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!
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