Projections and Datums within ArcGIS

Melita Kennedy

2012 Datum Series Sponsored by GPSMMS Subcommittee

This is the third webinar in a 3-part Series on Datums.1) Datum Primer – Dave Doyle*2) GPS Software Datums - Joel Cusick / Alison Walker (Nov 18)**3) Projections and Datums in ArcGIS – Melita Kennedy (Dec 17)***

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

Tim Smith Chair; Joel Cusick Co-Chair

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- 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

spatial filter

well-known ID

favorites

search

create or import coordinate system

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

Transformations

Geographic transformations

• ‘Datum’ transformations• Convert between GCS• Includes unit, prime meridian, and spheroid changes• Defined in a particular direction• All are 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

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- 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 websitehttp://geodesy.noaa.gov/CORS/coord_info/coordtrans_no_support_tables.shtmlPaper: http://www.ngs.noaa.gov/CORS/Articles/SolerSnayASCE.pdfTable 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_MA11Source: http://www.ngs.noaa.gov/CORS/coords.shtml

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

Bookkeeping transformationsParameters 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

Current and Future Work

Geodetic features

• Editing- 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- 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

Review:Datums ChangeWGS84/ITRF

Base Provider

SSF

ITRF00

GIS

COR SHP

Sats

Export Using NAD83(CONUS)CORS96

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!