Geodetic Solutions
Mike Potterfield, LS
MikePotterfield@geodeticsolutions.com
Voice:
(831) 659-5764
Fax:
(831) 659-5896
Geodetic SolutionsMikePotterfield@geodeticsolutions.com
Voice:
(831) 659-5764
Fax:
(831) 659-5896
Consulting and contracting in geodesy, network adjustment, GPS
baseline processing, geodetic datums and map projections, analytical models,
and custom software development
Both
experienced surveyors and inexperienced users of geodetic control
networks may find that some networks present special requirements that can't
easily be met using standard commercial software. Geodetic Solutions can
provide expert assistance in developing and analyzing geodetic networks for a
wide variety of special needs, and can provide custom solutions for complex
geodetic problems. Geodetic Solutions can also solve
problems experienced by research scientists
in projects such as continuous surface modeling and crustal motion.
In
addition to commercially available software, Geodetic Solutions has access to a
large arsenal of geodetic laboratory software tools developed over a period of
many years and not available in commercial packages.
There
is information in this web page about the products, services, tools, fees,
contact information, and background
of Geodetic
Solutions. A list of related links and Frequently Asked Questions
can be found at the bottom of this page.
To upload files to this site, go to the ftp site ftp://ftp.geodeticsolutions.com/pub/uploads. If you upload a file, send an email
describing the upload to MikePotterfield@geodeticsolutions.com. To download files, go to ftp://ftp.geodeticsolutions.com/pub/download.
Inexperienced users:
A
geodetic control network should be carefully designed, constructed, observed, adjusted,
analyzed and maintained in order for it to provide a full lifetime of useful
control for such purposes as GIS base maps, image registration, photogrammetry,
construction, deformation analysis, or cadastral surveying. Important considerations include the
definition of the datum and coordinate system for the network. By focusing upon the use to which the network
will be put, Geodetic
Solutions can help design, survey, implement, and maintain such
networks.
Experienced
surveyors:
Complex
and very precise geodetic networks may require expert analysis in order to
realize the full accuracy and precision of the surveying observations used to
create them. Geodetic Solutions can provide
custom solutions to problems raised by such networks, and can detect and
eliminate systematic errors in control networks that can’t be isolated by
standard commercial software.
Research scientists:
Any
overdetermined system presents opportunities for a unique simultaneous solution
of the analytical model, leveraging the most precise observations in the system
and propagating formal errors. Geodetic Solutions
can create, adjust, and analyze a wide variety of spatial and time-dependent
systems.
Geodetic
Solutions Products:
·
Written
reports including numerical results, statistical analysis, spreadsheets,
graphical representations of data and statistics, and narrative. Geodetic Solutions can tailor custom reports to
meet the needs of clients.
·
Various
computer data files containing numerical results.
·
Maps
in computer raster format.
·
Custom
software.
·
Self-contained
surface models, including the geoid and the sea floor, including propagated
formal errors.
·
Off-site
and on-site consulting.
Geodetic
Solutions Services:
·
Network
design and preanalysis.
·
Network
adjustment including terrestrial, GPS and gravity observations, variance
component estimation, and detection and elimination of systematic errors with
parameter groups. Various types of
observations, such as static and RTK GPS vectors, or dual-frequency and
single-frequency GPS vectors, can be combined into a 
single network with the
observations being subclassed for separate estimation of random errors and
removal of biased errors. The default analytical
model for network adjustment is multi-height, providing the most accurate
determination of orthometric heights from GPS observations. This adjustment model rigorously processes
correlated terrestrial and multibaseline GPS observations, and also provides
for the creation of new, and improvement of existing, continuous surfaces such
as the geoid. Terrestrial observations
are carefully reduced to the mathematical model by computing and removing
refraction errors and skew normal corrections.
·
GPS
baseline processing.
·
Unique
solutions for dynamic networks observed over extended periods of time.
·
Adjustable
station velocities.
·
Custom
datums and conversions.
·
Custom
mapping projections.
·
Design
and implementation of GIS control networks.
·
Creation of terrain
models.
·
Creation
of continuous surface models such as sea level, the geoid, and oceanic
thermoclines, using least-squares collocation and least-squares prediction
·
Transformations
of coordinates: 1 to 9-parameter transformations.
·
Network
validation. Geodetic Solutions will review and
validate previously adjusted networks to help determine whether or not the
previous adjustments provide optimal results.
·
Network
diagnostics. Geodetic Solutions will review and
debug existing network adjustments that are not providing results of the
desired quality.
·
Legacy
networks. Geodetic Solutions will use
archived historical surveying observations originating years past to create a
current adjusted network on a modern datum.
·
Modeling
of station errors for individual stations.
·
Adjustment
of multibaseline GPS solutions, including GAMIT and TRIMMBP.
·
Crustal
deformation studies.
·
Deformation
analysis: subsidence, episodic movement, crustal motion, structural
movement. Geodetic Solutions can estimate the
vectors of apparent movement compared against the noise levels of the adjusted
observations to estimate the probability that apparent movement of monitored
points is statistically significant.
·
Weighted
coordinates, including sequential adjustments of fully formed covariance
matrices provided for existing networks.
·
Computation
of the proposed FGCS circular error statistic, and its use in testing new
networks for inclusion in the national spatial database.
·
Prediction
of future coordinates for any epoch for dynamic networks.
·
Computation
of 1-D, 2-D, 3-D, and 4-D confidence regions, at any level of significance,
with graphics.
·
Recommendations
and procedures for network maintenance. 
·
Recommendations
and procedures for network enhancements.
·
Use
of CORS, HARN, and other Reference Stations.
·
Planning
and execution of survey campaigns. Geodetic Solutions
will make field visits to the offices and project sites of clients for purposes
of planning and inspection of constructed networks, and will undertake to
organize and direct survey campaigns for the purpose of producing high-accuracy
control networks. Geodetic Solutions can summon the
resources necessary to bring precise geodetic coordinates to remote
geographical locations. If desired, Geodetic Solutions
can subcontract capable third-party survey companies to construct
new networks, will process the network, and will advise third-party survey
companies in the maintenance and enhancement of survey networks using
commercially available software.
·
Blue-booking of GPS
solutions
·
Custom
software to process ASCII output from commercial network adjustment
applications, including reconstruction of the network covariance matrix.
·
Leadership
and training in complex survey campaigns, data processing, and network
adjustment.
·
Inclusion
of gravity observations in combined networks.
·
Correlated
terrestrial observations.
·
The
most accurate determination of orthometric heights from GPS.
·
“Adjustment”
of record maps. Platted subdivisions can
be adjusted to fit found survey monuments so that searches can be undertaken
for corners not yet found. Each such
corner will have an error ellipse specifying the size of the search area.
·
Expert
processing of terrestrial observations of all types. Geodetic Solutions will reduce and insert
terrestrial observations from field notes into binary data for network
adjustment.
Geodetic
Solutions Tools:
·
Geodetic
Solutions
uses commercially released software from Trimble Navigation, including WAVE, TRIMNET
Plus, GPSurvey, and TGO for data processing.
·
In
addition, Geodetic
Solutions has a large arsenal of enhanced and non-commercial
software tools, most of which were developed in-house, that can be applied to
unusual and complex problems. Non-commercial
projects may qualify for baseline processing using research-oriented
multibaseline processors such as MIT’s GAMIT.
·
Experience in surveying
extending over nearly 40 years.
Geodetic
Solutions Fees:
The
fees charged by Geodetic Solutions will depend upon the type of work being
performed. The fee schedule includes the
following types of fees:
·
On-site
consulting: charged at a daily rate,
plus expenses.
·
Off-site
consulting: hourly rates, with a discount given for projects requiring more
than 20 hours.
·
Custom
software development: negotiable. Geodetic Solutions will hold the copyright on any
developed software, with the client being granted a permanent and possibly
exclusive license for use.
·
Computer
time: hourly rates.
Geodetic
Solutions Clients:
·
National
Geodetic Survey
·
·
Scripps
Orbit and
·
·
Condor
Earth Technologies
·
Northwest
Hydraulic Consultants
·
·
McPheeters and
Associates
·
·
Larsen
Consulting Group
·
Government
of
Contacting Geodetic Solutions:
MikePotterfield@geodeticsolutions.com
About Geodetic Solutions:
In
August 2001 Mike
Potterfield left Trimble Navigation after working as a geodesist at
that company for 14 years, where he was the principal author of the network
adjustment application TRIMNET Plus. His
professional background is described below:
Geodetic Science
Familiarity with global and local datums Software Engineering
Surveying
Professional associations
Scientific papers
Employment background
Education
Related links:
If you’d like this page to
include an additional link to a geodetic web site, send the address, and a
brief description of the web site, to links@geodeticsolutions.com.
www.ngs.noaa.gov National Geodetic Survey
http://igscb.jpl.nasa.gov/siteindex.html IGS Site index
http://www.terrasurv.com
Terrasurv surveys, celestial observations, and Geodetic Bulletin Board
http://mywebpages.comcast.net/donaldmulcare/ Don Mulcare’s geodetic web page
http://www.geodeticsolutions.com/article.html Report of a surveying/snorkeling expedition
to the Northwest Hawaiian Islands February-March, 2001
FAQ (Frequently Asked Questions):
If you’d like to have a
question answered on this web page, send it to faq@geodeticsolutions.com. Please specify whether or not it would be
acceptable to include your name when the question is posted.
Q. If I understood the issue correctly, you designed Trimnet to transform
GPS vectors onto the local reference frame and then process them sort of as if
they were terrestrial observations. Is
this correct? If so, do you treat them
from the standpoint of trig-functions and an iterated adjustment? Are there advantages in doing it this way,
would you say, in terms of better answers?
Chuck Ghilani told me he thought this didn't make sense and that he
would much prefer adjusting it in Earth-centered cartesians, using a linear,
single-pass adjustment. However, I'm
reading between the lines in Alfred Leick's book (Chapter 7), and I think I'm
understanding him to say he prefers to adjust on the local plane, like you.
A.
TRIMNET models GPS vectors on the ellipsoid associated with the current datum. Instead of delta XYZ, you get azimuth,
distance and height. As a result, the
observation equations are non-linear, and so may require more than one
iteration, especially if the approximate coordinates are way off. However, you should keep in mind that even if
you're modeling vectors in the ECEF Cartesian model, you may still have to
perform more than one iteration.
The great advantage of doing it TRIMNET's way is that you can model
geoid heights and other heights directly in the adjustment model. In the default two-height mode, you get
adjusted orthometric heights and adjusted ellipsoid heights, and therefore
adjusted geoid heights, directly from the adjustment solution. You can also adapt this model to use least-squares
collocation to produce a continuous surface (e.g. the geoid) complete with
formal errors.
If all that I wanted to do was to adjust GPS vectors, and I was not
interested in terrestrial observations or orthometric heights, and I didn't
care about station errors (errors in H.I. and centering), then I would agree
that the ECEF Cartesian model would be the logical choice. However, if you are interested in
multi-height adjustments, and if you want to combine terrestrial, GPS and even 
gravity observations in the adjustment, then modeling
all the observations on the ellipsoid makes things very much easier. If you're trying to adjust geoid heights in a
network using the ECEF model, things get quite complicated right away. You either have to use the hybrid adjustment
model in which condition equations are combined with observation equations, or
else you have to model separate 3-D points for the orthometric height and the
ellipsoid height, and then add observed latitude and longitude with weights to
keep the two positions in the same horizontal location.
Modeling observations on the ellipsoid offers much more flexibility,
including the possibility of modeling several surfaces at once, such as
sea-level, or oceanic thermoclines.
Q:
If 6 receivers are collecting data simultaneously, 2 sitting on control points
& 4 "roving", how many trivial baselines (dependant vectors) per
session are being observed?
A: It’s not clear that there are ever any trivial baselines when single-baseline
processors are being used. The argument
against trivial baselines has its origin in the days of the multi-baseline
solutions (e.g. Trimble's TRIMMBP). With such solutions, the full covariance
matrix with terms between all of the baseline components guarantees the
uniqueness of both the geometric and stochastic solution of the baselines, so
that when they are added to the network adjustment there is no loss of
information. If you have any TRIMMBP solutions lying around, you can see this
in action when a multi-baseline solution is included in an 
adjustment, and it looks like one of the baselines in
the multi-baseline solution is a sideshot, but in fact you'll see residuals
computed for the "sideshot" components. These residuals are based on
the residuals for the geometrically over-determined baselines in the solution,
in conjunction with the correlations between all the baselines.
However, when you only have a single-baseline processor -- and that includes
most of the commercial processors these days -- then there is a loss of data
when the "trivial" baselines are excluded from the network
adjustment. In other words, the "sideshot" vector that got residuals
in the multi-baseline solution won't get residuals from a single-baseline
solution.
In my view the best way to make up for the loss of data is to include all of
the “trivial” vectors in the adjustment. It's true that this will inflate the
number of degrees of freedom in the network, but the chi-square value (sum of
the weighted squares of the residuals) will also increase. I have tested this
on some big networks, and I have found that the a posteriori errors are quite
close to what they would have been if a multi-baseline solution with no trivial
vectors had been used.