Addresses, coordinates and elevation

An issue's position is recorded three ways: a street address for people, a pair of coordinate systems for systems and surveyors, and a ground elevation for context.

The nearest address

When an issue has no address yet, WEXWatch looks one up from the photo's coordinates and fills the field in for you. It tells you it has done so, and the field remains editable.

The lookup returns the nearest addressable point. That is not the same as the responsible property, and along a road corridor it is often a neighbouring address, because kerbs, drains and signs sit between properties rather than at them. Treat the filled-in value as a starting point and correct it where you know better.

Typing in the field offers address suggestions, biased towards the area around the pin, and choosing one replaces the text. Anything you type by hand is kept exactly as you typed it; WEXWatch does not overwrite an address you have entered.

If no address can be found near the pin, the field says so and stays empty for you to fill in. If the lookup fails outright — usually a service configuration problem rather than a missing address — you are told, and you can retry.

Address lookup and suggestions use Google Places, with Google Geocoding used for the reverse lookup where the deployment has been configured for it. Where it has not, a less precise nearby-place lookup is used instead, which is worth knowing if the addresses you are being offered look approximate.

WGS84 and NZTM2000

Two coordinate systems are recorded for every issue.

WGS84 (EPSG:4326) is latitude and longitude, the system GPS receivers and phone cameras use. It is what comes out of the photo's EXIF metadata, and it is what mapping services, Street View and web maps expect. Values look like -37.558, 175.156.

NZTM2000 (EPSG:2193) is New Zealand Transverse Mercator 2000, the national projected coordinate system. It expresses position as an easting and a northing in metres. Values look like E 1800123.4, N 5837654.2.

WEXWatch converts the photo's WGS84 position to NZTM2000 when the issue is created and stores both.

Why both are stored

They answer different questions.

WGS84 is a position on a spheroid, expressed in degrees. A degree of longitude is not a fixed distance, so measuring or comparing distances in degrees is awkward and misleading. It is the right format for interoperability and for anything that consumes a global coordinate.

NZTM2000 is a projection onto a flat grid in metres, so the difference between two eastings is a distance you can use. It is the coordinate system used by LINZ, councils, surveyors and asset systems in New Zealand: if you give an NZTM easting and northing to a surveyor, they can set out from it. It is also what WEXWatch uses for spatial queries such as finding everything within a set number of metres of a point.

Storing both means neither has to be recomputed later, and there is never any doubt about which conversion was applied.

The map you look at is drawn in Web Mercator, which is what allows the LINZ and Google tile services to share one canvas. That is a display detail — the stored positions are unaffected by it.

Elevation

Where it is available, WEXWatch shows the ground elevation at the pin in metres, looked up from Google's elevation data.

It is context, not a survey level. Use it to understand fall and drainage direction, or to sanity-check that a pin is where you think it is. Do not use it as a design or as-built level: it comes from a terrain model, not from a survey of the site, and it describes the ground rather than the top of a kerb or the invert of a pipe.

Elevation is looked up when you view the issue rather than stored with it, so it may be shown as unavailable if the deployment is not configured for elevation lookups. Nothing else is affected when that happens.

Accuracy in practice

Phone GPS is typically accurate to a handful of metres in the open, and worse under trees, beside cuttings, between buildings or immediately after switching the camera on. That is normally good enough to identify which length of kerb or which sump is meant, especially with a photograph attached, but it is not survey accurate.

If exact position matters — a boundary dispute, a setting-out point, a measurement someone will build to — record it properly and note the surveyed value on the issue timeline.