Re: Trying to locate a property marker using GPS


Chris Smolinski wrote:
I've been trying to locate a concrete property marker for some time now,
without luck, and wanted to see if I was going about it the right way.
According to the survey for my lot, there is supposed to be a concrete
marker at one of the back corners (I have a rather odd shaped 2 acre lot
with 9 sides). Unfortunately this marker is somewhere in the woods, in
an area filled with thick brambles, thorns, vines, etc. I'm trying to
clear out the brush, but want to know where I'm entitled to clear once I
start getting close to the property lines.

The survey shows the marker as being S 54 deg, 22', 0" E, 298.44 ft
from another corner point, which is close to my house and known.

So, I had the (maybe not so) bright idea of using a GPS receiver to try
to locate about where the marker should be. I understand that off the
shelf GPS receivers are not suitable for surveying, but my goal was not
to get a precise measurement, but within say 10 or 15 ft, so that I
would have a chance of finding the concrete marker. I'm using a GPS
receiver with a USB interface and WAAS, and some software I wrote to
average readings over several minutes, with a laptop. The first thing I
learned is that trees and leaves are not kind to GPS signals, and the
second thing is that trampling through the woods with a laptop and GPS
dongle isn't exactly fun. This might have to wait until fall when the
leaves are off the trees.

The survey has a arrow pointing North with the notation Mag North
2/1976, which I am assuming means that all of the bearings are
referenced to magnetic and not true north? From what I could find out,
for my location (76 deg 58 min East and 39 deg 42 min North) in 1976,
mangetic north was 8 degrees and 46 minutes West of true North. So the
bearing from the one point to the concrete marker (S 54 deg, 22', 0" E)
is really S 63 deg 8' 0" E, ref from true north, correct?

Since I don't have an absolute lon/lat location for any point on the
survey, I decided to take a GPS reading at the known point (OK, which
will introduce more error into my process) and then compute the lon/lat
location for the concrete marker. I ended up with an average position of
76 deg, 58 min, 28.066 sec W, 39 deg, 42 min, 15.960 sec N.

My understanding is that one second of latitude is 101.25 ft, and at my
latitude, one second of longitude is 78.1 ft.

Using simple trig, the 298.44 ft at that angle, the concrete marker,
bearing S 63 deg 8' 0" E is 266.2 ft east and 134.9 ft south of the
other point, or 3.408 seconds east and 1.332 seconds south of the point
at the other end of the line (76 deg, 58 min, 28.066 sec W, 39 deg, 42
min, 15.960 sec N), or located at 76 deg, 58 min, 24.658 sec W, 39 deg,
42 min, 14.628 sec N)

Any mistakes or bad assumptions with my above process? Needless to say
I didn't find the concrete marker. Before I try again, I want to make
sure I'm at least doing the calculations correctly, so I'm looking in
the right area. My hope is that with sufficient averaging I can get a
GPS location within 20 or so ft, which will let me find the marker.

Assuming this fails... what's the going rate for hiring a surveyor to
mark my property lines? ;-)

--
---
Chris Smolinski
Black Cat Systems
http://www.blackcatsystems.com

You must first determine the basis of North associated with your survey
plat. Some surveys permit an entirely random basis with no reference
to the controlling points. Many times such a survey will state
somewhere on the map that the directions are "Plat North" which means
they are only referenced to themselves. If this is true there is no
way to associate them to any real basis of north without calling a
surveyor.

.

Relevant Pages

  • Re: Trying to locate a property marker using GPS
    ... I had the bright idea of using a GPS receiver to try ... would have a chance of finding the concrete marker. ... The survey has a arrow pointing North with the notation Mag North ... mangetic north was 8 degrees and 46 minutes West of true North. ...
    (sci.engr.surveying)
  • Re: Trying to locate a property marker using GPS
    ... I had the bright idea of using a GPS receiver to try ... would have a chance of finding the concrete marker. ... The survey has a arrow pointing North with the notation Mag North ... mangetic north was 8 degrees and 46 minutes West of true North. ...
    (sci.engr.surveying)
  • Re: Trying to locate a property marker using GPS
    ... I had the bright idea of using a GPS receiver to try ... would have a chance of finding the concrete marker. ... The survey has a arrow pointing North with the notation Mag North ... mangetic north was 8 degrees and 46 minutes West of true North. ...
    (sci.engr.surveying)
  • Re: Trying to locate a property marker using GPS
    ... I had the bright idea of using a GPS receiver to try ... would have a chance of finding the concrete marker. ... The survey has a arrow pointing North with the notation Mag North ... You must first determine the basis of North associated with your survey ...
    (sci.engr.surveying)
  • Re: Roughtly converting DOP to metric error
    ... My cave survey freeware connects to a GPS for surface tracking. ... User Equivalent Range Error is computed in the tables lower on this page. ... Position error can range from tens of meters to a few millimeters (survey) depending on equipment, ...
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