GPS - consumer grade GPS for surveying?

Author

consumer grade GPS for surveying?

David Koski

2008-02-10, 4:33 am

I have found (via google) that consumer grade GPS units made today have
an accuracy of about 3 meters. I would like to find the corner points to
my property and can identify some survey markers that I could use as a
reference. Is it possible to calibrate a consumer grade GPS to a known
reference to improve the accuracy and if so, by how much?

Regards,
David Koski
david@kosmosisland.com

Mark F

2008-02-10, 10:33 am

In a word, no. Not without DGPS (Differential) and some fancy
phase detection stuff inside the unit. However, there is nothing
to stop you from averaging readings over a longer period of time,
which will perhaps get within a few meters, assuming you have
enough battery power to get you thru it... /mark

David Koski wrote:
> I have found (via google) that consumer grade GPS units made today have
> an accuracy of about 3 meters. I would like to find the corner points to
> my property and can identify some survey markers that I could use as a
> reference. Is it possible to calibrate a consumer grade GPS to a known
> reference to improve the accuracy and if so, by how much?
>
> Regards,
> David Koski
> david@kosmosisland.com

Ken Abrams

2008-02-10, 10:33 am

"David Koski" <david@kosmosisland.com> wrote

>I would like to find the corner points to
> my property and can identify some survey markers that I could use as a
> reference.

Depending on the number and placement of the known markers, a little
"simple" geometry might serve you better.

Pieter

2008-02-10, 10:33 am

If you are looking for an existing corner marker, about any GPS will get you
close, as you point out. However, for actually placing a corner marker, no
consumer grade GPS will be accurate enough. The use of WAAS is probably as
accurate as real time DGPS as provided by the old US Coast Guard (now I
believe DOT) real time correction broadcast system. I used DGPS for a few
years, then when WAAS became universal, I went with that. DGPS real time
corrections are better the closer you are to the ground station. I am only
about 20 miles from one, and even so, it was not any more accurate that
WAAS. In addition, DGPS coverage has some holes it in.

Some Garmin models (the old 12 xl for example), were capable of producing
satellite ephemeris data which is required for post-processing. In this
scheme, the position data of individual satellites is recorded and corrected
after-the-fact using data downloaded from the web. However, it really
doesn't improve enormously on the current WAAS correction system, and you
can't find a position "on the fly" since corrections aren't added in real
time.

In short, using a commercial grade GPS and survey ssystem (see Trimble.com)
is really necessary for defensible results.

In my part of the world, most of the bounds are done as compass bearings and
distances from a known stake or point, so using a good lensatic compass and
an accurate tape is probably easier than trying it with a GPS around here.

"Mark F" <markotime@shaw.ca> wrote in message
news:2YDrj.12182$FA.8099@pd7urf2no...[color=darkred]
> In a word, no. Not without DGPS (Differential) and some fancy
> phase detection stuff inside the unit. However, there is nothing
> to stop you from averaging readings over a longer period of time,
> which will perhaps get within a few meters, assuming you have
> enough battery power to get you thru it... /mark
>
> David Koski wrote:

Pegleg

2008-02-10, 10:33 am

On 10 Feb 2008 06:28:24 GMT, David Koski <david@kosmosisland.com> wrote:

>I have found (via google) that consumer grade GPS units made today have
>an accuracy of about 3 meters. I would like to find the corner points to
>my property and can identify some survey markers that I could use as a
>reference. Is it possible to calibrate a consumer grade GPS to a known
>reference to improve the accuracy and if so, by how much?
>
>Regards,
>David Koski
>david@kosmosisland.com

No!

Stichting ST

2008-02-11, 4:33 am

I can confirm the remark that with a old Garmin GPS12 you can get better
results doing postprocessing.
But it is, in the case mentioned, not really praticable.
You have to observe at a fixed point voor an hour and then use data from a
nearby reference station.
And with some luck you have a position within 40 cm accurate (95 %
confidence).
If you are intereseted I tell about it here:

http://www.xs4all.nl/~atarist/geo/gps_accuracy.htm

On Sun, 10 Feb 2008 09:50:33 -0500, "Pieter" <pvcl@*nospam*plitch.com> wrote:

>If you are looking for an existing corner marker, about any GPS will get you
>close, as you point out. However, for actually placing a corner marker, no
>consumer grade GPS will be accurate enough. The use of WAAS is probably as
>accurate as real time DGPS as provided by the old US Coast Guard (now I
>believe DOT) real time correction broadcast system. I used DGPS for a few
>years, then when WAAS became universal, I went with that. DGPS real time
>corrections are better the closer you are to the ground station. I am only
>about 20 miles from one, and even so, it was not any more accurate that
>WAAS. In addition, DGPS coverage has some holes it in.
>
>Some Garmin models (the old 12 xl for example), were capable of producing
>satellite ephemeris data which is required for post-processing. In this
>scheme, the position data of individual satellites is recorded and corrected
>after-the-fact using data downloaded from the web. However, it really
>doesn't improve enormously on the current WAAS correction system, and you
>can't find a position "on the fly" since corrections aren't added in real
>time.
>
>In short, using a commercial grade GPS and survey ssystem (see Trimble.com)
>is really necessary for defensible results.
>
>In my part of the world, most of the bounds are done as compass bearings and
>distances from a known stake or point, so using a good lensatic compass and
>an accurate tape is probably easier than trying it with a GPS around here.
>
>
>
>"Mark F" <markotime@shaw.ca> wrote in message
>news:2YDrj.12182$FA.8099@pd7urf2no...
>

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