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Who knows about GPS antennas?...

S

server

Guest
I have been looking online but there seems to be, for a lot of the
antennas, an assumption of prior knowledge. That I don\'t have.
What I want to do is survey some of my property line. Mainly so I
know about where it is because about 25% of the length is ambiguous.
I can pay a surveyor to do the job but it would cost about 4
thousand bucks. Of course a proper survey would be more accurate and
precise but I don\'t need that accuracy or precision.
So I am looking for an antenna that could be either plugged into a
handheld GPS or a tablet. And I don\'t know even where to start. I
don\'t know how much gain I need. Or sensitivity. Maybe there is
already a han held unit that is good enough all by itself.
Our property is heavily wooded with a mix of conifers and deciduous
trees, mostly alders. In the summer the trees make my hand held GPS
unit useless. It is an older unit so I will be buying a modern one
that will hopefully be better.
I live north of Seattle and the satellites seem to be mostly in the
southern sky, if that makes any difference to any antennas.
I would like to keep the total expenditure for antenna and GPS unit
to less than $400.00
I have looked into renting a surveyors GPS unit but have not been
able to find anyone in the greater area who rents them.
Can anybody help?
Thanks,
Eric
 
J

Jeff Liebermann

Guest
On Sun, 09 Aug 2020 15:41:09 -0700, etpm@whidbey.com wrote:

I have been looking online but there seems to be, for a lot of the
antennas, an assumption of prior knowledge. That I don\'t have.
Yep. The basic assumption is that the user knows the difference
between a GPS receiver and a GPS antenna.

What I want to do is survey some of my property line. Mainly so I
know about where it is because about 25% of the length is ambiguous.
There are numerous Android applications useful for surveying. I use
\"Mobile Topographer\" (free) for accurately locating antenna towers for
generating coverage maps:
<https://play.google.com/store/apps/details?id=gr.stasta.mobiletopographer>
<http://applicality.com/projects/mobile-topographer-free/>
Basically, the way these work is to place the phone at a given
location and run the program for some length of time. The program
then averages many GPS position reports producing improved accuracy.
The longer it runs, the more accurate the position. This is an
alternative to using DGPS (differential GPS) correction data to post
process recorded positions, which is what the surveyors normally
provide.

For fun, I just fired up the program inside my house on my desk next
to a large picture window, which is not a great location for
surveying. On startup, it settled down to 12.0 meter accuracy. After
about 15 mins running, accuracy improved to 1.84 meters.

The problem with using averaging is that if your property boundary
position involves a court or planning department case, they are
unlikely to accept your amateur surveying as accurate. They want data
from a licensed surveyor that includes corrections from existing
benchmarks to deal with ground slipage, earthquakes, and continental
drift. If your county has online GIS data available, you can see the
type of maps that the county might be expecting. What the smartphone
GPS and averaging method buys you is a trial run to determine if it\'s
worth paying for a professional survey and whether you will have a
chance before a court or board. If there\'s a dispute with a neighbor,
it might also be sufficient to convince the neighbor to cooperate.

If you decide to go this route, make sure you use a fairly up to date
smartphone that can do GPS, WAAS, GLONASS, and possibly other
satellite navigation satellite systems. The more satellites, the more
accurate your position.

Altitude accuracy can be marginal depending on your location. For
example, if you\'re measuring the surveying the bottom of a canyon,
you\'ll have problems.

If you\'re doing to spend an afternoon doing this, you\'ll find that the
GPS can really run the smartphone battery down. I suggest having one
of the larger battery banks or 12V charger available.

Make sure you use the correct datum. WGS84 is the most common, but
there are still people who want NAD27.

There are YouTube videos on surveying with a smartphone:
<https://www.youtube.com/results?search_query=android+surveying+app>
and other apps that might be more suitable:
<https://www.google.com/search?q=android+surveying+applications>

If you want to do averaging with a laptop and an external (USB or
serial) connected GPS, look at software from:
<https://www.visualgps.net>
I use Visual GPS View ($5) and Visual GPS Legacy (free), which will
both generate a location plot, which you can then eyeball for a more
accurate position.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
S

server

Guest
On Sun, 09 Aug 2020 18:00:26 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Sun, 09 Aug 2020 15:41:09 -0700, etpm@whidbey.com wrote:

I have been looking online but there seems to be, for a lot of the
antennas, an assumption of prior knowledge. That I don\'t have.

Yep. The basic assumption is that the user knows the difference
between a GPS receiver and a GPS antenna.

What I want to do is survey some of my property line. Mainly so I
know about where it is because about 25% of the length is ambiguous.

There are numerous Android applications useful for surveying. I use
\"Mobile Topographer\" (free) for accurately locating antenna towers for
generating coverage maps:
https://play.google.com/store/apps/details?id=gr.stasta.mobiletopographer
http://applicality.com/projects/mobile-topographer-free/
Basically, the way these work is to place the phone at a given
location and run the program for some length of time. The program
then averages many GPS position reports producing improved accuracy.
The longer it runs, the more accurate the position. This is an
alternative to using DGPS (differential GPS) correction data to post
process recorded positions, which is what the surveyors normally
provide.

For fun, I just fired up the program inside my house on my desk next
to a large picture window, which is not a great location for
surveying. On startup, it settled down to 12.0 meter accuracy. After
about 15 mins running, accuracy improved to 1.84 meters.

The problem with using averaging is that if your property boundary
position involves a court or planning department case, they are
unlikely to accept your amateur surveying as accurate. They want data
from a licensed surveyor that includes corrections from existing
benchmarks to deal with ground slipage, earthquakes, and continental
drift. If your county has online GIS data available, you can see the
type of maps that the county might be expecting. What the smartphone
GPS and averaging method buys you is a trial run to determine if it\'s
worth paying for a professional survey and whether you will have a
chance before a court or board. If there\'s a dispute with a neighbor,
it might also be sufficient to convince the neighbor to cooperate.

If you decide to go this route, make sure you use a fairly up to date
smartphone that can do GPS, WAAS, GLONASS, and possibly other
satellite navigation satellite systems. The more satellites, the more
accurate your position.

Altitude accuracy can be marginal depending on your location. For
example, if you\'re measuring the surveying the bottom of a canyon,
you\'ll have problems.

If you\'re doing to spend an afternoon doing this, you\'ll find that the
GPS can really run the smartphone battery down. I suggest having one
of the larger battery banks or 12V charger available.

Make sure you use the correct datum. WGS84 is the most common, but
there are still people who want NAD27.

There are YouTube videos on surveying with a smartphone:
https://www.youtube.com/results?search_query=android+surveying+app
and other apps that might be more suitable:
https://www.google.com/search?q=android+surveying+applications

If you want to do averaging with a laptop and an external (USB or
serial) connected GPS, look at software from:
https://www.visualgps.net
I use Visual GPS View ($5) and Visual GPS Legacy (free), which will
both generate a location plot, which you can then eyeball for a more
accurate position.
Thanks for all the great info Jeff. This surveying I want to do is
not for legal reasons, mainly to just make sure I know where some of
the property line probably is and where a corner marker should be.
I have seen the corner marker but it may now be under a fallen tree.
A big hemlock that tipped over, as they tend to do, and the marker is,
I think, under the root mass or under the trunk right where it is the
largest, next to the root mass.
I do have one thing in my favor, and that is a monument at the end
of my road that marks one corner of my property. So I could do as you
say and check its location with my GPS. Then I will know how far off
my measurement is after doing as you suggest. But only at that one
place.
Eric
 
J

Jeff Liebermann

Guest
On Mon, 10 Aug 2020 10:00:50 -0700, etpm@whidbey.com wrote:

Thanks for all the great info Jeff. This surveying I want to do is
not for legal reasons, mainly to just make sure I know where some of
the property line probably is and where a corner marker should be.
I have seen the corner marker but it may now be under a fallen tree.
A big hemlock that tipped over, as they tend to do, and the marker is,
I think, under the root mass or under the trunk right where it is the
largest, next to the root mass.
In this area, as soon as the surveyors are done, the locals like to
move the markers to a location that favors their property. Two of my
neighbors were having a dispute over a lot line adjustment. They paid
a professional surveyor to survey the property. I was home at the
time and watched them work. I then photographed the location of all
the markers because two of them were one side of my property. Two
days later, the markers had all moved. I\'ll spare you the rest of the
fiasco. At one point, I used a smartphone and Mobile Topographer Free
to demonstrate that the markers had been moved, which mostly solved
the problem.

I do have one thing in my favor, and that is a monument at the end
of my road that marks one corner of my property. So I could do as you
say and check its location with my GPS. Then I will know how far off
my measurement is after doing as you suggest. But only at that one
place.
You need at least two benchmarks to establish a point. Even if you
use a GPS, you will still need to account for ground movement using
the markers. In 1989, we had an earthquake, which moved things.
<https://www.conservation.ca.gov/cgs/earthquakes/loma-prieta>
The Pacific plate moved 6.2 feet to the northwest and
4.3 feet upward over the North American plate during
Loma Prieta.
Land west of the fault has been moving to the northwest
relative to land on the east at an average rate of 2 inches
per year for millions of year.

Since the GPS satellites did NOT move during the earthquake, a 6 ft
error makes surveying a bit of a challenge. The local benchmarks were
installed when the area was first subdivided into vacation tent sites
in about 1926. That would be about a 320 ft discrepancy between the
current GPS location and the 1926 survey marker. I somewhat verified
this about 5 years ago when I found a 200 ft discrepancy, but have
never bothered to ask the county how they handle such things. Since
most everything on the ground moves together, my guess(tm) is that the
county uses the surveyed benchmarks, and NOT the GPS location.
Depending on the age of your monument, you may have the same problem.
Ask your county how they handle ground movement.

This might help
<https://gis.santacruzcounty.us/DPWScans/recordmaps/100M39.pdf>
It\'s a 2001 survey of the property across the road from my house. Note
the copious use of found markers on the map as the \"basis for
bearings\". My guess(tm) is that they\'re trying to reconcile their
positions with that of the original 1926 sub-division map:
<https://gis.santacruzcounty.us/DPWScans/recordmaps/024M02.pdf>
without ever referring to GPS derived positions. If true, that will
make using GPS locations rather difficult. You will need two or more
monuments or benchmarks to adjust the property marker locations. The
2001 survey above used 7 markers.

Good luck with the project.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
S

server

Guest
On Mon, 10 Aug 2020 10:42:17 -0700, Jeff Liebermann <jeffl@cruzio.com>
wrote:

On Mon, 10 Aug 2020 10:00:50 -0700, etpm@whidbey.com wrote:

Thanks for all the great info Jeff. This surveying I want to do is
not for legal reasons, mainly to just make sure I know where some of
the property line probably is and where a corner marker should be.
I have seen the corner marker but it may now be under a fallen tree.
A big hemlock that tipped over, as they tend to do, and the marker is,
I think, under the root mass or under the trunk right where it is the
largest, next to the root mass.

In this area, as soon as the surveyors are done, the locals like to
move the markers to a location that favors their property. Two of my
neighbors were having a dispute over a lot line adjustment. They paid
a professional surveyor to survey the property. I was home at the
time and watched them work. I then photographed the location of all
the markers because two of them were one side of my property. Two
days later, the markers had all moved. I\'ll spare you the rest of the
fiasco. At one point, I used a smartphone and Mobile Topographer Free
to demonstrate that the markers had been moved, which mostly solved
the problem.

I do have one thing in my favor, and that is a monument at the end
of my road that marks one corner of my property. So I could do as you
say and check its location with my GPS. Then I will know how far off
my measurement is after doing as you suggest. But only at that one
place.

You need at least two benchmarks to establish a point. Even if you
use a GPS, you will still need to account for ground movement using
the markers. In 1989, we had an earthquake, which moved things.
https://www.conservation.ca.gov/cgs/earthquakes/loma-prieta
The Pacific plate moved 6.2 feet to the northwest and
4.3 feet upward over the North American plate during
Loma Prieta.
Land west of the fault has been moving to the northwest
relative to land on the east at an average rate of 2 inches
per year for millions of year.

Since the GPS satellites did NOT move during the earthquake, a 6 ft
error makes surveying a bit of a challenge. The local benchmarks were
installed when the area was first subdivided into vacation tent sites
in about 1926. That would be about a 320 ft discrepancy between the
current GPS location and the 1926 survey marker. I somewhat verified
this about 5 years ago when I found a 200 ft discrepancy, but have
never bothered to ask the county how they handle such things. Since
most everything on the ground moves together, my guess(tm) is that the
county uses the surveyed benchmarks, and NOT the GPS location.
Depending on the age of your monument, you may have the same problem.
Ask your county how they handle ground movement.

This might help
https://gis.santacruzcounty.us/DPWScans/recordmaps/100M39.pdf
It\'s a 2001 survey of the property across the road from my house. Note
the copious use of found markers on the map as the \"basis for
bearings\". My guess(tm) is that they\'re trying to reconcile their
positions with that of the original 1926 sub-division map:
https://gis.santacruzcounty.us/DPWScans/recordmaps/024M02.pdf
without ever referring to GPS derived positions. If true, that will
make using GPS locations rather difficult. You will need two or more
monuments or benchmarks to adjust the property marker locations. The
2001 survey above used 7 markers.

Good luck with the project.
Yeah, I didn\'t consider the monument moving. I live practically on top
of the South Whidbey Fault and there is motion associated with both
the fault and the whole region. The plate Whidbey is on is rotating
clockwise and just a few miles from me the island is moving a couple
millimeters per year.
Thanks Again,
Eric
 
J

Jeff Liebermann

Guest
On Mon, 10 Aug 2020 10:56:59 -0700, etpm@whidbey.com wrote:

Yeah, I didn\'t consider the monument moving. I live practically on top
of the South Whidbey Fault and there is motion associated with both
the fault and the whole region. The plate Whidbey is on is rotating
clockwise and just a few miles from me the island is moving a couple
millimeters per year.
Look for a \"GPS Control Points\" map on your county GIS web page or map
source. Here\'s mine from 1994:
<https://gis.santacruzcounty.us/DPWScans/recordmaps/087M48.pdf>
The notes under \"Basis of Bearing\" explains how the map works.
However, I barely understand the terminology and need to ask for help
before I can probably decode it. Anyway, you should have something
similar available. If you can find two or more such markers, you
should be able to orient your position plot to the map and adjust the
GPS locations.

Just to make things difficult, the above GPS Control Points map used
NAD83, while the GPS standard is WGS84. Fortunately, these are within
1 meter of each other in most of the USA, so I can ignore it for now
and use an online converter later:
<https://geodesy.noaa.gov/cgi-bin/HTDP/htdp.prl?f1=4&f2=1>


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
K

KenW

Guest
Property is expensive, that would be considered grand theft.


KenW
 
J

Jeff Liebermann

Guest
On Mon, 10 Aug 2020 14:22:26 -0600, KenW <ken1943@invalid.net> wrote:

Property is expensive, that would be considered grand theft.
KenW
Talk to your insurance agent to see if you\'re covered if your property
(land, not personal property) \"moves\" or \"disappears\". That\'s a very
real problem in the hills and mountains. When I asked, my house is
covered if it disappears, but the property is not covered. Notice
that even earthquake insurance does not cover disappearing property:
<http://www.insurance.ca.gov/01-consumers/105-type/95-guides/03-res/eq-ins.cfm>
Earthquake insurance covers some of the losses and damage
that earthquakes can cause to your home, belongings, and
other buildings on your property.

Incidentally, if I use the lat/long from the original 1926 survey, my
property overlaps a major part of my neighbors property across the
road including the house. Of course, the back side of my house would
be owned by the neighbors behind me. I mentioned this to the
neighbors when was initially doing my surveying but forgot to mention
that I was joking. The neighbors wife almost fainted.

Living on a hillside also has its entertainment value. It seems that
the road has moved about a few feet horizontally in Google Maps. The
problem is that every winter, the hillside slips an inch or two down
the hill, taking the road with it. A landslide into the road on the
uphill side of the road, and a landslide causing the edge of the road
to crumble on the downhill side of the road. We dig out the dirt from
the uphill side, and dump it on the downhill side. From above, it
looks like the road is moving.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
R

Ralph Mowery

Guest
In article <aae3jfti4blr3223qfmlj3rfa14jkc1cp9@4ax.com>,
jeffl@cruzio.com says...
Living on a hillside also has its entertainment value. It seems that
the road has moved about a few feet horizontally in Google Maps. The
problem is that every winter, the hillside slips an inch or two down
the hill, taking the road with it. A landslide into the road on the
uphill side of the road, and a landslide causing the edge of the road
to crumble on the downhill side of the road. We dig out the dirt from
the uphill side, and dump it on the downhill side. From above, it
looks like the road is moving.
I do not recall all the details from talking to a friend that has his
surveyers license. From what I geather it used to be you drug a chain
across the ground to get the footage. Now is is a streight shot. Being
that if you have land on a very steep hill at one time you might have
100 feet of property,but now it may only be listed as 75 feet, even if
nothing is changed.
 
J

Jeff Liebermann

Guest
On Mon, 10 Aug 2020 17:59:58 -0400, Ralph Mowery
<rmowery28146@earthlink.net> wrote:

In article <aae3jfti4blr3223qfmlj3rfa14jkc1cp9@4ax.com>,
jeffl@cruzio.com says...

Living on a hillside also has its entertainment value. It seems that
the road has moved about a few feet horizontally in Google Maps. The
problem is that every winter, the hillside slips an inch or two down
the hill, taking the road with it. A landslide into the road on the
uphill side of the road, and a landslide causing the edge of the road
to crumble on the downhill side of the road. We dig out the dirt from
the uphill side, and dump it on the downhill side. From above, it
looks like the road is moving.

I do not recall all the details from talking to a friend that has his
surveyers license. From what I geather it used to be you drug a chain
across the ground to get the footage. Now is is a streight shot. Being
that if you have land on a very steep hill at one time you might have
100 feet of property,but now it may only be listed as 75 feet, even if
nothing is changed.
Looking at the 1926 county map at:
<https://gis.santacruzcounty.us/DPWScans/recordmaps/024M02.pdf>
I\'m in section 18 on lots 20 and 21. Combined, these are listed on
the map as approximately 50 x 87 ft or 4350 sq-ft. The 87 ft part is
on the slope.

Looking at the current data from the county GIS site, the parcel size
for tax purposes shows 4225 sq-ft. Since the house is on an
approximately 45 degree slope, the 87 ft boundary line would need to
be about 123 ft if measured with a chain along the ground. Therefore,
it seems that the local boundaries are measured horizontally since at
least 1926. I have no clue why my property shrank 125 square feet in
the last 94 years. Probably termites.



--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
J

Jon Elson

Guest
etpm@whidbey.com wrote:


Thanks for all the great info Jeff. This surveying I want to do is
not for legal reasons, mainly to just make sure I know where some of
the property line probably is and where a corner marker should be.
Go to the county recorder of deeds office and ask to see your plat book.
It will be greek to most people, but should have a definition of the
property boundary relative to other properties. With a little work, you may
be able to figure out how it abuts other lots.

If you have a sensitive compass, you can slowly sweep it over the suspected
corners and see if you can get the needle to spin. The surveyors drove iron
pipes with magnets in them at the corners of the lot. If you have a metal
detector, that can be used to home in on likely objects, then check them for
magnets with the compass.

Jon
 
J

Jon Elson

Guest
Jeff Liebermann wrote:


In this area, as soon as the surveyors are done, the locals like to
move the markers to a location that favors their property. Two of my
neighbors were having a dispute over a lot line adjustment. They paid
a professional surveyor to survey the property. I was home at the
time and watched them work. I then photographed the location of all
the markers because two of them were one side of my property. Two
days later, the markers had all moved. I\'ll spare you the rest of the
fiasco. At one point, I used a smartphone and Mobile Topographer Free
to demonstrate that the markers had been moved, which mostly solved
the problem.
In most states, tampering with a survey marker is a felony. Not the little
sticks with the dayglo tape on them, but the buried iron pipes with magnets.
If you called the surveyors, they\'d at least know who to call to report it.
They would not be happy, as moving these markers complicates their work the
next time they come out to survey.

Jon
 
S

server

Guest
On Mon, 10 Aug 2020 19:36:39 -0500, Jon Elson <elson@pico-systems.com>
wrote:

etpm@whidbey.com wrote:


Thanks for all the great info Jeff. This surveying I want to do is
not for legal reasons, mainly to just make sure I know where some of
the property line probably is and where a corner marker should be.
Go to the county recorder of deeds office and ask to see your plat book.
It will be greek to most people, but should have a definition of the
property boundary relative to other properties. With a little work, you may
be able to figure out how it abuts other lots.

If you have a sensitive compass, you can slowly sweep it over the suspected
corners and see if you can get the needle to spin. The surveyors drove iron
pipes with magnets in them at the corners of the lot. If you have a metal
detector, that can be used to home in on likely objects, then check them for
magnets with the compass.

Jon
I have the county maps and have seen the one corner marker I\'m looking
for but I think it is now under about 6 feet of tipped over hemlock
tree root ball. If there is an iron pipe as you suggest it is also
under that root ball. How often do surveyors drive this pipe? Is it a
law? I like that magnet idea. I wonder how hard it will be to detect
if it is under 6 feet of dirt and roots?
Eric
 
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