A relic of the past, or a beacon for the future? Anselm Haanen, Surveyor-General, and Nic Donnelly, Manager Positioning at Toitū Te Whenua Land Information New Zealand
S
urveyors may have heard that some promi-
was not necessary to install targets over the marks
nent trig beacons have been removed or are
each time they were used.
proposed to be removed at a few sites around
The introduction of electronic distance measuring
the country.
reduced the dependency on pure triangulation,
Some have expressed concern about the removal of beacons and noted that the beacons are one of the few tangible and enduring artefacts that the public
although the beacons were still needed for theodolite observations. However, the biggest change came with the introduction of GNSS technologies.
associates with surveyors.
Survey control marks no longer had to be placed
In many cases they represent the history of sur-
where they were visible over long distances, usually
veying in the area, and sometimes are associated
on the highest points, and beacons were not
with the early pioneer surveyors.
needed for making GNSS measurements.
Surveyors have also indicated they still
GNSS is now used for almost all control
use many of these beacons, and many New
surveys, which are now focused on establish-
Zealanders enjoy using them as reference
ing a dense network of readily accessible
points, including when interpreting maps.
marks – the vast majority without beacons.
The original purpose of trig beacons
Today, surveyors mainly use beacons
was to support triangulation – they
on prominent high points to orient their
reference the ‘trig stations’ under-
surveys, or to check their orientation
neath them.
by comparing the calculated bearing
The national survey control net-
with the orientation obtained from
work was built by triangulation
other means.
from various baselines around
This demand is likely to de-
the country, particularly for
crease over time as theodolite
the development of New
observations diminish and
Zealand Geodetic Datum
GNSS and other technolo-
Beacon Type
1949. The permanent beacons supported the triangulation, as well as other surveys, as it
Number
Two-metre beacon Wooden
22
Metal
585
Unspecified
3780
Four-metre beacon Wooden Metal Unspecified Non-standard beacon TOTAL
Total
gies become increasingly
4387
accurate, reliable and usable in different environments.
1419 245 33 1141 71
71 5877
Types and numbers of beacons. Most of the ‘unspecified’ two-metre beacons are metal and most of the ‘unspecified’ four-metre beacons are wooden.
SURVEYING+SPATIAL
•
Issue 105 June 2021 9
