SDC: SURVEY-ACCURATE DIGITAL CADASTRE

Percentage of nodes achieving SDC Status

The proportion of nodes achieving SDC status in an area is dependent on the size of the error ellipses on nodes and between nodes, which is driven by two primary factors:

  • the quality (accuracy) of the observations themselves (eg old observation are less accurate); and
  • the geometrical strength of the observation network used to generate the coordinates. Additional traverse data and boundary ties provide additional bracing that make for a tighter network. Similarly a higher density of control points add strength.

Older observations captured by the Survey Conversion project are assigned lower accuracies than more modern surveys. These are less likely to result in affected nodes achieving SDC status. Also, where parcels have not been converted, the geometrical strength of the network is usually weakened, also resulting in larger error ellipses. Where possible, additional traverse data will have been captured to provide additional strength to overcome such weaknesses.

Figure 1 gives a sample indication of the observation network that was used to generate the coordinate orders and SDC status in terms of the 5th Order control points.

In Survey Conversion Areas (SCAs) with good quality data, the proportion of nodes achieving SDC status usually exceeds 90%. On the other hand, in areas containing mainly very old surveys the proportion is likely to be much less than this. Just because an area has been converted does not mean that most of its nodes have attained SDC status. Survey Conversion merely converts the existing data with its inherent quality, and reflects this in the SDC status. Survey Conversion does not usually solve inconsistencies inherent between surveys or solve related survey definition problems. It simply converts the existing paper-based data and uses it to generate coordinates that reflect the quality of that data.

SDC: Survey-Accurate Digital Cadastre
Assignment of Coordinate Order and SDC Status
Assignment of SDC Status
Application of SDC Status