How does Robust calculation mode works and when to use it.
The choice on whether to use a Robust or Non-Robust Calculation Mode comes down to data redundancy and how Delta-Watch processes data. When we say redundancy, we mean we have more than 1 observation to a particular target within our calculation. Ideally the more the better.
ROBUST CALCULATION
In a robust calculation, Delta-Watch will analyze the multiple redundant observations and calculate a weighted average. We have 5 observations; 5.123, 5.125, 5.122, 5.132, 5.124. Based on the accuracy of the instrument and the spread of these data we can see that 5.132 is the outlier. We shouldn’t discard the observation (it has value) but it should not have the same weight as the other observations.
NON-ROBUST CALCULATION
In a non-robust calculation, Delta-Watch will simply calculate an average of the observations; the good the bad and the ugly. They all have the same weight.
So which one should you use? That’s based on you monitoring scheme….
Let’s take a couple of examples:
Project 1 has a single total station where the client wants a reading every 15 minutes. It takes 10 minutes to read all the monitoring and control prisms – one set of observations. One cannot have a weighted average with only one data point. In this instance we would select a non-robust calculation.
Project 2 has a single total station where the client wants a reading once every hour. We schedule a set of observations to be made once every 15 minutes. Every hour we have 4 sets of observations we can use for our calculation so a robust calculation would be the better choice.
Robust is better than non-robust but selection is not as simple as point and click. One has to understand the nature of the system and how many observations can be used to calculate a single epoch. Like money, when it comes to observations and control points, more is always better than less.