1. Projections and Datums within ArcGIS
Melita Kennedy
Blurb:
Melita Kennedy is a senior product engineer who specializes in coordinate systems, map projections, and datum transformations. She’s been with Esri since 1994, and never thought that being a teaching assistant for Ohio State’s Geodetic Science department’s map projections course would lead to her life’s work. She lives an old orange grove house in Highland, California about 6 miles from Esri headquarters in Redlands.

2. 2012 Datum Series Sponsored by GPSMMS Subcommittee
This is the third webinar in a 3-part Series on Datums.
Datum Primer – Dave Doyle*
GPS Software Datums - Joel Cusick / Alison Walker (Nov 18)**
Projections and Datums in ArcGIS – Melita Kennedy (Dec 17)***
Tim Smith Chair; Joel Cusick Co-Chair *
** - Sharepoint Site – Datum Webinars
*** - This Webinar Sharepoint Site – Datum Webinars

3. Topics Esri projection engine Coordinate systems Transformations
Future work
Review

4. Esri Projection Engine

5. Esri projection engine
One universal library for all ESRI products
pe.dll
Not tied to just one product
Improve maintenance/ease of programming
Speed, consistent results, standardization
Accuracy – tight forward/inverse round trips
Must have inversibility
Engine versus Factory

6. PE library sections Engine Factory Objection creation & processing
Transformations
Projections
Math functions
Factory
Predefined objects
Coordinate systems, ellipsoids, units, etc
Well-known ID lookup

7. Number of Objects in PE Factory
10 Angular Unit
57 Linear units
217 Spheroids
15 Prime Meridians
44 Parameters
14 Geographic methods
2 Horizontal methods
9 Vertical methods
74 Projections
607 Datums
635 GCS
1240 Geographic Transforms
3567 PCS
117 Vertical Datums
124 VCS
47 Vertical Transformations
17 Horizontal/Vertical CS
Total = 6796 at 10.0

8. Number of Objects in PE Factory
10 Angular Unit
59 Linear units
218 Spheroids
15 Prime Meridians
44 Parameters
14 Geographic methods
2 Horizontal methods
9 Vertical methods
76 Projections
644 Datums
671 GCS
1375 Geographic Transforms
4289 PCS
126 Vertical Datums
133 VCS
69 Vertical Transformations
17 Horizontal/Vertical CS
Total = 7771 at

9. Coordinate Systems

10. ArcGIS 10.1 coordinate systems
Coordinate system definitions always stored in library
‘prj files’ installed separately
At 10.1 over 5000 files
Now store the folder information in the library
Display a ‘virtual’ directory structure

11. NAD 1983 and variant support
GCS, UTM zones, SPCS zones, Albers
NAD 1983
NAD 1983 HARN
NAD 1983 CORS96
NAD 1983 NSRS2007
NAD 1983 (2011) + UTM zones
State Plane zones in

12. ArcGIS 10.1 coordinate systems
User interface updated
‘Layers’
Listed each layer
Open to see its coordinate system
Now list each coordinate system
Open to see which layers use it

13. create or import coordinate system
spatial filter
favorites
create or import coordinate system
search
well-known ID

14. Coordinate system search and filter
Spatial filter
Current extent
Layer extent (any in the map)
Custom extent
Search/filter by
Name
Only folders that contain matches will be shown
Well-known ID (WKID) aka 4326, 26906

15. Favorites Now visible (and usable) everywhere
Stored in your user profile
C:\Documents and Settings\melita\Application Data\ ESRI\Desktop10.1\ArcMap\Coordinate Systems (Windows XP)
Supports folders
Import coordinate system from
Data
Prj file
NEW

16. Coordinate System Demonstration
Demos
ArcMap
World/Alaska data
1. ArcMap coordinate systems (Do a search for – nad83 utm zone 6N)
Zoom to southern Alaska
Set spatial filter for coordsys to current extent (versus features? – crosses 180 so get most of world)
Show that only handful of UTM zones are visible, only a few GCS, etc. Show North American GCS.
How many (ex. 374 out of 5016)
Under current coordinate system: now list the WKID
Favorites visible everywhere
Can use Import option for a set of custom or locally used coordinate systems.
Right-click a coordinate system to
Add to favorites
Modify
Save to a prj file

17. Transformations

18. Geographic transformations
‘Datum’ transformations
Convert between GCS
Includes unit, prime meridian, and spheroid changes
Defined in a particular direction
All are reversible
A geographic transformation converts between two geographic coordinate systems. You’ll often hear them referred to as ‘datum’ transformations. All transformation methods convert everything that might need to be changed, including the units, prime meridian, and the spheroid. Each transformation is always defined in a particular direction, from “A” to “B”, but are completely reversible.

19. Transformation methods
Equation-based
Molodensky, Abridged Molodensky, Geocentric Translation
Coordinate Frame, Position Vector, Molodensky-Badekas
Longitude Rotation, 2D lat / lon offsets
File-based
NADCON, HARN, NTv2
We support a number of transformation methods. Some are equation-based—everything needed is within the method’s code and the parameters. There are also file-based methods and the offsets must be interpolated. NTv2, which is used in several countries, supports different resolution grids within the same file. That’s one thing to check—are the files available? Sometimes we do not have permission to distribute the files.

20. ArcMap 10.1 transformations
Sorted by applicability
Area of use
Accuracy
Will create compound (two-step) transformations automatically
Ex. NAD_1927_To_NAD_1983_NADCON + NAD_1983_To_WGS_1984_5

21. Combined transformations

22. ArcMap 10.1.1 transformations
NAD_1927_To_NAD_1983_NADCON
ArcMap default
Until
No more default transformations!

23. Transformation metadata
Areas of use
Accuracy
C:\Program Files\ArcGIS\Desktop10.1\Documentation\ geographic_transformations.pdf

24. Methods in Alaska Coordinate Frame NADCON / HARN Equation-based
Seven parameters
3 translations, 3 rotations, 1 scale factor (in XYZ)
NAD_1983_To_WGS_1984_5
WGS_1984_(ITRF00)_To_NAD_1983
NADCON / HARN
File-based
Generally most accurate
NAD_1927_To_NAD_1983_Alaska
No transformations released for current adjustments

25. Transformations with same parameters (1)
Officially, NAD83 (CORS96) to ITRF96*
NAD_1983_To_WGS_1984_5*
NAD_1983_HARN_To_WGS_1984_3
Source: coordtrans_no_support_tables.shtml
*Paper:
Table 1, page, 51, Last column
_5 is Default for DNRGPS
And ArcGIS prior to 10.0

26. Transformations with same parameters (2)
Officially, ITRF00 to NAD83 (CORS96)
ITRF_2000_To_NAD_1983_CORS96
ITRF_2000_To_NAD_1983_HARN
ITRF_2000_To_NAD_1983_2011
WGS_1984_(ITRF00)_To_NAD_1983_HARN
WGS_1984_(ITRF00)_To_NAD_1983_CORS96
WGS_1984_(ITRF00)_To_NAD_1983_2011
WGS_1984_(ITRF00)_To_NAD_1983
Source: coordtrans_no_support_tables.shtml

27. NGS CORS past coordinates website
Paper:
Table 2, page, 52

28. Transformations with same parameters (3)
ITRF08/WGS84 transformations
ITRF_2008_To_NAD_1983_2011
WGS_1984_(ITRF08)_To_NAD_1983_2011
Pacific Plate
ITRF_2008_To_NAD_1983_PA11
WGS_1984_(ITRF08)_To_NAD_1983_PA11
Marianas Plate
ITRF_2008_To_NAD_1983_MA11
WGS_1984_(ITRF08)_To_NAD_1983_MA11
Source:

29. NGS CORS coordinates website

30. Bookkeeping transformations
Parameters are zeroes!
ITRF_2000_To_WGS_1984
NAD_1983_CORS96_To_NAD_1983_HARN
NAD_1983_CORS96_To_NAD_1983_NSRS2007
NAD_1983_CORS96_To_NAD_1983_2011
NAD_1983_HARN_To_NAD_1983_NSRS2007_1
NAD_1983_HARN_To_NAD_1983_2011
NAD_1983_NSRS2007_To_NAD_1983_2011
NAD_1983_NSRS2007_To_WGS_1984_1

31. Geographic Transformation Demonstration
Demos
ArcMap
World/Alaska data
Show that there’s no default transformation
Show list examples
Show Create Custom Geographic Transformation tool

32. Current and Future Work

33. Geodetic features Editing Geoprocessing Tools Advanced Editing toolbar
Lines, circles, and ellipses
Geoprocessing Tools
Bearing Distance to Line
XY to Line
Table to Ellipse
Buffer
Geographic coordinate system
Calculate Grid Convergence Angle

34. Geodetic features Types Measure tool Geodesic
Great circle / great elliptic
Rhumb line / loxodrome
Normal section
Measure tool

35. Future work Vertical transformations Customizable ‘factory’
Limited selection of coordinate systems and transformations
14 parameter (time-based) datum transformations

36. Vertical transformation methods
Vertical Offset
Vertical Offset and Slope
VERTCON
Geoid models
EGM84, EGM96, EGM2008
US geoid models
Generic model/file type for user-defined ones

37. 14 parameter time-based transformation
Base 7 parameters are updated based on velocity values

38. Review

39. SSF COR SHP WGS84/ITRF Sats ITRF00 Base Provider GIS Export Using
Review:Datums Change
WGS84/ITRF
Sats
ITRF00
Base Provider
Export Using
NAD83(CONUS)CORS96
GIS
SSF
COR
SHP

40. How to Do it In Garmin Workflows with DNRGPS (Formerly DNRGarmin)…
Tag all your data as “plain vanilla” “NAD83”
Exported Coordinate System:
Use this POSC Code:
Use this PRJ
Alaska Albers
3338
NAD 1983 Alaska Albers (Meters).prj
UTM Zone 8
26908
NAD 1983 UTM Zone 8N.prj
GCS NAD83
4269 (no projection
GCS NAD 1983.prj

41. How to Do it
In Pathfinder Office, select the Projection file to match the Exported Coordinate System.
Today tag your CORS corrected data to “CORS96” NAD83
Exported Coordinate System:
Use this PRJ File:
Alaska Albers
NAD 1983 (CORS96) Alaska Albers (Meters).prj
UTM Zone 8
NAD 1983 (CORS96) UTM Zone 8N.prj
GCS NAD83
NAD 1983 (CORS96) prj

42. How to Do it
In ArcGIS *Assuming the standards of how the data “got to NAD83” were followed…
Convert from:
Into GCS_NAD_1983_CORS96 use:
GCS_North_American_1983
None
GCS_WGS_1984
Garmin/DNRGPS:
Go Into GCS_NAD83 only
Mapping Grade: WGS_1984_(ITRF00)_To_NAD_1983_CORS96
GCS_North_American_1983_HARN
NAD_1983_CORS96_To_NAD_1983_HARN

43. Conclusions
As spatial references continue to evolve, it is important to understand how such evolution affects the Mapping software that we use for collecting and processing GPS data.
As we navigate to previous GPS datasets or update them (at submeter), it is extremely important to transform properly to get back to the right place
Options in the field and office GPS software can change the spatial reference of the GPS data that we collect.
Esri software options can also change the spatial reference of any GPS data we collect.
Knowing how these changes occur can eliminate much confusion and lead to satisfactory positioning results.

44. References
Soler, T. & R.A. Snay (2004). Transforming positions and velocities between the International Terrestrial Reference Frame of 2000 and North American Datum of 1983, J. Surv. Engrg., ASCE, 130(2),
Trimble, “GPS Pathfinder Office Software or the GPS Analyst Extension: Resolving the NAD 83 Datum Transformation Issue,” [online] /SprtNote_PFOGPSA_NAD83Datum.pdf
Dr. Richard Snay is Retired Manager of the National Continuously Operating Reference Station (CORS) program and a geodesist with the National Geodetic Survey

45. Questions?

46. Thank you!