GPS Waypoints From The Air

[packer58]

Here's my question. Your in a plane a few hundred feet above the ground surface "HOPEFULLY !!!!!" with your handheld GPS of choice. How accurate would the waypoints be. I'm well aware of how a GPS works by triangulation but don't know the affects on accuracy while in the air.

 

[packer58]

WOW........No pilots, everybody must be eating dinner

 

[hardstalk]

I did a quick google search (bored as €%^+ in a hotel room. Not trying to be a smarty pants) but guys seem to have had success with garmins in commercial planes.

 

[Ikeepitcold]

Ill get back to you on this. I have a few pilots in the family. Ill ask them.

 

[sab]

Latitude and Longitude are not affected by altitude. Think of a line drawn from the center of the earth through your waypoint. No matter what altitude you are at, your GPS will direct you to the point that the line intersects your altitude. In other words, it will always put you directly over the waypoint. Does that make sense?

Regards,
Scott

 

[JMSZ]

Your GPS should give you a figure of merit or accuracy - usually accuracy for civilian models. You are someplace within a sphere defined by that radius, whether you are on the ground or airborne.

Your greatest accuracy requires 3D, which in turn requires a minimum of 4 satellites, the more satellites you get, theoretically the more accurate your fix should be.

Now, if you are talking about marking waypoints from the air, the accuracy of those waypoints will depend on the accuracy of the GPS, how fast the aircraft the is moving, how fast you push the button and how fast the GPS reads the position and you push the button.

Your point could be off by a few hundred feet, but in most cases, it won't matter.

Now, if you're planning on navigating to a waypoint in the dark and there are cliffs around, I would advise against it .

 

[packer58]

Thanks guys for the input,

sab, i'm trying to make sense of your explanation of long and lat radiating from the center of the earth, I think...

JMSZ, I agree that pinpoint accuracy isn't a big deal, a few hundred feet would be more than adequate.

 

[JMSZ]

Thanks guys for the input,

sab, i'm trying to make sense of your explanation of long and lat radiating from the center of the earth, I think...

JMSZ, I agree that pinpoint accuracy isn't a big deal, a few hundred feet would be more than adequate.

What sab was saying is that the GPS system uses the center of the earth as the reference point to determine your position.

The GPS system doesn't use lat and long to determine where you are, it determines your location in space using the center of the earth as a reference. Think of a line starting at the center of the earth and going to and through your position or your waypoint.

That line points to a position in space that the system then associates with a specific latitude and longitude. Your elevation is a point on that line that is determined by the distance from the center of the earth to that point minus the distance to the center of the earth and sea level.

 

[Caseyu]

It can be very accurate. it also can be the exact opposite depends on your pilot calling out mark or how good you are on guessing you are above the exact spot. And from plenty years of experience marking fires from above it takes some practice!!! you should be able to get close enough to slip in the spot though

 

[wolftalonID]

I would agree. As a pilot, I use GPS all the time and always find the spot. However I already have the coordinates to search for. Finding a spot from the air is not as easy as from the ground because the visual ques are totally different. If you know it from the ground, it's hard to find it sometimes, from the air. If you know it only from the air, ground references are going to look different when you are on the ground.

Gps is GPS. The coordinates are always that. Learning exactly what straight down it for marking a location is going to take practice. I suggest you go, then at home pull up the marks on google earth. Then tweak the inputs on your handheld by what you see.
For example you mark 15w 12s and when you see it on the satellite and it shows 14 w 11 s then correct to what google earth shows for more accuracy. My examples are just simple numbers for effect not actual coordinates.

You will find this much more helpful as google earth is spot on 99% of the time and your first attempt at fly by spot marking will not be. So also being you are probably going to overfly an area of your choice, use google earth to develop some coordinates to send the pilot to. Then add to them as your there by marking those of interest or crossing off those you already have if its not what your looking for.

 

[packer58]

Thanks again guys for the help, I planned on putting together a list of coordinates generated from Google Earth scouting and having the pilot fly over them. I'll be flying as a second passenger with another EF member over his Nevada unit.