Transcript Iskic 2014

LOST IN TRANSFORMATION
WVGIS 2014 Conference
June 2-5, 2014
Christine Iksic
Agenda
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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
Projections
Unprojected
Datums
Lat/Long
UTM
Projected
State Plane
Coordinate
Systems
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, Pa
Year
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/programplanni
ng/planning/grant_administration/wvtrails/Pages/gps.aspx
Datum Shifts
4790
4790
350m
150m
650m
4789
4789
610m
Map Corner
NAD27
541541
542542
Map Corner
NAD83
NAD27 Coordinates = 350m, 650m
NAD83 Coordinates = 150m, 610m
Datum Shift
WGS 84
NAD 83 (2011)
1 meter
10 – 120+ meters
NAD 27
How Much?
difference 86-11
∆N
∆E
total dist
0.78
0.19
0.80
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
US Survey Feet
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
NETWORK STATUS
HPGN/HARN & STATEWIDE
1991
GPS222
1996
1992
1991
GPS341
GPS197
reos 7/96
GPS1047
GPS606
1994
GPS404
1992
1993
GPS633
1992
1992
GPS376
1996
1996
GPS805
1991
GP S291
GPS941
1995
reobs 9/97
1996
GPS1121
GPS887
1994
GPS412
GPS1048
GPS730
1995
1997 1997 GPS882
1997
1997 GPS1178
GPS1179
GPS1150
GPS
1200
1993
GPS610
1995
GPS419
1997
1993
GPS852
GPS1133
1992 1994
GPS725
1992
1992
1994
GPS383
GPS366
GPS721
reos 1/96 GPS936
GPS450
1993
GPS667
GPS & CLASSICAL ADJUSTMENTS COMPLETED
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GPS ADJUSTMENT COMPLETED
1997
GPS577
Where Datums Matter
• ESRI
1. Data Frame Properties
2. Geodatabase / Layers
• Trimble (other GPS)
3. GPS
a. Autonomous vs. Differential Correction
ArcPad
ArcMobile
TerraSync, 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, others
Todays 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 2011
VRS = 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 Demo
Setup
Coordinate System
Real-Time Settings
WV VRS
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 / ITRF00
2. 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
Common PP Workflow
• 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)
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Demo
Pathfinder Office
Differential Correction
Base Provider or Base File Option
Export to proper datum
Select .prj file
Save prj file to Favorites in ESRI 10.1 or 10.2
ReferenceReference
Frames 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)
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Review
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) ≠ WGS84
about 4.3 feet
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DON’T GET LOST in TRANSFORMATION
Coordinate System?
Datum?
Questions
Questions
• Christine Iksic
[email protected]
412-512-5665