Coordinate precision

[+Team_Bunnies]

Hello,

 

I'm wondering about what exactly the coordinates are telling me. Since they represent a grid on the globe, how big is the "rectangle" described with the usual notation ( Degree minutes.xxx)?

Of course there's also the issue of GPS signal precision, but that's not what I mean here. Thanks for any insights!

 

[+barefootjeff]

38 minutes ago, Team_Bunnies said:

Hello,

 

I'm wondering about what exactly the coordinates are telling me. Since they represent a grid on the globe, how big is the "rectangle" described with the usual notation ( Degree minutes.xxx)?

Of course there's also the issue of GPS signal precision, but that's not what I mean here. Thanks for any insights!

 

 

One thousandth of a minute in latitude corresponds to about 1.85 metres on the ground, while for longitude it will vary from 1.85 metres at the equator down to zero at the poles.

[+niraD]

49 minutes ago, barefootjeff said:

One thousandth of a minute in latitude corresponds to about 1.85 metres on the ground, while for longitude it will vary from 1.85 metres at the equator down to zero at the poles.

Meanwhile, under ideal conditions, a consumer GPSr will be accurate to about 3m (10ft). That applies both to your device, and to the cache owner’s device, so you may find the container 5-6m (16-20ft) from ground zero under ideal conditions. Under less than ideal conditions, both GPSr readings can be much less accurate. Once you get within that distance of ground zero, put your device away and look around for places where a container could be hidden.

[+Max and 99]

4 hours ago, Team_Bunnies said:

Hello,

 

I'm wondering about what exactly the coordinates are telling me. Since they represent a grid on the globe, how big is the "rectangle" described with the usual notation ( Degree minutes.xxx)?

Of course there's also the issue of GPS signal precision, but that's not what I mean here. Thanks for any insights!

 

If I understand correctly.... where I live, a change in the last digit of north is about 6 feet, and a change in the last digit of west is about 4.5 feet. The smallest rectangle would be 4.5 feet times 6 feet, or approximately 27 square feet.  Is that what you are asking?

[+ras_oscar]

On the other hand, if you are asking how far from the posted cords to perform your search, I usually don't go more than 30 feet in all directions. Of course, last weekend I did log a find on a cache that read 60 feet fro the posted coordinates.l

[+Seeker_Knight]

To help you understand a bit better..
You are not talking about perfect rectangular shapes, but rather more of a trapezoid of sorts. This is because the point of reference is roughly the equator, with the trapezoid continually getting smaller for each additional degree as you approach the North and South poles. There is also consideration in the results for the fact that you are never at the same elevation as the datum baseline, compounded by the fact that the Earth is not a perfect sphere. Then there is the fact that all sides are not lines, but arcs, albeit with very very tiny deflections per foot.
Add to this the environmental conditions, and it is amazing these devices can come as close as they do. When I was a land surveyor, we had to enter a lot of variables into the equipment such as temperature, humidity, visibility, elevation etc., but we were able to get readings to within an area the size of a quarter or even closer. One of our crews took the instruments out for a Public Works Dept demonstration at a local event sponsored by the local government. They created a grid with one inch squares, each having a unique number and in total, covering an area the size of a parking space for a car. They would have the participants walk over the area and write down a number for the spot they chose. Then the operator would come out of the building and locate the exact box they had chosen. He got every single one of them for the entire day that they were out there. Had to be hundreds of them in all. But you are also talking about a piece of equipment that cost well over $100,000 at the time, and a team of men with 50years combined experience in land surveying. These were the guys who set the datum which private land surveyors base there work on, including important and valuable property line work. I'm pretty sure you can get setup with a station as a private citizen, but not many people have either the finances, nor the need of that level of accuracy.
So we go out in all kinds of weather conditions, constantly changing and variable cloud cover, tree canopy cover, building and structure impediment, and a much less expensive tool set and experience level and just learn to adjust accordingly. Also remember that there is a combination of errors (both compounding and compensating) introduced by not only your unit and level of experience, but also that of the operator who set the coordinates initially.
Somewhat of a miracle that we ever find any of these little devils.

Seeker-Knight

Edited January 30, 2020 by Seeker_Knight
Gramer and punctuation

[+Team_Bunnies]

On 1/27/2020 at 1:50 AM, Max and 99 said:

If I understand correctly.... where I live, a change in the last digit of north is about 6 feet, and a change in the last digit of west is about 4.5 feet. The smallest rectangle would be 4.5 feet times 6 feet, or approximately 27 square feet.  Is that what you are asking?

Yes, that's precicely what I meant. We're based in Central Europe (Southern Germany),  so if you're in North America our "rectangle" would be slightly smaller, right? So roughly 1.2  meters x 1.8 meters?

Thanks a lot

Edited February 2, 2020 by Team_Bunnies

[+Seeker_Knight]

2 hours ago, Team_Bunnies said:

Yes, that's precicely what I meant. We're based in Central Europe (Southern Germany),  so if you're in North America our "rectangle" would be slightly smaller, right? So roughly 1.2  meters x 1.8 meters?

Thanks a lot

 

I think you have a good grasp on the idea. These grid systems are a lot more complex than most people know. If you really want to get your head spinning, sit down with a licensed Engineer or Land Surveyor with a lot of experience. They'll take you on a trip through some mathematics that will make your head spin. LOL

Seeker_Knight