Special Topics: Lab 9

This week's lab covered vertical accuracy of a DEM.  I used data points on top of the LIDAR layer and used the Extract Values tool.  Once the values were extracted, I had to convert the values from feet to meters.  The next thing was to calculate the difference between the LIDAR values and the field points.  Once the difference was calculated, I squared the difference and then summed it.  The next step was to find the average and then take the square root to find the Root Mean Square Average.

Once the RMSE was calculated, to determine the 95th percentile accuracy, I multiplied the RMSE by 1.96.  To find the 68th percentile accuracy, I multiplied the RMSE by 1.69.  The lower the number, the more accurate it is.  To determine if there was a bias, I had to find the Mean Error.  To find that, I took the sum of the difference and then take the average.  Below are the results.  The results show the most accurate and that the urban area had the most bias.

Accuracy Results