GIS5935 Module 1.1: Accuracy and Precision Fundamentals

 This lab provided us with the opportunity to compare accuracy and precision of (50) points that were collected using a GPS unit.

 

 

Accuracy is the difference between the reference point/true value and the measured point(s)/value(s), while precision refers to how close measured point(s)/value(s) are in relation to one another. 

Horizontal accuracy is determined by calculating the difference in distance between the reference point and (in this case) average waypoint. We used the Measure tool in ArcGIS Pro to determine the distance between these two points (3.27 meters apart).

Horizontal precision in this lab focused on determining waypoints that feel within the 68th percentile from the average waypoint. We determined vertical (elevation) and horizontal points that were within the 68th percentile, as the 68th percentile is the most commonly used measure of precision and indicates the distance within which 68% of observations (points) are. 

The calculated horizontal accuracy value is 1.6 meters. The calculated horizontal precision was 4.8 meters. This appears to be a significant difference (-3.2).

My estimated average elevation was 28.54 m, while the reference point had a reported elevation (reference point) of 22.58 m. The calculated vertical accuracy is 5.96 m (average elevation – reference point elevation). Vertical precision was calculated to be 29.4 m, so there is a significant difference between vertical precision and accuracy. There is difference between my reference values and my resulting value for both vertical and horizonal accuracies & precisions, which indicates bias in my results.  

Metrics: 

·       Average longitude in decimal degrees

o   -82.318845 dd

·       Average latitude in decimal degrees

o   27.825872 dd

·       Average elevation in meters

o   28.542 meters

·       Horizontal precision (68%) in meters

o   4.8 meters

·       Vertical precision (68%) in meters

o   29.4 meters

·       Horizontal accuracy

o   1.6 meters

·       Vertical accuracy

o    5.96 meters


RMSE

Mean

Median

95 Percentile

Min

Max

68 Percentile

90 Percentile

3.06

2.67

2.45

5.69

0.14

6.95

3.18

4.67

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