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<title>[Proj] RE: geoid in Kalimantan, Indonesia</title>
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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Frans,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Again I agree with Clifford. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>It sounds like you’ve been working your tail off in a hot,
humid, muddy environment. I don’t know what economics you’re
working with or if the opportunity has passed with but wouldn’t it be
easier to rent a set of dual frequency receivers and perform your survey? <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Given the circumstances it seems that you’ve been incorrectly
advised as to how this project could have been performed. <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Of course the Promarks may have been the GPS’s you had at
the time, but in the scheme of things it’s a “right tools for the
job” approach as I assume the cost of getting your team on site is the
greater cost.<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
proj-bounces@lists.maptools.org [mailto:proj-bounces@lists.maptools.org] <b>On
Behalf Of </b>Clifford J Mugnier<br>
<b>Sent:</b> Saturday, 8 March 2008 3:24 AM<br>
<b>To:</b> PROJ.4 and general Projections Discussions<br>
<b>Subject:</b> RE: [Proj] RE: geoid in Kalimantan, Indonesia<o:p></o:p></span></p>
</div>
</div>
<p class=MsoNormal><o:p> </o:p></p>
<div id=idOWAReplyText53535>
<div>
<p class=MsoNormal><span style='font-size:10.0pt;color:black'>How much
improvement on accuracy? This is not quantifiable by rule of thumb.
Long practice in one locale with the ability to compare with classical
control versus geoid quality, geoid fit, and geoid slope will yield estimators
that come with experience. For concrete comparisons and properly scaled
error propagation analyses, we use dual-frequency receivers and we then are
able to determine various improvements in accuracy with changes in the
variables.</span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>In the boondocks with
single-frequency receivers and LONG baselines, you don't really have sufficient
information to know what you don't know. An estimator is the number of
epochs observed and the ratio of fixed to float solutions. Keep your
fingers crossed.</span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal> <o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Sorry.</span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'> </span><o:p></o:p></p>
</div>
<div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Clifford J. Mugnier, C.P.,
C.M.S.</span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>LSU Student ASCE Chapter
Faculty Advisor</span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>and<br>
National Director (2006-2008),<br>
Photogrammetric Applications Division<br>
American Society for Photogrammetry and Remote Sensing </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>and </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Chief of Geodesy,<br>
CENTER FOR GEOINFORMATICS </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Department of Civil
Engineering </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>CEBA 3223A<br>
LOUISIANA STATE UNIVERSITY </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Baton Rouge, LA 70803<br>
Voice and Facsimile: (225) 578-8536 [Academic] </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Voice and Facsimile:
(225) 578-4474 [Research] </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Honorary Life Member of the </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Louisiana Society of
Professional Surveyors </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Member Emeritus of the ASPRS </span><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><span style='font-size:10.0pt'>Member of the Americas
Petroleum Survey Group<br>
======================================================<br>
<a
href="https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.ls"
target="_blank">http://www.asprs.org/resources/GRIDS/</a><br>
======================================================</span><o:p></o:p></p>
</div>
</div>
</div>
<div>
<p class=MsoNormal><o:p> </o:p></p>
<div class=MsoNormal align=center style='text-align:center'>
<hr size=3 width="100%" align=center>
</div>
<p class=MsoNormal style='margin-bottom:12.0pt'><b><span style='font-size:10.0pt;
font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;
font-family:"Tahoma","sans-serif"'> proj-bounces@lists.maptools.org on behalf
of Frans Buschman<br>
<b>Sent:</b> Fri 07-Mar-08 03:00<br>
<b>To:</b> proj@lists.maptools.org<br>
<b>Subject:</b> [Proj] RE: geoid in Kalimantan, Indonesia</span><o:p></o:p></p>
</div>
<div>
<p><span style='font-size:10.0pt'>Hello again,<br>
<br>
Thanks for your useful replies, Clifford and Andrew. The best geoid<br>
available is thus the EGM96 and I understand that this accuracy is at<br>
best 1 m vertically worldwide.<br>
Indeed we did not have the luxury of having control sites and indeed it<br>
was difficult to decrease the spacing due to dense vegetation or<br>
mangrove swamps. We have just used two GPS promark 3 receivers<br>
simultaneously at locations maximally 30 km apart to measure the<br>
relative height differences. You mention that the vertical accuracy of<br>
this system over these distances is 1or 2 m at best. So, combining these<br>
errors it seems more reliable to average the tidal gauges and assume<br>
that they have the same mean level!<br>
<br>
One question, out of curiosity, remains: we realised that the distances<br>
between the stations were long for this GPS promark 3 system, so we<br>
performed the measurements during the night since we assumed that the<br>
least ionospheric error would be made then. How much does this improve<br>
the accuracy?<br>
<br>
Thanks again,<br>
Frans<br>
<br>
<br>
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> 1. RE: geoid in Kalimantan, Indonesia (Andrew Williams)<br>
><br>
><br>
> ----------------------------------------------------------------------<br>
><br>
> Message: 1<br>
> Date: Thu, 6 Mar 2008 17:44:14 +1100<br>
> From: Andrew Williams <AWilliams@rapidmap.com><br>
> Subject: RE: [Proj] geoid in Kalimantan, Indonesia<br>
> To: "PROJ.4 and general Projections Discussions"<br>
> <proj@lists.maptools.org><br>
> Message-ID:<br>
>
<29C3A52E0876C94C97BD6443FA96F7332E9EE291F9@rms03.rapidmap.local><br>
> Content-Type: text/plain; charset="us-ascii"<br>
><br>
> Frans,<br>
> I tend to agree with Clifford. As a surveyor myself and having used the
ProMark3's in anger I can say the manufacturers specifications leave the whole
"accuracy depending on atmosphere" open to interpretation. When I
read your post I assumed you'd performed a static differential survey with a
pair of ProMarks to build a network including your tide gauges. If you have
simply positioned your Promark above the tide gauge and observed for 20 or 30
minutes then your results are likely to be poor.<br>
><br>
> I have always used a rule of thumb that the vertical accuracy of a GPS is
about 2.5-3 time worse than the quoted horizontal accuracy in RELATIVE terms.
What you're trying to do is perform a gravity survey in ABSOLUTE terms. I've
done countless surveys for irrigation over vast tracts of land. They key here
is you need an accurate vertical geoidal model upon which to base your survey.
Typically I've had the benefit of connecting to existing bench marks that were
leveled with spirit or optical leveling techniques. Since both the spirit or
optical levels are affected by gravity you have a great framework for basing
your GPS survey.<br>
><br>
> Most of my work has been using Thales/Magellan DSNP Dual Frequency Long
Range Kinematic GPS. They way we use this is to set up a base station in a
convenient location.(Usually a high hill/mountain) within 40km of the job.
There will be surveyors reading this saying I'm crazy, but believe me Thales
mean LONG range kinematic.<br>
> Anyway I'd observe a network of previously established bench marks with
Horizontal and vertical coordinates. That would establish my survey reference
framework. After that any new or unknown points would then be coordinated
relative to this framework.<br>
> In your case you may not have this network of existing
"control". This is the challenge. I have transferred control using
the above technique. What that means is as you survey points that are unknown
as above they become "known". You can then pick up your equipment,
transfer it to a convenient location closer to job site and use then new
benchmarks as control for the new site.<br>
> This is not a job to be taken lightly. I'm also not too sure what the
terrain is like in Kalimantan but I assume difficult to traverse.<br>
><br>
> From: proj-bounces@lists.maptools.org [<a
href="mailto:proj-bounces@lists.maptools.org">mailto:proj-bounces@lists.maptools.org</a>]
On Behalf Of Clifford J Mugnier<br>
> Sent: Thursday, 6 March 2008 2:50 AM<br>
> To: PROJ.4 and general Projections Discussions<br>
> Subject: RE: [Proj] geoid in Kalimantan, Indonesia<br>
><br>
> EGM96 is the best worldwide geoid available, but a Promark is a
single-frequency receiver and is a poor candidate for the third
component. I would estimate the vertical accuracy at about plus or minus
1 to 2 meters at best. A dual frequency receiver can get fairly reliable
verticals because the two frequencies allow proper modeling of tropospheric
effects - an impossibility with only a single frequency receiver. A short
baseline differential technique (less than one kilometer with two simultaneous
Promarks) is used for construction work, but certainly not even close to 10
kilometers muchless 30!<br>
><br>
> Clifford J. Mugnier, C.P., C.M.S.<br>
> LSU Student ASCE Chapter Faculty Advisor<br>
> and<br>
> National Director (2006-2008),<br>
> Photogrammetric Applications Division<br>
> American Society for Photogrammetry and Remote Sensing<br>
> and<br>
> Chief of Geodesy,<br>
> CENTER FOR GEOINFORMATICS<br>
> Department of Civil Engineering<br>
> CEBA 3223A<br>
> LOUISIANA STATE UNIVERSITY<br>
> Baton Rouge, LA 70803<br>
> Voice and Facsimile: (225) 578-8536 [Academic]<br>
> Voice and Facsimile: (225) 578-4474 [Research]<br>
> Honorary Life Member of the<br>
> Louisiana Society of Professional Surveyors<br>
> Member Emeritus of the ASPRS<br>
> Member of the Americas Petroleum Survey Group<br>
> ======================================================<br>
> <a href="http://www.asprs.org/resources/GRIDS/">http://www.asprs.org/resources/GRIDS/</a><https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=https://email.lsu.edu/exchweb/bin/redir.asp?URL=<a
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ir!<br>
> .asp?URL=<a
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> ======================================================<br>
><br>
> ________________________________<br>
> From: proj-bounces@lists.maptools.org on behalf of Frans Buschman<br>
> Sent: Wed 05-Mar-08 05:03<br>
> To: proj@lists.maptools.org<br>
> Subject: [Proj] geoid in Kalimantan, Indonesia<br>
><br>
> Hello,<br>
><br>
> In a coastal region in East Kalimantan, Indonesia, we measured with a GPS
promark3 system height differences of several water level gauges with respect
to the WGS-84 ellipsoide and datum. The stations are about 30 km apart and we
think that the precision of the measurements is within 10 cm.<br>
><br>
> >From the water level gauges we want to see in what direction water
should be flowing, so we want the want to derive the height differences with
respect to a geoid. For Kalimantan no detailed geoid seems to exist, so I would
like to convert measured height differences on the WGS-84 ellipsoide to height
differences on a global geoid. Which geoid is best for this purpose and how can
I make the conversion? Could you give an estimate of the error you make with
this conversion?<br>
><br>
> Thanks!<br>
> Frans<br>
><br>
> --<br>
> ______________________________________________________<br>
> Frans Buschman (PhD student)<br>
> Department of Physical Geography<br>
> Institute for Marine and Atmospheric Research Utrecht<br>
> Utrecht University<br>
> P.O. box 80.115 / Heidelberglaan 2<br>
> 3508 TC Utrecht, the Netherlands<br>
> Room 211 in Jan Zonneveldvleugel<br>
> Phone: +31 - (0)30 2532778<br>
> Fax: +31 - (0)30 2531145<br>
> mail: f.buschman@geo.uu.nl<br>
> ______________________________________________________<br>
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<br>
--<br>
______________________________________________________<br>
Frans Buschman (PhD student)<br>
Department of Physical Geography<br>
Institute for Marine and Atmospheric Research Utrecht<br>
Utrecht University<br>
P.O. box 80.115 / Heidelberglaan 2<br>
3508 TC Utrecht, the Netherlands<br>
Room 211 in Jan Zonneveldvleugel<br>
Phone: +31 - (0)30 2532778<br>
Fax: +31 - (0)30 2531145<br>
mail: f.buschman@geo.uu.nl<br>
______________________________________________________<br>
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