2016 vendor showcase: better our gnss data collection by mel philbrook
TRANSCRIPT
Bettering Our GNSS Data Collection: How Do You Really Know the Accuracy and Precision of Your
GPS/GNSS Field Data?
Mel Philbrook – Applied Geospatial Engineer Manager• 2015 Worldwide Distributor of the Year• Trimble Gold Channel Partner• Over 25 Years Industry Experience
Agenda• Accuracy versus Precision• Common sources of inaccuracy• Know your NADS• What is a Datum Shift?• Question and Answer Period
Accuracy vs. Precision• Accuracy can be defined as the degree or closeness to
which the information on a map matches the values in the real world. Therefore, when we refer to accuracy, we are talking about quality of data and about number of errors contained in a certain dataset. In GIS data, accuracy can be referred to a geographic position, but it can be referred also to attribute, or conceptual accuracy.
• Precision refers how exact is the description of data. Precise data may be inaccurate, because it may be exactly described but inaccurately gathered. (Maybe the GIS Professional made a mistake, or the data was recorded wrongly into the database).
Accuracy vs. Precision
Image A =Is accurate and precise
Image B =Is precise but not accurate
Accuracy vs. Precision
Image C =Is accurate but imprecise
Accuracy vs. Precision
Image D =Is neither precise or accurate
Accuracy vs. Precision
Common sources of added inaccuracy• Where are the satellites?• Know where is your devices antenna?• Position your body for least obstruction
Where are the satellites?
You affect where are my satellites
Where is my antenna?
Understanding your NADS• NAD83 has many realizations
• NAD83 (1986) Original• NAD83 (1992) HARN• NAD83 (1994) CORS• NAD83 (2007)• NAD83 (2011) Epoch 2010.00
What is a datum shift?
In the past we did not have to be concerned with the shift between NAD83 (1986) and WGS84 as introduced in 1987, because the discrepancy easily fell within our overall error budget. NAD83 and WGS84, originally differed by only a centimeter or two. That is no longer true. In their new definitions—NAD83 (2011) and WGS84 (G1762)—differ up to one or two meters within the continental United States
Don’t believe everything you see
Truth Checker SpreadsheetIn the past we did not have to be concerned with the shift between NAD83 (1986) and WGS84 as introduced in 1987, because the discrepancy easily fell within our overall error budget. NAD83 and WGS84, originally differed by only a centimeter or two. That is no longer true. In their new definitions—NAD83 (2011) and WGS84 (G1762)—differ up to one or two meters within the continental United States
Additional ResourcesFrontier Precision Blog on High Accuracy GIShttps://fpimgis.wordpress.com/webinar‐high‐accuracy‐gis/Nightmare on GIS Street: Accuracy, Datums and Geospatial Datahttp://geospatial‐solutions.com/nightmare‐on‐gis‐street‐accuracy‐datums‐and‐geospatial‐data/GPS, GNSS for Geospatial Professionals (Penn State)https://www.e‐education.psu.edu/geog862/node/1804
THANK YOU!
Q&A