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.

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 * http://www.anymeeting.com/tgadgets/EC51DA87854B ** - Sharepoint Site – Datum Webinars *** - This Webinar Sharepoint Site – Datum Webinars

Topics Esri projection engine Coordinate systems Transformations Future work Review

Esri Projection Engine

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

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

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

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 10.1.1

Coordinate Systems

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

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 10.1.2

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

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

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

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

Coordinate System Demonstration Demos ArcMap World/Alaska data 1. ArcMap coordinate systems (Do a search for 26906 – 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

Transformations

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.

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.

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

Combined transformations

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

Transformation metadata Areas of use Accuracy C:\Program Files\ArcGIS\Desktop10.1\Documentation\ geographic_transformations.pdf http://support.esri.com/en/knowledgebase/techarticles/detail/21327

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

Transformations with same parameters (1) Officially, NAD83 (CORS96) to ITRF96* NAD_1983_To_WGS_1984_5* NAD_1983_HARN_To_WGS_1984_3 Source: http://geodesy.noaa.gov/CORS/coord_info/ coordtrans_no_support_tables.shtml *Paper: http://www.ngs.noaa.gov/CORS/Articles/SolerSnayASCE.pdf Table 1, page, 51, Last column _5 is Default for DNRGPS And ArcGIS prior to 10.0

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: http://geodesy.noaa.gov/CORS/coord_info/ coordtrans_no_support_tables.shtml

NGS CORS past coordinates website http://geodesy.noaa.gov/CORS/coord_info/coordtrans_no_support_tables.shtml Paper: http://www.ngs.noaa.gov/CORS/Articles/SolerSnayASCE.pdf Table 2, page, 52

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: http://www.ngs.noaa.gov/CORS/coords.shtml

NGS CORS coordinates website http://www.ngs.noaa.gov/CORS/coords.shtml

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

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

Current and Future Work

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

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

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

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

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

Review

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

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

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

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

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.

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), 49-55. http://www.ngs.noaa.gov/CORS/Articles/SolerSnayASCE.pdf Trimble, “GPS Pathfinder Office Software or the GPS Analyst Extension: Resolving the NAD 83 Datum Transformation Issue,” [online]. http://trl.trimble.com/docushare/dsweb/Get/Document- 170369/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 http://support.esri.com/en/knowledgebase/techarticles/detail/ 21327

Questions?

Thank you!