the mouse over the map (in MapSource) the bearing changes from one value to the next. My question is: what is the bearing value at the point where it changes? Normally software is set up to round decimals up, so once the bearing reaches (say) 90.5 degrees the s/w would show 91 degrees. This 0.5 degree error can make a substantial difference when projecting over several miles, but if one knows how the s/w works one can compensate.

 

So, I'm wondering if anyone knows what MapSource is coded to do.

 

Projecting from the handheld GPS is tricky at best, so although the same question applies in theory it's probably academic .

 

White King

[+Prime Suspect]

MapSource = wrong tool for the job

GeoCalc = right tool for the job

[+H2OBob]

OK, I see what you mean. I don't think that Garmin intends mapsource to be used at that accuracy. The best distance /heading numbers that I could ever get, were when marking two waypoints, then using the distance/heading tool to get the info. You still only get whole degrees, though, so if it says 30 degrees, it could be anywhere between 29.5 and 30.5, assuming that it rounds at the.5 point. Also, consider that the distance is rounded to the nearest tenth of a mile, so you could be nearly a tenth of a mile off there, as well. You might fire off an email to garmin. they might be able to tell you more. Maybe someone else has has an idea.

[gallet]

It doesn't matter how accurate you are if the person who made the original projection did not use the same level of accuracy, surely?

[+edscott]

It doesn't matter how accurate you are if the person who made the original projection did not use the same level of accuracy, surely?

 

Just as the GPSr gets uneasy about caches hidden with a map and compass, I would be uneasy about a projection made with only a GPS. A simple $15 compass will do this job.

[+StarBrand]

MapSource = wrong tool for the job

GeoCalc = right tool for the job

Agreed - best way to do a projection calculation for anything over a hundred feet.

[+Alan2]

It doesn't matter how accurate you are if the person who made the original projection did not use the same level of accuracy, surely?

 

Just as the GPSr gets uneasy about caches hidden with a map and compass, I would be uneasy about a projection made with only a GPS. A simple $15 compass will do this job.

 

What is the accuracy of a $15 compass? What is the accuracy of a GPS with on-board compass? I've compared the reading on my old Vista with on-board compass and it reads the same as my $49 Suunto base plate compass and both are probably at least a degree inaccurate. (What's the accuracy of the newer Vista HCx?) I would agree with your statement if you have a GPS without on-board compass.

 

The bottom line is that the GPS is inaccurate as to your current location and projected location by 10-20 feet anyway. Then the compasses (no matter what type you use) are a degree off. Add the fact the the hider or the finder if you're the hider is using different equipment with its own inaccuracies. Getting fractions of degrees is moot.

[+White King]

It doesn't matter how accurate you are if the person who made the original projection did not use the same level of accuracy, surely?

 

Just as the GPSr gets uneasy about caches hidden with a map and compass, I would be uneasy about a projection made with only a GPS. A simple $15 compass will do this job.

 

What is the accuracy of a $15 compass? What is the accuracy of a GPS with on-board compass? I've compared the reading on my old Vista with on-board compass and it reads the same as my $49 Suunto base plate compass and both are probably at least a degree inaccurate. (What's the accuracy of the newer Vista HCx?) I would agree with your statement if you have a GPS without on-board compass.

 

The bottom line is that the GPS is inaccurate as to your current location and projected location by 10-20 feet anyway. Then the compasses (no matter what type you use) are a degree off. Add the fact the the hider or the finder if you're the hider is using different equipment with its own inaccuracies. Getting fractions of degrees is moot.

 

I'd like to thank all the above for their practical input and perspectives. I could not agree more with what appears to be the general consensus - you really can't get there from here because you don't know exactly where here is and you have no idea where the hider thought there was (or how they measured it), and even if you did the tools just aren't accurate enough anyway. [i'd really like to know how the hider projected by decimal degrees over a distance of 5 miles in this case.] However, while feeling the question was a bit academic, I wanted to get some other persectives.

 

The cache involved is a multi cache almost entirely consisting of projections of around 10 km (~6 miles for the metrically challenged) . For the first waypoint the projected position using MapSource and my assumption of decimal rounding got to within 20 m of the 'actual' location as determined by my GPS unit. I was trying to improve on that . Guess we'll see what happens with wp 2.

 

Thanks for the tip about GeoCalc.

 

Compass accuracy on the Vista - don't know. How would you find that out? Maybe Garmin has it in the specs but I haven't seen it

 

Thanks again,

 

White King

[+Alan2]

[i'd really like to know how the hider projected by decimal degrees over a distance of 5 miles in this case.]

 

Well, the search teams are still looking for the cachers who are still looking for that cache

[+Prime Suspect]

I'd really like to know how the hider projected by decimal degrees over a distance of 5 miles in this case.]

GeoCalc?

[+White King]

I'd really like to know how the hider projected by decimal degrees over a distance of 5 miles in this case.]

GeoCalc?

 

And probably 'backwards' as well - log the actual locations as 'accurately' as possible and enter the coords into GeoCalc and have it compute distance and bearing. Using GeoCalc (thanks for that tip) I was able to project waypoints that were within 3-4 metres of where I actually logged the cache. So this multi cache requires a laptop as well as the GPS! BTW, I find GSAK a good tool as well. It seems to project as well as GeoCalc and also has the cache data base capability.