Spatial -

NOAA Datums Videos 2014

Differential correction with NA2011 and the newest epoch of NAD83

See our and Datums Basics and GPS Tutorials for the long-awaited results of months of rigorous testing and peer review

Trimble Positions software has replaced Trimble GPS Analyst in ArcGIS 10.1

ALASKA GPS and GIS users - check out Joel Cusick's Datum and Projections presentation Feb 2013

ArcGIS 10.1 - New and Cool improvements see Presentation from Melita Kennedy, ESRI : Projections and Datums Dec 2012

Home GPS Tutorials Accuracy REALLY does matter
Accuracy REALLY does matter PDF Print E-mail


Yes , do the Right Thing and pay attention to accuracy at all levels

The accumulation of error as data is repeated analyzed and projected for multiple purposes. Carefully integrate your mapping grade GPS data into a GIS.  M. Dennis makes a strong argument for Doing The Right Thing  and treating data with utmost eye for accuracy. 

1. Historical perspective

In May 2000, deliberate degradation of GPS accuracy (Selective Availability) was turned off.  With this new found accuracy, besides more ‘practical applications’, geocaching was born.  Anyone with GPS and internet connation could ‘hide’ and ‘find’ with recreational GPS. 

2. User expectations have soared

Today we take mapping programs, widely available submeter accurate imagery and online mapping data and resources for granted.  Most mobile devices, cellular phone and even cameras are now GPS enabled. 

3. Do mm and cm  really matter?

The answer depends on your project and your  purpose for collecting the data.  Here are some issues to consider. 

For recreational purposed like finding a geocache or trail. but when combining ‘good enough’ GPS data with other datasets it can.

Mapping grade GPS now offers sub-meter accuracy at a price only once afforded by survey grade technology.  

Also important to think about is what with what other datasets will your project data be analyzed and displayed.  In other words, how do you explain to your users why your ‘good enough’ GPS trail data does not line up with the roads displayed on a Google Earth driving tour which features sub-meter, color imagery?  

Even at 2 cm/yr with adjustment from Epochs 1997 to current 2012, in 15 years shift will be 30 cm total!