## Fixit4

### Overview

There are many least squares adjustment programmes. Dr Bruce Harvey of The University of New South Wales has created a least squares adjustment programme called Fixit4. The process of least squares involves setting up a model and then proceeding with a series of matrix operations. The model contains observation equations, partial derivatives and statistics. The observation equations and hence partial derivatives are determined by the type of observations that are being adjusted i.e. height differences, horizontal distances and directions all have different observation equations and partial derivatives.

**Cadastral model in Fixit4**

The above model is the result after a majority of the possible outliers were detected and removed. After this stage a series of investigations and adjustments were done. The results of one are shown below.

### Effect of constraining control

This table represents the differences between a minimally constrained and a fully constrained network. There were 14 points chosen to compare. These were at important places in the network such as intersections and corners.

The differences range in magnitude depending on how connected each point was to a control point being held fixed. The differences all had a common direction.