The single most common reason a Christchurch CAT sheet can't be processed is the wrong vertical datum. Read this first.

This is the most technical part of the job, but the core rules are simple once you know them.

The two datums CCC requires

A datum is an agreed reference system for measuring position. You need two: one for horizontal position (where something is on the map) and one for height.

  • Vertical (height) datum: NZVD2016. CCC is unambiguous: "Make sure you're using the NZVD2016 vertical datum. If the old datum is used, we won't be able to process your CAT sheet" (CCC, As-built survey and data requirements). NZVD2016 (New Zealand Vertical Datum 2016) is the official national height datum maintained by Toitū Te Whenua / Land Information New Zealand (LINZ), used "to define heights in New Zealand and its offshore islands" (LINZ, "New Zealand Vertical Datum 2016").
  • Horizontal projection: Mt Pleasant 2000 (NZGD2000). IDS Part 12 states: "For all supplied geospatial data, use the Mt Pleasant 2000 projection, New Zealand Geodetic Datum 2000 (NZGD2000)" (CCC, IDS Part 12). The SAG repeats this: "these are in Mt Pleasant 2000 projection (New Zealand Geodetic Datum 2000)." Mt Pleasant 2000 is the local "meridional circuit" projection for the Christchurch area (EPSG:2124), one of New Zealand's 28 circuits used for cadastral and local survey work (LINZ, "Meridional circuits").

Why the old datum gets you rejected

Until recently Christchurch used a local height datum called Christchurch Drainage Datum (CDD), in use since 1876. CCC has now retired it: "Christchurch City Council has changed to NZVD2016 as its official vertical datum and should be the only datum used at Christchurch City Council… The Christchurch Drainage Datum benchmark network is no longer being maintained or updated. It is now just for historical reference" (CCC, "Christchurch City Council Benchmarks"). CCC adopted NZVD2016 on 19 August 2024 and states plainly: "Data supplied to Christchurch City Council should only be in NZVD2016" (CCC, "Vertical Datum 2016").

CDD and NZVD2016 are not interchangeable - CDD sits on the Lyttelton 1937 datum with a standard offset of 9.043 m (CCC, "Vertical Datum 2016"). Submit CDD levels labelled as NZVD2016 and your levels will be metres out, so CCC cannot load them. This is reinforced nationally: LINZ made NZVD2016 mandatory for cadastral survey from 1 July 2024 (LINZ, "Obtaining NZVD2016 Heights").

Survey control: use the project benchmarks

The SAG requires that "Every survey as-built is to be completed in terms of the project specific benchmark control (detailed on the construction drawings)" and warns: "Do not source benchmarks from elsewhere as each project is in terms of specific project benchmarks." If a benchmark is destroyed, contact the CCC project manager - don't substitute your own (CCC, Survey As-built Guideline). CCC's current GNSS-derived benchmark network is the July 2019 Network (CCC, "Christchurch City Council Benchmarks").

GNSS, accuracy and "location certainty"

GNSS (Global Navigation Satellite System) is the umbrella term for satellite positioning - GPS is one such system. GNSS observations naturally produce an ellipsoidal height in terms of NZGD2000; you convert that to an NZVD2016 height by applying the geoid model (NZGeoid2016), which LINZ's tools do for you (LINZ, "Obtaining NZVD2016 Heights").

The SAG sets accuracy tolerances and an important caveat. For "Survey Accurate" assets the required tolerances are tight - for example pipe inverts to ±50 mm horizontally and ±10 mm in height, and manhole lids/bases to ±100 mm horizontally and ±30 mm in height - and the SAG explicitly notes: "these accuracies cannot be reached using GPS devices" (CCC, Survey As-built Guideline, Table 10). In other words, standalone GNSS isn't enough for inverts and chamber levels; conventional survey methods are needed.

Where an asset genuinely can't be reached (e.g. directional-drilled pipe with no accessible ends, lined pipe with no manhole access), the SAG allows a looser "Approximate" category - but you must set the "Location Certainty" attribute accordingly and justify it in the survey report (CCC, Survey As-built Guideline).

Tools that help

LINZ provides a free online coordinate converter (Concord) to convert between NZ datums, projections and height systems - useful for sanity-checking which datum your data is in (LINZ, geodesy.linz.govt.nz/concord). CCC also points contractors to its "Making the move to the National Vertical Datum" story map and its benchmarks page (CCC, As-built survey and data requirements).

Sources & links