# Presentation: 582344

## Datums & Coordinate Systems

- Revenge of the *Shift*

- NAD27 Datum

**Notes:**
Joel.
After Post Field 1 Export.
This provides overview of Datums and Coordinate Systems.  Setting the Stage

## Objective

- Identify different datums
- Identify different coordinate systems

**Notes:**
A quick overview of coordinate systems, datums and their relationship with the way you collect data using space-based technologies and align those data with other data in a GIS.

Once we have learned there are differences it will be important in the following days to learn how to Identify what you got and Make it Match

## Setting The Stage

- GPS is rigid – collects one way
- GIS is flexible – designed to share
- #1 reason GPS data doesn’t line up in GIS -  coordinate system/datum mismatch
- How do we fix it? – Educate

**Notes:**
Think about it.  GPS really is amazing.  You can spend less than a $100 and take one of these gizmos outside and within moments get coordinates of astounding accuracy (you can also spend $25,000 and get coordinates that are no better, at least for a stand-alone unit).  But realize there is a LOT going on in the background in order to get those final coordinates.

GPS is high tech.  And high tech is complicated.  That’s the way it is.  And that’s really what this presentation is all about.  GPS for consumer use is one thing.  But GPS used to provide professional services is entirely something else.  It is the responsibility of the professional to understand the technology he or she is using to provide professional services. 

GIS is all about sharing information ideally across the continent.  Its an ideal digital melting pot and doesn’t care about what you use.

You should care though when you are using submeter GPS.  This equipment found in this class is not recreational in nature, but designed to submit data of high quality into a GIS for archiving.  Handling data in the submeter range takes good solid techniques.

This is a difficult topic and often the number one reason why maps don’t line up. There’s no pill you can take to learn this stuff, you just have to slog your way through it.

## Coordinate Systems

- Latitude and Longitude
- Universal Transverse Mercator (UTM)

**Notes:**
The two prominent location referencing systems used to make maps.  These are latitude/longitude (Lat/long) and Universal Transverse Mercator (UTM).

## Lat / Long Coordinate SystemLatitude

## Lat / Long Coordinate SystemLongitude

*East*
*longitude*

**Grenwich, England**

## UTM Coordinate Systems

**UTM Coordinate Systems**

- Allows projection of a spherical surface onto a flat surface

- A plane coordinate system to relate the coordinates of points on earth’s curved surface with the coordinates of the same points on a plane or flat surface

**Notes:**
This slide needs work.

## UTM Zones in North America

**UTM Zones in North America**

**Notes:**
Seque,
Because both lat/long and UTM have their axis at an abstract location in space, both are relative to the shape of the Earth, which is represented in a datum.   In mapping, datums represent the point or line of reference that is used as a starting location for measurement.  As our understanding of the shape of the Earth has changed, the frame of reference (i.e. datum) for mapping has changed, and the “starting point” from which we measure has changed as well.

## “Figure” of the Earth

**“****Figure” of the Earth**

**Best-fit ellipsoid**
- (e.g., GRS-80, WGS-84)

**Notes:**
The Figure of the earth:
The globe is kinda squished, Its lumpy and irregular in shape but we have to assign something simple to define this squished shape.  We call this an ellipsoid.  Both LAT/Long and UTM are relative to the shape of the Earth, which is represented by a datum.

## Datum and Ellipsoids

- Datum - represented by ellipsoid
- Reference ellipsoid examples:
- Clarke 1866
- GRS 80
- WGS 84

## Common Geographic Datums

- NAD27
- NAD83
- WGS84
- ITRF00

**Notes:**
In the US, GIS personnel are most likely to encounter three horizontal reference map DatumsNAD27
NAD83
WGS84
ITRF00 – Global geodetic system used mainly in scientific studies.

## NAD27: 	Clarke 1866 ellipsoid			origin in Kansas

- Datum Origin on Surface of Earth

- Ellipsoid Model based on less precise surveys

**Notes:**
As I see it, NAD27’s biggest problem is that the datum origin is on the surface of the earth and it’s second biggest problem is that the Clark 1866 ellipsoid just doesn’t work as you leave the vicinity of Meades Ranch.  Be careful,  the diagram looks like you’re saying NAD27 is ECEF.  

## NAD27:  Leaving Behind 

- Invented Space Travel
- Increasing accuracy of surveys
- Shift from optical surveys to a mathematical model of the Earths shape
- The result is a specific point on the landscape can take on multiple meanings

**Notes:**
So over time, as we invented space travel, increased accuracy of surveying the science of mapping our earth shifted from optical surveys to a mathematical model of the Earths shape.  The result is that any specific point on the earth can take on multiple meanings.

## GPS Datum:  WGS 84

- Origin is at the Earth’s center of mass (geocentric)
- This is the datum used for the _NAVSTAR GPS_ satellites

## WGS84:	WGS84 ellipsoid			origin center of earth

**WGS84:****	****WGS84 ellipsoid****	****	****	****origin center of earth**

- The origins of the WGS84 and NAD83 ellipsoids are at the center of the earth’s mass, which makes them ideal for a GPS datum

## Datum Adjustments

- Known as Datum Adjustments or Epochs
- WGS84 (G1150) – most current version
- “Original” NAD83 = NAD83 (1986)
- NAD83 (1992)
- NAD83 (2002)
- ......
- Most Current NAD83
- NAD83 (CORS96) (Epoch 2003.00)

**Notes:**
Just when you thought all you had to learn was a Datum name like WGS84...
It’s a bit more complicated.  As a datum is more precicesly defined or datums become adjusted over time as we learn more about the center of the earths mass.  Satellite, gravity measurements all enhance the level of precision that we can measure things.  Datums therefore are adjusted or realized using the term epochs.  These datum reference frames are noted by a year (1986) or (1992).

Whats happened is that the most current realization of NAD83 and WGS84 differ by up to a meter.  Errors can be introduced into a map by assuming these are the same

## Over Time Datums Have Grown Apart

- NAD83 = WGS84

- WGS84

- NAD83

- ~4+ feet

**Notes:**
This slide works great.  Shows the old and new (1986 what we knew then) and What we know now.

Do Note:  at an even deeper level is that NAD83 has kept up with WGS84 as well.  It’s just that this slide is a bit misleading, that there is not a NAD83 next to the modern WGS84.  It is,,,, its called NAD83(CONUS) CORS96.

## Differences between Datums

- NAD27 ≠ NAD83 (1986)

- NAD27 Datum

- 33 to 700 feet

**Notes:**
Many of you have seen these large differences between the older NAD27 and NAD83.  Alaskan’s are often caught with seeing shifts exceed two football fields.

## Shift Happens - Redmond OR 2005 Example

**710 Feet**

**Notes:**
Here is the shift in the GIS. 
GIS baselayers are in NAD83.  When a person transfers GPS data using PFO to GIS without switching to NAD83, then this Northern Displacement occurs – 710 Feet.  

This causes confusion, delay and loss of confidence in Fire field and GIS staff.

## Differences between Datums

- WGS84 = ITRF00
- 		 about 2cm
- NAD83 (CORS96) **≠**** **WGS84
- 		about 4.3 feet

- For Arcata

**Notes:**
More subtle differences or error shifts can be seen here though when Errors can be introduced into a map by assuming these are the same

## Reference Frames

- Differentially corrected GPS data are always in terms of the corrections source’s reference frame.
- In Arcata we are using CORS station data and therefore must apply the correct datum transform between the GPS data and your GIS

## Mapping / Coordinate System

- For Arcata BLM Office in Pathfinder Office

- Accuracy Test on Friday

**	**_**Coordinate System:**_**	****UTM Zone 10N**
**  **_**Datum:**_**	****     NAD 83 (CONUS) CORS96**

## Reason Were Using NAD83 (CONUS) CORS96

- GIS In NAD83
- Using CORS96

- CORS
- ITRF00

- ~4+ feet

## When Do Datums/Coordinate Systems Matter?

- PFO Map View
- Coordinate system
- Terrasync
- Coordinate System
- Export Utility
- Shape Export Coordinate System
- ArcGIS Catalog
- Define Projection
- ArcGIS
- Data Frame Properties – Coordinate System Tab

**Notes:**
If we had to break the Datum shift issue into two areas where it matters most, its in the Field and in the GIS.

In the field when communicating between GPS users and when communicating or transferring data between GPS and paper maps.  The classic example here is the dispatcher is in one datum and you, the user is in another datum.  

In the GIS, after the data is stored and transferred into a Geographic Information system like arcView.

Projecting data on top of GIS data based in a different datum and/or coordinate system.  The data is shifted relative to the base layers.  This is a very common occurrence and can prove disastrous when the map is printed out the next day with the fire depicted on the wrong side of the road or the safety zone is in the wrong place.  The GIST making the map never had the chance to visit the site, so confirmation of the data was impossible.

## GPS Datum Tips

- Summary:
- Check, check, check
- ASK your GIS Specialist
- Good handouts in <cd>/references

## Conclusion

- Now that you’ve learned there are differences it will be important that you learn how to...
- Make it Match
- Pre-Field Day 2
- Datum Transforms
- Friday’s Test against Truth

**Notes:**
The tools you are going to learn in these three days will give you the capability to set the appropriate export settings in PFO to match the coordinate system and datum of your GIS.
You Just learned there are differences.
You will be learning 
How to Check (identify the coordinate/datum) 
Make the Data Match

## You are here

**You are here**

## Matching Datums

- Revenge of the *Shift*

- I use GPS for all my mapping.  I’m using NAD83(1986)

- I’m using WGS84

- 4.3 ft

**Notes:**
Joels.
A short reiteration to always check.  This is prior to transferring an image to the datalogger on Pre-Field 2.  This was dropped in Arcata due to time constraints.  

## Objective

**Objective**

- Overview of Matching Datums and Coordinate Systems in Pathfinder Office and Data Transfer

## Taking “GIS” out in the Field

- Rasters
- Vectors
- All require a projection (coordinate system) defined ahead of time

## Matching Data Steps

- Know what it is – Metadata helps
- Tell Pathfinder Office the correct Datum and Coordinate System

## When Do Datums/Coordinate Systems Matter?

- PFO Map View
- Coordinate system
- Terrasync
- Coordinate System
- Export Utility
- Shape Export Coordinate System
- ArcGIS Catalog
- Define Projection
- ArcGIS
- Data Frame Properties – Coordinate System Tab

**Notes:**
If we had to break the Datum shift issue into two areas where it matters most, its in the Field and in the GIS.

In the field when communicating between GPS users and when communicating or transferring data between GPS and paper maps.  The classic example here is the dispatcher is in one datum and you, the user is in another datum.  

In the GIS, after the data is stored and transferred into a Geographic Information system like arcView.

Projecting data on top of GIS data based in a different datum and/or coordinate system.  The data is shifted relative to the base layers.  This is a very common occurrence and can prove disastrous when the map is printed out the next day with the fire depicted on the wrong side of the road or the safety zone is in the wrong place.  The GIST making the map never had the chance to visit the site, so confirmation of the data was impossible.

## Today’s Background Image

- Humboldt Campus Map
- PDF obtained from Website
- Converted to TIFF
- Co-registered 12 control points between Ortho
- ~ Depending on accuracy of Ortho, maybe +/- 20 meters in horizontal accuracy

## Coordinate Systemand Datum

**	**_**Coordinate System:**_**	****UTM Zone 10N**
**	**_**Datum:**_**	****NAD 83 (CONUS)**

**Notes:**
At the time you obtain image file and world file, find out coordinate system and datum.  If a projection file is available, then open file to find out information. 

## Next Step

- Data Transfer background imagery to the GeoCE device

## You are here

**You are here**

## Datum Transforms

**Datum Transforms**

- Getting it Right in Pathfinder Office

**Notes:**
Joels Datum Part III.
Following Lauras Mapping Tools 3.
Some lecture on Accuracy, reiteration of differences in Datums.  Introduce Reference Frames and walk the class thru a BAD and GOOD Export.

This requires folks to have collected a rover file with some point features on top of NAD83(CORS96) Truth.  Export as BAD, then GOOD.

Pick up in Datum Transform 04B with the Steps in ArcGIS.

## Objective

- Identify the proper reference frame for different differential sources
- Learn how to apply the correct datum transformation inside PFO

## Prior to this Presentation

- You occupied “Truth”
- Collected at least one Point feature
- Now we can compare!

## Mapping Grade GPS Accuracy

- Verification of accuracy is essential to gain confidence
- We have to ensure we transform the data correctly to GIS

## Accuracy Slides

**Accuracy Slides**

- Using Real Data.

## Today is Your Chance to Test

- First Some Background

## NAD83 Developed Using WGS84

**NAD83 Developed Using WGS84**

- The origins of the WGS84 and NAD83 ellipsoids are at the center of the earth’s mass, which makes them ideal for a GPS datum

- Review

## Over Time Datums Have Grown Apart

- NAD83 = WGS84

- WGS84

- NAD83

- ~4+ feet

- Review

## Datum Adjustments

- Known as Datum Adjustments or Epochs
- WGS84 (G1150) – most current version
- Most Current NAD83
- NAD83 (CORS96) (Epoch 2003.00)

- Review

**Notes:**
Just when you thought all you had to learn was a Datum name like WGS84...
It’s a bit more complicated.  As a datum is more precicesly defined or datums become adjusted over time as we learn more about the center of the earths mass.  Satellite, gravity measurements all enhance the level of precision that we can measure things.  Datums therefore are adjusted or realized using the term epochs.  These datum reference frames are noted by a year (1986) or (1992).

Whats happened is that the most current realization of NAD83 and WGS84 differ by up to a meter.  Errors can be introduced into a map by assuming these are the same

## Differences between Datums

- WGS84 = ITRF00
- 		 about 2cm
- NAD83 (CORS96) **≠**** **WGS84
- 		about 4.3 feet

- For Arcata

- Review

**Notes:**
More subtle differences or error shifts can be seen here though when Errors can be introduced into a map by assuming these are the same

## Reference Frames

- CORS Post Process = ITRF00
- Autonomous GPS = WGS84 = ITRF00
- WAAS = ITRF00
- NDGPS (Radio DGPS) = NAD83 (CORS96)
- OMNISTAR (Satellite DGPS) = NAD83 (CORS96)

- Review

## NAD 83 (CORS96) to WGS-84 (G1150)

****

**4.2 ft**

**WGS-84 (G1150)****= ITRF 00 (2001.0)**

**“****TRUTH”****NAD 83 (2003.0)****Anchorage**

***This is essentially the CORS or WAAS Reference Frame***

## Reference

- Locate this support doc and follow along
- 2nd to last reference in Notebook
- _[SprtNote_PFO-GPSA_NAD83Datum.pdf](file:///../References/SprtNote_PFO-GPSA_NAD83Datum.pdf)_

## This Training Used Scenario 2

## Since our Reference Frame is CORS

- Our GPS data is corrected against a source that is in WGS84 or ITRF00
- And our GIS is in NAD83
- We therefore define an ITRF00 to NAD83 Transform

## Export Out as NAD83 (CONUS) CORS96

- The reason behind our class standard

## To Keep Shifts at Bay

**To Keep Shifts at Bay**

- Verify reference frame of differential source

## To Keep Shifts at Bay

- Apply the correct datum transform before the Export depending on your GIS needs

- Talk to your GIS Nerd

## Summary

- Identified the proper reference frame for different differential sources
- Learned how to apply the correct datum transformation inside PFO
- Keep Shifts at Bay by verifying and using the right transform

## If You Use WAAS?

- Since WAAS is ITRF use NAD 1983 (Conus) CORS96

**Notes:**
Extra Slide

## If You Use Coast Guard Beacon?

- Since NDGPS is already in NAD83 (CORS96) use NAD 1983 (Conus)
- No need to apply a                   transform.

**Notes:**
Extra Slide

## You are here

**You are here**