Importance of correct capture of observation and node metadata
As part of the e-survey capture process, information is collected about observations and nodes (marks) in the Cadastral Survey Dataset (CSD). Because of the way this information is captured, sometimes incorrect data is introduced into Landonline. This can create difficulties at pre-validation (surveyor) and validation (LINZ).
The observation and node information is used for many purposes, including:
- running automated tests at pre-validation and validation (to check compliance with the Surveyor-General's Rules), and
- assigning coordinate orders and Survey-Accurate Digital Cadastre (SDC) status after a CSD has been approved.
The information collected about observations includes:
- Survey Class (1, 2, 3, 4)
- Bearing Type (Measured, Calculated, Adopted)
- Distance Type (Measured, Calculated, Adopted)
- Equipment Type (GPS, Theodolite and EDM, Unknown)
The information collected about nodes includes:
- Purpose (Origin, Witness, Traverse, Boundary, Natural Boundary)
- Mark Name
- Condition (Reliably Placed/Found, Removed, Destroyed etc)
- Mark Type (Nail, Peg, Plaque etc)
Incorrect capture
Often the fields that capture this metadata are pre-populated by Landonline or other software, based on selections for the previous observation or node. This makes it efficient to capture many observations with identical characteristics, but there is a risk that the field is not changed when it needs to be.
For example, when moving from capturing adopted data to measured data, the Equipment Type should change from 'Unknown' to whatever equipment was used to carry out the survey.
Impact of incorrect capture on pre-validation and validation
If the observation and node metadata is captured incorrectly, several of the automated tests will not run correctly. Depending on the nature of the incorrect capture, this could lead to failures in the pre-validation report. These failures take time to investigate, and need to be discussed in the survey report. If the failure is due to a capture error, then correcting the capture error and re-running pre-validation should resolve the issue.
Example
A mixed cadastral class CSD with two parcels has both parcels captured as Class I. The larger parcel should have had its observations captured as Class III. At pre-validation, Landonline tests both parcels against the Class I accuracy standards and a number of failures are identified in the larger parcel. If the parcel was captured as Class III, the correct test would be applied and these false failures would not occur.
Impact of incorrect capture on coordinate orders
Once a CSD has been approved, LINZ integrates the new data into the cadastre by means of a least squares adjustment. This process assigns orders and SDC status to coordinates. If there are capture errors in the observation and node metadata, the order and SDC status may be inappropriate. Unreliable coordinate orders can make it more difficult for future surveyors working in the area.
Impact of incorrect capture on future fieldwork
If the mark type and/or condition are incorrect, a future surveyor may spend time looking for a mark that is no longer there or cannot be identified using a metal detector.
