# All posts by Charles D. Ghilani

## Error Ellipses

Part 2: Components and Increasing Probability In the previous article (April 2017) I discuss the correlation of the coordinate values for a station and how an error ellipse is used to determine the direction of the largest error at a station. In this article I review the components of an error ellipse, the process that...

## Part 1: Foundations for Computing Error Ellipses

Standard Error Rectangle and Error Ellipse What is an error ellipse? One of the advantages of a least-squares adjustment over other methods is that a byproduct of the adjustment is not only the most probable values for the unknown coordinates but also standard deviations on these values Suppose for a moment that we are computing...

## Methods of Analyzing Data Part 3: Data Snooping & the tau Criterion

In previous articles, I discuss two rudimentary techniques that can be used to identify blunders in data. However, anyone who has used an advanced least squares adjustment package knows that such software often uses a post-adjustment statistic known as the tau criterion. The tau criterion is a modification of a method known as data snooping,...

## Methods of Analyzing Data, Part 2: Blunders!

Elementary Statistical Procedures  In this article, I assume that a least squares adjustment has been performed. Unfortunately, many novices believe that their work is done because they now have a solution to the unknown station coordinates. However, nothing is farther from the truth. It is at this point that the real work begins in analyzing...

## Methods of Analyzing Data, Part 1

Identifying Blunders with Graphics Mistakes and blunders are an inevitable part of being human. In fact, a wise person once told me that the only people who don’t make mistakes are those who don’t do anything. Because a least squares adjustment of a plane survey is nonlinear, it will not arrive at a solution if...

## What Is a Least Squares Adjustment Anyway?

Up to now I have talked about a least squares adjustment as if everyone knows what it involves. In this article, I discuss what a least squares adjustment is and what makes it so valuable in adjusting observational data. Note: Please click on the images below to see them or read our full issue to...