Rules relating to referenced CSDs and bearing corrections
The RCS 2010 require that a CSD must include:
- a list of CSDs used in the determination of the survey. Rule 9.1(a).
- any bearing adjustments applied to each CSD from which a bearing was adopted in the CSD. Rule 9.3(b).
- a survey report that contains the basis for any bearing adjustment applied to an adopted bearing. Rule 8.2(a)(iii).
The term ‘bearing correction’ as used in the Landonline survey header and vector capture of a CSD means the same as ‘bearing adjustment’ in RCS 2010.
Listing the bearing corrections applied to referenced surveys in the survey header and reporting on the basis of any bearing corrections applied to adopted vectors provides confidence that the orientation of the adopted work is in terms of the projection selected for the survey. Rule 4.1.
Bearing corrections in the survey header
It is a requirement to list in the survey header all referenced surveys used in the determination of a CSD. This typically incudes all existing approved CSDs that have been used as an adoption source but can include other relevant CSDs.
The requirement to show a bearing correction in the survey header, under Rule 9.3(b), relates to referenced surveys that have had a bearing correction applied to adopted vectors sourced from those surveys.
It is not necessary to capture a bearing correction in the survey header for referenced surveys that have not had bearings adopted from them. In this instance leaving the bearing correction field blank in the survey header is acceptable.
Showing a bearing correction of 0°00’00” for a referenced survey in the survey header should be avoided if the referenced survey has not been assessed for bearing corrections. This could give the false impression that the orientation of the referenced survey has been considered and is in terms of Rule 4.1(c) when it may not have been evaluated. In this instance showing a ‘blank’ value for the bearing correction is preferable.
Bearing corrections in vector capture
The functionality to capture bearing corrections applied to individual vectors has always been in the Landonline data schema for vectors.
When capturing bearing corrections applied to individual adopted vectors the correction values must agree with the value shown in survey header for the referenced survey unless the differences are adequately explained in the survey report.
A valid reason where a bearing correction for individual vectors may differ from the survey header is when a surveyor has determined differing correction values are required to be applied to separate sets of vectors from the same source CSD. In this rare situation a value that matches the majority of the applied bearing corrections should be shown in the survey header with any different values shown in the mark and vector report. Full justification for the differing corrections is required in the survey report.
Reporting on the basis for bearing corrections applied
The application of Rule 8.2(a)(iii) requires that the survey report must include a clear description of the basis for determining a bearing adjustment, rather than just a statement that a bearing correction has been applied. Any differences between the bearing correction shown in the survey header and the mark and vector report must also be adequately explained.
Whenever reviewing an existing CSD for bearing corrections, it is prudent to independently verify any bearing corrections shown by referring to the survey report for the CSD or by comparison to other source information.
Prepared by: Cadastral Surveyors Group, Property Rights