Subject: G.I.S.
From: joedheav@aol.com (JOE D HEAV)
Date: 20 Jan 1997 18:34:54 GMT
Has anybody knowledge of a sucessful G.I.S. project using 1"=200' Digital
Ortho Photo Mapping? It seem to me that at that scale, much detail is
lost, and any advantages of digitizing manholes, valves, catch basins,
etc. is not possible because of the resolution. It also seems to me that
at 1"=200' locational error of any particular point would be in the range
of 5' more or less.
Subject: Re: GPS (?) LAT/LONG +/- 25'
From: cothrun@ix.netcom.com (Chris Cothrun)
Date: Mon, 20 Jan 1997 21:47:25 GMT
harmon@nextex.net (Harlan Scott Harmon P.S.) wrote:
>I am a surveyor in Columbus Ohio. I have my own consulting buisiness,
>and also am the chief Surveyor for a corporation that is in the
>cellular buisiness. We run 3 crews and I am looking to buy a GPS
>system to locate LAT/LONG for FAA data needed for applications for
>cellular tower sites, also to obtain a true azimuth (and quite wasting
>time with hasty solar observations). The system I am looking at is the
>Topcon turbo g-2 hand held reciver using an external antenna,, and 2
>units I would like to get +/- 25'. Topcon has told me that using a
>Coast Gaurd becon (if available) I would get better results, and the
>post-process program I can achieve my goal.
You should get the best results with a post-processing program, but
the Coast Guard beacon should put you at or under your +/- 25'. The
Coast Guard beacon will give you real time results, post processing
will not. If I understand your application correctly, you shouldn't
need real time corrections (although they are nice and you might find
other applications for them).
> The cost I belive will be
>around $11,000 with 2 recievers, external attenas, radio reciever, 2
>tripods, postprocess software, and a new laptop. Does anyone know of
>a similar system that I can get for the same $$Money or less,and that
>will get the results.
That seems about right if you are going for a real-time link. If you
just want post-processed data you could save some of the money.
> Or is any of this info seem un-realistic, I
>have been told by another, that is very active in geodetic GPS work
>that I can not overcome the 300'(government Scramble) unless I occupy
>a know USGS or GPS coordinate,
To get absolute Lat / Lon on a point you will have to occupy a point
with known coordinates with one of the receivers. If you have access
to the Coast Guard beacon you should be able to use that since those
corrections should be based on known coordinates.
> although Topcon says that they stand
>behind there promise.
There are a couple of things you can do to make it easier to occupy a
known point. You can set your own point at your office or other
convenient location from a known point. Obtain several sessions of
data and process each one to get an idea of the repeatability of your
coordinates.
You can also average GPS data to get a better idea of your
coordinates. You need nearly a day's worth to get within several
meters accuracy.
>this week I an going on a test with a salesman,
>we will compare the info from the GPS to a known baseline.
Make sure that whatever he shows you matches the situations you will
actually be using the receivers with.
I've sold two systems (similar to TOPCON's, but from Magellan) for
nearly the same application. One to a surveyor, the other to Centel
Cellular. The surveyor uses his post-processed, Centel purchased a
beacon receiver to have the ability to do real time or post-processed.
Both tell me they are happy with the capabilities of the systems.
Disclaimer: I'm not a surveyor, I'm a sales / repair guy. I sell
TOPCON and would be happy to see them sell you a system. I don't have
access to a Coast Guard beacon in my area because I live in the desert
and the Coast Guard hasn't seen fit to supply us with GPS corrections.
Take my advice with a grain of salt.
Chris Cothrun
cothrun@ix.netcom.com
Subject: Re: Board of Registration standards for GPS surveys
From: "David and Lorri Ferguson"
Date: Mon, 20 Jan 1997 17:29:33 -0800
Phil wrote in article <5bqmj0$kc$1@news.ime.net>...
> Does anyone know of any State, Province, or other ruling body that has
> formulated published standards of pratice for performing GPS surveys etc.
> ?
> I am interested in obtaining opinions as to whether GPS double fixes on
> points meets the requirement of having a closed traverse as is required
> for all boundary surveys using conventional surveying methods.
>
> Thanks
>
> Phil
>
>
South Carolina State Board of Registration
for Professional Engineers and Land Surveyors
Policy Statement - Geodetic/Global Positioning Systems (GPS) Surveys
(Based on R. 49-430C18)
1. All geodetic surveys, both vertical and horizontal, in the State of
South Carolina shall be under the direction of a land surveyor registered
in the State of South Carolina.
2. Terrestrial geodetic surveys represented to a client os meeting first,
second or third order standards shall conform to the Standards and
Specifications for Geodetic Control Networks as set forth by the Federal
Geodetic Control Committee (FGCC) or its successor in their most current
publication.
3. Global Positioning Systems (GPS) geodetic surveys represented to a
client as meeting first, second or third order standards shall conform to
the Geometric Geodetic Accuracy Standards and Specifications for Using GPS
relative positioning Techniques as set forth by the Federal Geodetic
Control Committee (FGCC) or its successor in their most current
publication.
4. GPS surveys not required to be performed to the above standards and not
otherwise specified in this document shall be designed by the surveyor to
meet the needs of the client and certified by the surveyor in responsible
charge, as to the methods, procedures, positional uncertainties, datum,
specific control points held and other such relevant data so as to qualify
the work performed.
5. Land property corners positioned by GPS where specifications in item 3
are not required may be surveyed by a variety of GPS techniques with the
surveyor excersizing judgement as to the most appropriate within the
following constraints:
a. Property corners shall be positioned from the nearest first or second
order horizontal control points int the state geodetic data base. To
maintain compatibility with the local geodetic network it is not good
practice to extend control over existing monuments to a project area.
b. All property corners shall be positioned from at least 2 geodetic
control monuments contained in the state geodetic database. Property
corners shall be positioned to a horizontal accuracy of at least 1/20,000
or 0.2 feet (whichever is smaller) with relation to the nearest first or
second order geodetic control monument.
c. Survey grade GPS receivers (stated accuracy better than 5cm + 2ppm)
shall be used for positioning property corners to be shown on a survey plat
or used in a legal description. Mapping grade receivers (stated accuracy
in excess of 5cm + 2ppm) may be used in unusually inaccessible areas for
positioning boundary lines defined by a water body (i.e. center of stream
or highwater mark), ridge lines or other boundary lines impractical to
survey by conventional methods. The intent in allowing mapping grade use
is to obtain better boundary line delineation and more accurate acreage
determination htan could normally be obtained under exceptionally difficult
field conditions.
6. For the purposes of the South Carolina State Plane Coordinate System,
the foot is the the International Foot with one inch being exactly 2.54
centimeters. To convert metric coordinates to international feet multiply
by 3.280839895.
7. Horizontal coordinates shall be referenced to North American Datum of
1983 (NAD 83). Vertical control may be referenced to National Geodetic
Vertical Datum of 1929 (NGVD 29) or North American Vertical Datum of 1988
(NAVD 88), according to client requirements. The datum used as a reference
shall be clearly shown, and the horizontal and vertical control stations
used to originate a survey shall be clearly noted along with their
published coordinates and/or elevation.
8. Certified drawings prepared to document GPS surveys shall contain
methods, procedures, position uncertainties, datum, specific control points
held and other such relevant data so as to qualify the work performed. A
note shall explain why any published control values were allowed to take
adjustment. When establishing elevations by GPS methods, the geoid model
used shall be stated and the bench marks used to establish elevations shall
be noted.
Hope this will be of some help to you.
David Ferguson, SCPLS
Subject: Re: GPS (?) LAT/LONG +/- 25'
From: FRAN WEST
Date: Tue, 21 Jan 1997 12:41:28 +0000
Can I ask how long is your baseline, and how quickly you want to
establish it in observation terms. Also how much error can you tolerate
on the baseline azimuth?
In article <5bs9l2$r3e@news2.ee.net>, "Harlan Scott Harmon P.S."
writes
>
>
>I am a surveyor in Columbus Ohio. I have my own consulting buisiness,
>and also am the chief Surveyor for a corporation that is in the
>cellular buisiness. We run 3 crews and I am looking to buy a GPS
>system to locate LAT/LONG for FAA data needed for applications for
>cellular tower sites, also to obtain a true azimuth (and quite wasting
>time with hasty solar observations). The system I am looking at is the
>Topcon turbo g-2 hand held reciver using an external antenna,, and 2
>units I would like to get +/- 25', Topcon has told me that using a
>Coast Gaurd becon (if available) I would get better results, and the
>post-process program I can achieve my goal. The cost I belive will be
>around $11,000 with 2 recievers, external attenas, radio reciever, 2
>tripods, postprocess software, and a new laptop. Does anyone know of
>a similar system that I can get for the same $$Money or less,and that
>will get the results. Or is any of this info seem un-realistic, I
>have been told by another, that is very active in geodetic GPS work
>that I can not overcome the 300'(government Scramble) unless I occupy
>a know USGS or GPS coordinate, although Topcon says that they stand
>behind there promise. this week I an going on a test with a salesman,
>we will compare the info from the GPS to a known baseline.
>
>Any replys are welcome:
>
>thanks, Scott Harmon P.S. (harmon@nextek.com) or
>(ScottH@divinet.com)
>
Fran West
Veripos UK, 95 Shore Street, Fraserburgh,Aberdeenshire,Scotland.
Tel 44 1346 511411, Fax 44 1346 513112
Providers of Precise navigation systems to Professional Users.
You get what you pay for, only monkeys work for peanuts.
Subject: Tired of pound stakes?
From: tcsurvey@aol.com (TCSURVEY)
Date: 21 Jan 1997 14:58:07 GMT
If you like surveying and would like to stay close to the industry, then
this may be of interest to you. Do you like high tech gear? If so, this
message may be of interest to you. Do you enjoy interacting with other
surveyors and people in general?
If you answered yes to the questions above you should think about applying
for a position with Topcon California as a sales representative. We
service the surveying, engineering and related industries. We sell sate
of the art equipment such GPS, total stations, digital levels and more.
The job is challanging and rewarding for the right kind of person.
Again, if your answer was yes to the above questions send your resume to:
Topcon California
3380 Industrial Blvd. Ste 105
West Sacramento, CA 95691
Fax# 916-374-8329
