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LOST IN TRANSFORMATIONWVGIS 2014 Conference
June 2-5, 2014Christine Iksic
Agenda
• Coordinate Sytems Basics – WV SPC• NAD 83 (what?)• 3 Places Where Datums Matter Most• Projections in ESRI• Transformations in ESRI• Datums & VRS Networks• Checking In with NGS – DSWorld
Projections
Coordinate Systems
Coordinate Systems
• Coordinate systems are slippery… even if coordinates precise coordinates difficult to be certain
• Coordinate systems assign a unique “address” to every point on Earth.
• Coordinates are expressed relative to a datum.
Building of a Map
Ellipsoids and Geoids
DatumsProjections
CoordinateSystems
Unprojected
ProjectedUTM
Lat/Long
State Plane
Datums
Datums
A datum specifies the earth-model (ellipsoid), and the origin associated with a particular set of coordinates.It’s a function of a projection. Datums provide the link between the earth and coordinate systems.Without a datum, coordinates have no meaning.There are many datums used worldwide.Only one datum, WGS-84, is global, the rest are regional.
What is a Datum?
What Language is your data speaking in?
NAD 83 What? Who? Huh?
NGS Datasheet
NAD 83 What?
• Rostport, PaYear N (PA SPC) E (PA SPC) Lat Lon
KX2372(2011) 326082.02 1387517.22 40 12 34.82640 079 49 49.31661
KX2372(2007) 326082.04 1387517.17 40 12 34.82655 079 49 49.31730
KX2372(1993) 326082.02 1387517.15 40 12 34.82633 079 49 49.31750
KX2372(1992) 326082.05 1387517.15 40 12 34.82664 079 49 49.31751
KX2372(1986) 326082.80 1387517.41 40 12 34.83413 079 49 49.31433
Why it Matters
Example - WVDOT Geo Spatial Policy“Henceforth, geospatial coordinates are to be collected utilizing technology capable of a 1-meter level of accuracy. .Techniques such as GPS or conventional surveying should be used to obtain positions at accuracies greater than 1 meter. GPS should be used to obtain positions at the highest possible accuracy.. The recommended standard for representing and reporting geospatial data is as follows”
http://www.transportation.wv.gov/highways/programplanning/planning/grant_administration/wvtrails/Pages/gps.aspx
Datum Shifts
NAD27 Coordinates = 350m, 650m
Map CornerNAD27
4789
541
4790
542
650m
350m
Map Corner
NAD83
NAD83 Coordinates = 150m, 610m
610m
150m
4789
541
4790
542
Datum Shift
WGS 84 NAD 83 (2011) NAD 271 meter1 meter 10 – 120+ meters10 – 120+ meters
How Much?
∆N ∆E total dist
difference 86-11 0.78 0.19 0.80 US Survey Feet
difference 86-92 0.75 0.27 0.80
difference 92-93 0.03 0.00 0.03
difference 93-07 -0.02 -0.02 0.03
difference 07-11 0.02 -0.05 0.06
NAD 83 – Which One?
• WHY the difference, WHAT changed? Epochs = Adjustments
• NAD83 or NAD83 CONUS = 1986 adjustment included NO GPS
• NAD83 HARN = 1992-1993 adjustment were High Accuracy Reference Network (HARN); done state by state; differences between border areas
• NAD83 CONUS CORS 96 - passive• NAD83 (NSRS2007) = 2007 adjustment GPS data only• NAD83 (2001)= 2011 adjustment CORS stations
readjusted and held fixed as primary control
GPS & CLASSICAL ADJUSTMENTS COMPLETED
GPS ADJUSTMENT COMPLETED
1990
-GPS
170
1990-GPS120
1991GPS222
1992GPS366
1997GPS11791992
GPS412
1992 GPS3831992
GPS450
1992GPS419
1992GPS394
1992GPS341
1993
1993
GPS585
1993 GPS667
1992GPS376
1995GPS887
1997.
GPS577
1991GPS197
GPS2601991
1995GPS908
GPS610
1993
GPS725
HPGN/HARN & STATEWIDE NETWORK STATUS
1993
1994GPS404
GPS611
1994GPS633
1991 GP S291 reobs 9/97
1994 GPS721
reos 7/96 GPS1047
reos 1/96 GPS936
1997GPS1133
reos-6/95-GPS904
1995GPS852
1995GPS882
1993GPS606
1996GPS1048 1996
GPS8051996GPS941 1994
GPS7301996GPS1121
1997GPS1178
1997 GPS 12001997
GPS1150
reos-1996
Where Datums Matter
• ESRI 1. Data Frame Properties2. Geodatabase / Layers
• Trimble (other GPS)3. GPS
a. Autonomous vs. Differential CorrectionArcPadArcMobileTerraSync, TerraFlex, others
Transformations & Projections
• Esri provides form controls for selecting the coordinate system (geographic or projected) for a feature class and also for the data frame of a map document in ArcMap and ArcCatalog. When the datums differ, you are prompted for a datum transformation in ArcMap.
• Data Frame – select projection (prj)• Layers – define projection (prj)
Projections – ESRI 10.1 newer
Transformations
What do you select, Yes, No, or Transformations?
Transformations
• Defined in one direction but are inversible – use in either direction.
• _1, _2,_3, _4, _5 indicates ordered they were defined.
• _5 most common to CONUS• Select correct transformation everytime.• Prior to 10.1 ESRI had no transformation
available to NAD83 CORS 96 or 2011. NAD83 HARN was the closest. Today ESRI is current with NGS.
Transformations
From Layers Datum
To Data Fram Datum
Where Datums Matter
• Trimble (other GPS)3. GPS - Autonomous, WAAS, or VRS each field software has slightly different workflow.
a. ArcPad b. ArcMobile
http://positionsblog.trimble.com/?p=234
c. TerraSync, TerraFlex, othersTodays Demo / Instruction
GPS Datums
• Autonomous GPS = WGS84 ITRF 00• Differential Correction or VRS Real Time
Correction will shift data to the reference frame and datum of correction source. Verify!
• WVVRS and KeyNetGPS both NAD83 2011VRS = NAD83 2011
WAAS or Autonomous GPS = WGS84
GPS Settings – Autonomous or WAAS
• Autonomous GPS = WGS84 ITRF 00• No matter what you set coordinate system to
in collector raw data in file is WGS84 ITRF00
GPS w/ VRS or Real Time Correction
• Differentially corrected GPS data are always in terms of the corrections source’s reference frame.
• WVVRS and KeyNetGPS both NAD83 2011• You can change the datum of your data depending
on the settings under real time settings!!• In order to read NAD83 2011 from the collector
both the Real Time Settings Datum & Coordinate System Datum must be NAD83 (CONUS) i.e a 0 transformation
Demo
Live TerraSync DemoSetup
Coordinate SystemReal-Time Settings
Checking In
• Verification of accuracy is essential to gain confidence
• DSWorld – NGS use this NGS software to find datasheets with Google Earth.
• DSWorld – link to download• Know your coordinates• Know the language your data is speaking
Post-Processing
• Differentially corrected GPS data are always in terms of the corrections source’s reference frame.
• Verify reference frame of differential source• Two options
1. Base Provider Properties = WGS84 / ITRF002. Base File (CORS) = NAD 83 (2011)
Exporting
• Exporting a shapefile requires an ESRI .prj file be selected.
• 10.1 prj files aren’t automatically accessible• Save prj file in ESRI to Favorites• Browse to ESRI Favorites in PFO to find prj file.• Select the correct datum! • A transformation can/typically occurs here on
export based on datum selected• ITRF to NAD83 2011
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• Since our Reference Frame is CORS – Base Provider Properties
• Our GPS data is corrected against a source that is in WGS84 or ITRF00
• Export to State Plane NAD83 (2011) / Select Correct prj file
• And our GIS is in NAD83(1986) or CONUS or just NAD83
• We therefore define an NAD83 (2011) to NAD83 CONUS Transformation
• If GIS is in WGS84 define a transformation from NAD 83 (2011) to WGS 84 (00)
Common PP Workflow
Demo
Pathfinder OfficeDifferential Correction
Base Provider or Base File OptionExport to proper datum
Select .prj fileSave prj file to Favorites in ESRI 10.1 or 10.2
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Reference Frames
• CORS Post Process = ITRF00 = WGS84• Autonomous GPS = WGS84 = ITRF00• WAAS = ITRF00 = WGS84
• NDGPS (Radio DGPS) = NAD83 (CORS96)• OMNISTAR (Satellite DGPS) = NAD83 (CORS96)• VRS (most) = NAD83 (2011)
Reference Frames
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Review• Identify the proper reference frame for different differential
sources – VRS and Post-Processing
• Learn how to apply the correct datum transformation inside the GPS and back in the GIS.
• Was there a correction or export, was there a transformation applied?
• Does the prj file match the actual data (not always right.)
• Tell ESRI what transformation to use. Don’t click YES.
• Ask and Tell NAD 83 WHAT???!!!!
• NAD83 (2011) ≠ WGS84about 4.3 feet
Review
Coordinate System?Datum?
Coordinate System?Datum?
DON’T GET LOST in TRANSFORMATION
