NZ Aerial Surveys Data Dictionary

Table of Contents:

Introduction

Purpose

This document provides detailed metadata (data dictionary) for New Zealand aerial surveys data published on the LINZ Data Service (LDS).

The aerial surveys data includes NZ Imagery Survey Index and NZ Elevation Survey Index.

Background

Over the next decade, the LINZ Topographic Office is working towards its vision of recognising the way location information can help unlock new patterns and knowledge, particularly when it is combined with other types of information. One of our strategic goals is to improve national scale datasets and maximise their opportunities for reuse by a variety of national and regional stakeholders.

Orthoimagery available on the LDS is a result of many different aerial flights spanning many different regions, flown over multiple years, and at different resolutions. As a result, each set of orthoimagery has an index tile dataset which contains metadata specific for that dataset. The NZ Imagery Survey Index data described here provides a single source for all currently available orthoimagery index tiles available on the LDS.

Elevation data available on the LDS is made up of many different regions with separate elevation index tiles including limited metadata. The NZ Elevation Survey Index dataset provides much more information about the elevation surveys in one location.

Description

The NZ Imagery Survey Index dataset provides an index to all orthophoto index tiles found on the LDS. Each record in the dataset provides both a geometry of the maximum extent of the orthophoto index, as well as all attributes found in each index tile. This dataset therefore provides information to assess orthophoto coverage and metadata across the entire country.

The NZ Elevation Survey Index dataset provides an index to all LiDAR derived elevation datasets found on the LDS. Each record in the dataset provides both a geometry of the extent of the elevation survey, as well as useful metadata attributes. The extents are derived from the maximum extent of DEM and DSM coverage and consist of full NZTopo50 1k tiles, even where a tile is only partially covered with data. These extents only provide a rough indication of corresponding point cloud coverage which can be quite different for some elevation surveys.

File format

The dataset consists of vector polygons in NZTM projection.

Definitions

Term Description
DEM Digital Elevation Model. Uniformly spaced bare-earth elevation model, devoid of vegetation and man-made structures.
DSM Digital Surface Model. Uniformly spaced elevation model that depicts the highest surface, including vegetation and man-made structures.
LDS LINZ Data Service
LiDAR Light Detection And Ranging. Remote sensing method to determine distance by emitting pulses of light and timing their reflection.
NZTopo50 1k tiles 1:1,000 nominal scale NZTopo50 subtiles, used to spatially reference elevation data.
Orthophoto An aerial photograph or image geometrically corrected such that the scale is uniform for measuring distances, and has been adjusted for topographic relief, lens distortion, or camera tilt.

Published Data

The data described below represents aerial surveys data openly available on the LINZ Data Service:

Schema: aerial_lds

Description: This schema contains datasets related to aerial surveys to be published on the LINZ Data Service.

Table: nz_imagery_survey_index

Description: This table holds the standardised attributes of aerial imagery surveys. These attributes were previously only contained within individual index tile layers with differing column names and data types.

Column Name Data Type Length Precision Scale Allows Nulls Description
imagery_survey_id integer 32     Yes Unique identifier for the aerial_lds.nz_imagery_survey_index table.
name varchar 100     No The corresponding aerial imagery layer name in the LINZ Data Service.
imagery_id integer 32     Yes Foreign key to the aerial imagery layer identifier in the LINZ Data Service.
index_id integer 32     Yes Foreign key to the index tile layer identifier in the LINZ Data Service.
set_order integer 32     Yes The order that an aerial photograph displays within the NZ Aerial Imageryset. A null value indicates that the aerial photograph is not part of the set.
ground_sample_distance numeric   6 4 Yes Ground sample distance in metres.
accuracy varchar 100     Yes The overall accuracy of the imagery survey. This may contain aggregated accuracy values if accuracy varied throughout the survey. Refer to the related index tile layer for specific accuracies.
supplier varchar 80     Yes The organisation that supplied the aerial imagery.
licensor varchar 250     Yes The organisation that licenses the aerial imagery.
flown_from date       Yes The earliest date on which aerial photographs were taken as part of this imagery survey.
flown_to date       Yes The latest date on which aerial photographs were taken as part of this imagery survey.
shape geometry       Yes A dissolved multipart boundary of the coverage of the imagery survey.

Table: nz_elevation_survey_index

Description: This table holds the standardised attributes of aerial elevation surveys.

Column Name Data Type Length Precision Scale Allows Nulls Description
elevation_survey_id integer 32     Yes Unique identifier for the aerial_lds.nz_elevation_survey_index table.
name varchar 100     No The corresponding aerial elevation layer name in the LINZ Data Service.
index_id integer 32     Yes Foreign key to the index tile layer identifier in the LINZ Data Service.
dem_id integer 32     Yes Foreign key to the DEM layer identifier in the LINZ Data Service.
dsm_id integer 32     Yes Foreign key to the DSM layer identifier in the LINZ Data Service.
point_cloud_doi varchar 50     Yes Foreign key to the point cloud data identifier in Digital Object Identifyer https://doi.org
point_density varchar 50     Yes The point density of the elevation survey.
vertical_datum varchar 20     No The vertical datum of the elevation survey.
horizontal_datum varchar 20     No The horizontal datum of the elevation survey.
supplier varchar 200     No The organisation that supplied the aerial elevation.
licensor varchar 200     No The organisation that licenses the aerial elevation.
flown_from date       Yes The earliest date on which aerial elevations were taken as part of this elevation survey.
flown_to date       Yes The latest date on which aerial elevations were taken as part of this elevation survey.
shape geometry       Yes A dissolved multipart boundary of the coverage of the elevation survey.