Low Distortion Projections - Iowa Geographic Information Council

Report
Low Distortion Projections,
with GIS’t a Little Bit of
Geometrical and Physical Geodesy
Roger R. Patocka, P.E.
Engineer, Emmet County, Iowa
April 4, 2013
One goal of this presentation is an attempt to affirm and clarify the utility and
value of statewide coverage by LDP’s.
Another goal is to assist non-Geodesists in their quest to better understand
geodetic coordinate systems and their use in GIS.
This presentation highlights the roots of surveying and geodetic measurement
techniques and the convergence of GIS, Geodetic and Engineering / Surveying
Data.
Establishing LDP’s is a step in promoting better coordination and use of spatial
databases among the disparate GIS user communities.
 An Iowa DOT LDS RFP Selection Committee, including representatives of the Society
of Land Surveyors of Iowa and the Iowa County Engineers Association, have evaluated
and recommended selection of a proposal for design and documentation of a Low
Distortion Projection coordinate system for the state of Iowa on March 13.
 A goal of 20 ppm maximum distortion for each LDP zone in Iowa has been set.
 Another goal is to keep the number of zones to a minimum while not crossing
county lines.
 An LDP Handbook/User Guide will be developed by the Consultant to assist the Iowa
Surveying, Engineering and Geospatial user community to implement use of Iowa’s
LDP Coordinate Reference System.
Some Advantages of LDP
1.
2.
3.
4.
5.
Projected (grid) distances very close to actual (ground) horizontal distances.
Less distortion over larger areas compared to project sites.
Reduced convergence angles (assuming central meridian centered in zone).
Can estimate distortion levels from field topographic elevation for most areas.
Simple zone parameter definitions compatible with surveying, engineering and
GIS software.
6. Ease of transformation between other coordinate systems.
7. Relationship maintained to NGS NSRS by allowing direct use of published NGS
control coordinates (latitude, longitude, ellipsoid height and elevation).
8. Coverage for entire cities and counties, facilitating regional mapping and GIS
applications.
9. More potential for statewide uniformity.
10. Standard projections may be inadequate:
• UTM distortion is 1 : 2,500 ( 400 ppm or 2.1 ft per mile).
• SPC distortion is 1 : 10,000 (100 ppm or 0.5 ft per mile).
• But in both above cases, distortion at ground is usually much greater.
• LDP goal of 20 ppm offers 1 : 50,000 or 0.1 ft per mile.
Errors, Distortions and Accuracy
Closure:
Traverse Adjustments:
Transit Rule, Compass Rule, Crandall Method
Least Squares Adjustment
Horizontal control accuracy standards for traverse
Errors, Distortions and Accuracy
Equipment Specifications:
PPM (Please Prevent Misunderstanding)
 Please don’t confuse 175 ppm traverse accuracy, or 10 mm + 1
ppm equipment specs, with a 20 ppm LDP design.
 A specification or description that includes a numerical value of
‘x’ ppm can have different meanings depending upon its
context.
 LDP does not change the responsibilities of Land Surveyors,
Engineers and/or GIS professionals to properly use their tools.
Plane Surveying Techniques
Plane Surveying Techniques
Plane Surveying Techniques
Plane Surveying Techniques
GIS’t a Little Bit of
Geometrical and Physical Geodesy
“I was taking a course in geographic
information systems (GIS) and during
an exercise, came upon a dialog box
with a field whose value indicated
the datum to which my data
referred. I had no idea what this
meant, so I asked another student. I
was told, ‘Who knows? Just accept
the defaults.’”
Meyer, Thomas H., Introduction to Geometrical and Physical Geodesy, ESRI Press, ISBN 978-1-58948-9, p. ix
The Need for Geodetic Surveying
Target h increases with distance c from the observation station.
Trading height for position…
Assuming a flat earth makes distant objects appear lower and farther away
than they really are.
Meyer, Thomas H., Introduction to Geometrical and Physical Geodesy, ESRI Press, ISBN 978-1-58948-9, pp. 55-56
Geodetic Coordinate Systems
Earth-Centered, Earth-Fixed Geocentric Cartesian (XYZ)
Meyer, Thomas H., Introduction to Geometrical and Physical Geodesy, ESRI Press, ISBN 978-1-58948-9, pp. 73-76
Geodetic Coordinate Systems
Local Horizontal Geodetic East-North-Up (ENU)
Meyer, Thomas H., Introduction to Geometrical and Physical Geodesy, ESRI Press, ISBN 978-1-58948-9, pp. 76, 81-84
Geodetic Coordinate Systems
Geodetic Longitude and Latitude, and Ellipsoid Height (LBH)
Meyer, Thomas H., Introduction to Geometrical and Physical Geodesy, ESRI Press, ISBN 978-1-58948-9, pp. 76-80
Transformations Between Frames:
ECEF Geocentric Cartesian (XYZ) and
Geodetic Lon-Lat, and Ellipsoid Height (LBH)
Ellipsoid, Geoid and Topography
Relationships
Deflection of the Vertical
Relationships between Ellipsoid Height (h),
Geoid-Ellipsoid Difference (N), and Elevation (H)
NGS Geoid-96
http://www.ngs.noaa.gov/GEOID/GEOID96/
The Zooming function can give a false sense of higher accuracy.
Assembling Technologies that Span Different
Time Periods, Skills and Disciplines
Plane Surveying
Self-Adjusting Level
Geodetic Surveying (Geodesy)
Traditional Maps
Global Position System
(GPS) Satellite
→
Transit
→
Mash-Up???
3D CADD
Survey-Grade GPS Base & Rover
Scanner
Total Station
Photogrammetry & Remote Sensing
Convergence of GIS and Engineering / Surveying Data
Projections
LDP’s help quantify linear distortion due to Earth
curvature and ground height above ellipsoid.
Using LDP’s to Help Budget Distortions
Making Decisions from Mash-ups of Data,
Disciplines and Personalities
“We need to think of technology as a
social enterprise, with interlocking
elements of hardware, software, and
squishyware, or, better, socialware.”
(Wenk, Edward, Jr., Making Waves, University of Illinois Press,
ISBN 0-252-02149-5, 1995, p. 11)
Making Decisions from Mash-ups of Data,
Disciplines and Personalities
“Given that survival of the species is the
transcendent goal, we may need a new survival kit in
collective learning and action.
In a free society, this requires consensus,
underscoring again the criticality of a shared cultural
stance based on factual knowledge and
understanding, on estimates of threat and on
mutuality of expectations.
To be sure, modern diversity, which is widely
admired, carries with it a cultural eclecticism that
challenges collective decisions.
Nevertheless, survival of a humanistic democratic
society basically depends on large numbers of
people making thoughtful, realistic choices, with
the aid of appropriate information.”
(Wenk, Edward, Jr., Margins for Survival, Pergamon Press, ISBN 0-08-023372-4, 1979, pp. 133-134)
Convergence of “Hard” Science and “Soft” Science
We need to be here.
We are here.
T
I
M
E
“Hard” Sciences
• Science
• Technology
• Engineering
• Math
Crises continue, decisionmaking is gridlocked, and
sustainability deteriorates.
“Soft” Sciences
• Social
• Psychological
• Economical
• Political
Hard science (technical) decisions are relatively easy to make compared to the soft science (sociological) decisions.
Learning Starts by Pushing Buttons!
Making Decisions from Mash-ups of Data,
Disciplines and Personalities
Top Ten List - Advice
10. Realize what “pushing that button” actually does as well as the ramifications of
pushing it.
9. Don’t stop learning once you’ve mastered a routine of pushing the buttons.
8. Realize that different users have different needs for different levels of accuracy.
7. Realize that different users have different perceptions of reality and cartography.
6. Don’t duck metadata.
5. Learn to appreciate other perspectives and perceptions.
4. Learn to respect other opinions.
3. Avoid the gravity holes of short-term expediency and maintaining the status quo.
2. Helping people synthesize informed decisions is the essence of education.
1. Strive to understand the relationship between a feature’s measurement, its
purpose on the map and how the information will be used.
Questions?

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