- Joined
- May 2, 2001
- Messages
- 7,490
GPS and/or topo maps for ranging
--------------------------------------------------------------------------------
Anyone out there with experience or practical knowledge on the use of the civilian GPS unit and/or topo maps for determining range.
I've been toying with the idea of recording the coordinates of various known 'hot' spots onto my library of topo maps. I figure the GPS can get me a 'fix' to within 10 yards and that if I know the sites the animals present in I can use the previously recorded position of the animal and my current position to get a line-of-sight distance. I don't need to worry about the functioning of the laser unit and the distance for fixes on the GPS are not limited to 1000 yards or so.
Any thoughts?
posted April 13, 2001 08:00 AM
Warren Jensen
Member
From: Arco, ID US
Registered: April 12, 2001
Posts: 16
GPS for ranging.
--------------------------------------------------------------------------------
With the GPS units that I have used, and my experience is not extensive by any means, it is possible to get different location readings for the same place on different days. It is usually not a great difference and is probably a function of which and how many satellites you are receiving at that time.
I would be real interested in how this works out for you Dave. I have had some ideas along these lines myself, but have not had the opportunity to pursue it.
[email protected] http://www.lostriverballistic.com
posted April 13, 2001 04:00 PM
Ken Howell
Member
From: Stevensville, Montana
Registered: April 12, 2001
Posts: 5
When my son was using the GPS in surveying Forest Service lands here several years ago, I asked his boss — surveyor for the Bitterroot National Forest — how accurate GPS surveying was. I was especially interested in its distance-measuring accuracy, having been "brought up" on the 66-foot steel chain and disappointed in my one use of stadia in the Arctic.
His answer was that GPS was VERY accurate (I forget the error level) in measuring the distance from Point A to Point B but not nearly so accurate in establishing where either point was, relative to the rest of the world.
I can not guess whether this tells you anything useful. I'm not a bit familiar with either GPS as used with the instruments for land-surveying or GPS as used with the hand-held doodads available to ordinary citizens.
I'd check this out with some up-to-date surveyor
posted April 13, 2001 06:29 PM
Len Backus
Administrator
From: Oshkosh, WI
Registered: April 10, 2001
Posts: 21
GPS
--------------------------------------------------------------------------------
Since last year on 5/1/00 "selective availablity" has been turned off. This was a Department of Defense built-in random error.
Warren, now the expected accuracy is supposed to be in the range of 10 to 20 yards. Have you tried your repeated tests since that date?
I sold my GPS about 4 years ago when I figured out in the field how variable the reading for a specific location was. Now that SA is turned off I may purchase one again.
Len Backus
posted April 13, 2001 06:37 PM
Warren Jensen
Member
From: Arco, ID US
Registered: April 12, 2001
Posts: 16
GPS
--------------------------------------------------------------------------------
No, I haven't tried the repeatability test since then. I will, and good point Len.
[email protected] http://www.lostriverballistic.com
posted April 16, 2001 07:53 AM
--------------------------------------------------------------------------------
Anyone out there with experience or practical knowledge on the use of the civilian GPS unit and/or topo maps for determining range.
I've been toying with the idea of recording the coordinates of various known 'hot' spots onto my library of topo maps. I figure the GPS can get me a 'fix' to within 10 yards and that if I know the sites the animals present in I can use the previously recorded position of the animal and my current position to get a line-of-sight distance. I don't need to worry about the functioning of the laser unit and the distance for fixes on the GPS are not limited to 1000 yards or so.
Any thoughts?
posted April 13, 2001 08:00 AM
Warren Jensen
Member
From: Arco, ID US
Registered: April 12, 2001
Posts: 16
GPS for ranging.
--------------------------------------------------------------------------------
With the GPS units that I have used, and my experience is not extensive by any means, it is possible to get different location readings for the same place on different days. It is usually not a great difference and is probably a function of which and how many satellites you are receiving at that time.
I would be real interested in how this works out for you Dave. I have had some ideas along these lines myself, but have not had the opportunity to pursue it.
[email protected] http://www.lostriverballistic.com
posted April 13, 2001 04:00 PM
Ken Howell
Member
From: Stevensville, Montana
Registered: April 12, 2001
Posts: 5
When my son was using the GPS in surveying Forest Service lands here several years ago, I asked his boss — surveyor for the Bitterroot National Forest — how accurate GPS surveying was. I was especially interested in its distance-measuring accuracy, having been "brought up" on the 66-foot steel chain and disappointed in my one use of stadia in the Arctic.
His answer was that GPS was VERY accurate (I forget the error level) in measuring the distance from Point A to Point B but not nearly so accurate in establishing where either point was, relative to the rest of the world.
I can not guess whether this tells you anything useful. I'm not a bit familiar with either GPS as used with the instruments for land-surveying or GPS as used with the hand-held doodads available to ordinary citizens.
I'd check this out with some up-to-date surveyor
posted April 13, 2001 06:29 PM
Len Backus
Administrator
From: Oshkosh, WI
Registered: April 10, 2001
Posts: 21
GPS
--------------------------------------------------------------------------------
Since last year on 5/1/00 "selective availablity" has been turned off. This was a Department of Defense built-in random error.
Warren, now the expected accuracy is supposed to be in the range of 10 to 20 yards. Have you tried your repeated tests since that date?
I sold my GPS about 4 years ago when I figured out in the field how variable the reading for a specific location was. Now that SA is turned off I may purchase one again.
Len Backus
posted April 13, 2001 06:37 PM
Warren Jensen
Member
From: Arco, ID US
Registered: April 12, 2001
Posts: 16
GPS
--------------------------------------------------------------------------------
No, I haven't tried the repeatability test since then. I will, and good point Len.
[email protected] http://www.lostriverballistic.com
posted April 16, 2001 07:53 AM