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 andvalue 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 LDP1. Projected (grid) distances very close to actual (ground) horizontal distances.2. Less distortion over larger areas compared to project sites.3. Reduced convergence angles (assuming central meridian centered in zone).4. Can estimate distortion levels from field topographic elevation for most areas.5. 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 AccuracyClosure:

Traverse Adjustments:Transit Rule, Compass Rule, Crandall MethodLeast Squares Adjustment

Horizontal control accuracy standards for traverse

Errors, Distortions and AccuracyEquipment 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

“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.’”

GIS’t a Little Bit ofGeometrical and Physical Geodesy

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 SystemsEarth-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 SystemsLocal 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 SystemsGeodetic 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.

Plane Surveying Geodetic Surveying (Geodesy)

Transit

Total Station

Global Position System(GPS) Satellite

Survey-Grade GPS Base & Rover

Photogrammetry & Remote Sensing

Traditional Maps→

→

→

→

→

→

3D CADD→

→Mash-Up???

Self-Adjusting Level

Scanner

Assembling Technologies that Span Different Time Periods, Skills and Disciplines

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

“Hard” Sciences • Science• Technology• Engineering• Math

“Soft” Sciences• Social• Psychological• Economical• Political

Hard science (technical) decisions are relatively easy to make compared to the soft science (sociological) decisions.

We need to be here.

We are here.TIME

Crises continue, decision-making is gridlocked, and sustainability deteriorates.

Learning Starts by Pushing Buttons!

Making Decisions from Mash-ups of Data, Disciplines and Personalities

Top Ten List - Advice10. 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?