OBSERVATION ACCURACY

In Landonline coordinates are generated and maintained by least squares adjustment of survey observations. The least squares technique requires the adjusted observations to have specified accuracy values.

For cadastral surveys, the observation accuracy is automatically determined by Landonline, based on a number of factors, such as:

• The purposes of the marks (eg, boundary, traverse) at each end of the observed line;
• the cadastral class (eg, I, II or III);
• the specified equipment type for the observation;
• the type of observation (eg, bearing or distance); and
• the length of the observed line.

Based on experience with adjusting cadastral survey observations, LINZ has defined accuracy values for different types of survey equipment. For example, with a theodolite and band, the bearings and distances are both of medium accuracy. With a total station, the bearings are medium accuracy and the distances are high accuracy. With GPS, both bearings and distances are high accuracy.

There is also an Unknown equipment type for observations from surveys where the method of measurement is unknown. A proposed new equipment type of Scaled will assign lower accuracy to measurements where the distance has been scaled from a plan and an approximate bearing has been protracted or calculated from scaled positions.

The final observation accuracy values calculated by Landonline and assigned to the observation are derived from a constant component (independent of the length of the line) and a distance dependent component. This allows for long lines to have higher bearing accuracy than short lines.