Data Supply Metadata s1

Project Airborne LiDAR survey of Napier - 2014 14.035

Client Napier City Council

Client Contact

Ian Tidy

Summary of Data

NZ Aerial Mapping collected airborne LiDAR of the territory of Napier City.

The data was processed into point cloud and terrain model digital map data

products. The supplied dataset is made up of the following items:

• Project extent and layout data

• Classified Point Cloud

• Contours

• Intensity Images

• Orthophotos

Please refer to section Product Generation and Data Supply in this report for

details on these products.

Data Acquisition

The project extent is those described in the Bentley DGN file layout and ESRI

shape file extent that accompanies this dataset. A map showing this area of

interest is also included in Appendix A.

The LiDAR and digital imagery was acquired on 29 June 2014 using NZAM’s

an Optech H300 LiDAR (13SEN328) and Optech CS 10000 camera (001) sensor

system.

The data was collected flying 1,600 metres above lowest ground, and using a

scan field of view of 32 degrees. The outgoing laser pulse rate (PRF) was set

at 150kHZ and mirror scan frequency 47 Hz. The settings were selected to

create a dataset with a minimum 2 point per square meter pulse density in

open ground.

NZAM used LINZ continuously operating reference station HAST for the

source of GNSS base station data during the aerial data acquisition.

Independent of the aerial survey work Opus International Consultants field

surveyed a series of topographic features in open ground, to be later used to

verify the accuracy of the processed ground dataset. This field survey work

was conducted on 17 July and 6 August 2014. The field survey work is in

terms of various LINZ geodetic marks which are detailed in Appendix B.

Data Processing

The LiDAR sensor positioning and orientation (POS) was determined using

the acquired GPS/IMU datasets and Applanix POSPac software. This work

was all undertaken in NZGD2000 geodetic reference system. The data

collected at the LINZ continuously operating reference station was used for

differential GNSS data processing.

The POS data was combined with the LiDAR range files and used to generate

LiDAR point clouds in Hawkes Bay 2000 Transverse Mercator (HB2000) map

projection. This process was undertaken using Optech LiDAR Mapping Suite

software. As well as creating the point clouds this software also checks the

relative fit between points in the individual swath overlap areas. All

subsequent point cloud data processing steps were undertaken using

TerraSolid’s LiDAR processing software modules TerraScan, TerraPhoto and

TerraModeler.

The point cloud was checked for completeness of project coverage and pulse

density. Automated routines tailored to the projects land cover and terrain

were then setup and run on the data to create a ground classified point cloud.

This data was converted from ellipsoidal heights to Napier 1962 vertical

datum using the LINZ NZGeoid09 grid and offset model.

The CS 10000 camera images were developed into 8 bit per channel

uncompressed TIFF format images. The LiDAR POS data was transformed

for use with the camera, and this data was used with the automated classified

ground LiDAR point cloud data to produce the orthophotos with a ground

sample distance of 0.20m.

Comprehensive manual editing of the LiDAR point cloud data was

undertaken to improve the quality of the automatically classified ground

point dataset. This editing involved visually checking over the data and

changing the classification of points into and out of the ground point and

bridge point classes. The orthophotos were used as references to assist with

the editing decision making. During editing LiDAR returns from water

bodies were removed from the ground point dataset. Breakline features were

mapped around ponds, water bodies, streams and other similar featured to

help with flow enforcement of overland flow modelling. The breakline

features were added to the point cloud as closely spaced synthetic points.

Data Processing

continued

The positional accuracy of the processed data has been checked by overlaying

the Opus field surveyed features on the LiDAR dataset displayed with its

intensity values. The data was found to fit well in position. The height

accuracy of the classified ground points were checked by calculating height

difference statistics between a TIN of the LiDAR ground points and the field

surveyed points. The dataset was localised to account for a small bias

observed between the LiDAR and field surveyed data. The overall standard

deviation statistic for the data is +/-0.06m. The statistics for the data at

individual sites are provided in Appendix B.

The accuracy check results support that the point cloud accuracy

specifications of project of +/-0.30m horizontal and +/-0.10 metres vertical

(clear open ground and 1 sigma confidence level) have been met.

The edited point cloud data was converted from Napier 1962 vertical datum

to Hawkes Bay Local Authority 1972 vertical datum (HBALD 1972) by

applying an offset of +10.000 m to the dataset.

Product Generation & Data Supply

Unless otherwise detailed the data has been supplied in terms of HB2000 map

projection. The vertical datum of the dataset is (HBALD 1972). The point

cloud datasets have been tiled into 960m by 1,440m map tiles that were

provided by Napier City Council to NZAM. A Bentley DGN file and ESRI

shape file containing this tile layout is included in the data supply and these

tiles are also shown on the maps in Appendix A.

The products are stored in the following folder structure:

Product Generation & Data Supply

continued

The folder Contours contains 0.5m interval contour datasets. These contours

were generated by interpolation from a TIN of formed from selected ground

classified LiDAR points and the synthetic points. The data is in Bentley DGN

andd ESRI 3D Shape polyline file formats. The data in the DGN files are on

levels INDEX and INTER. Every 5th contour interval contour is on the level

INDEX in the DGN files and has the attribute TYPE=INDEX in the shape files.

The shape file format contours are provided in both Hawkes Bay 2000

Transverse Mercator and New Zealand Transverse Mercator map projections.

The LiDAR point cloud produced at completion of the data processing is in

the folder Ground Classified Point Cloud. The data is in LAS file format v1.2.

The LAS file format is a richer data format and as well as class information

each point is tagged with return intensity, return number, number of returns,

scan angle and swath source id. The unclassified points are in class 1, ground

classified points are in class 2, outlier points are in class 7, returns from water

are in class 9, bridges are 12, and the synthetic ground points added to help

with flow enforcement are in class 34.

The folder Ground Point Cloud contains the subset of the of Ground Classified

Points that can be used for the terrain modelling. This data is in LAS file

format v1.2. The files contain the classes 2 – ground and 34 – synthetic

ground.

Product Generation & Data Supply

continued

The folder Intensity Images contains intensity images with 1m GSD created

using the intensity values of the LiDAR points from the processed point cloud

dataset. These images are in TIFF/TFW file format. The intensity images have

an appearance similar to a black and white photo. They show the relative

strength of reflectance of the LiDAR point returns.

The project extent and product tile layout files are in the Layout folder.

The folder Orthophotos contains the orthophotos of the site. The ground

sample distance of the orthophotos is 0.2m. The automated unchecked

orthophoto processing means that there are mosaic line mismatches in the

orthophotos. They are in TIFF/TFW file format.

The folder Unclassified Point Cloud contains a copy of the point cloud dataset

in the state it was before the assigning of the points to different classification

classes begun. The data is in LAS v1.2 file format and the points are all in

class 1 – unclassified.

If you have requirements for more detailed point cloud classifications,

colourisation of the points, and data in other file formats, map projections or

different products please contact NZAM. Our contact details are provided

below.

Observed Exceptions

No quality exceptions have been noted with this dataset.

Supplier NZ Aerial Mapping Ltd

Address

Cnr Warren St and Avenue Rd

PO Box 6

Hastings 4156

New Zealand

Phone 64-6-873 7550

Supplier Contact

Fadia Zein (e-mail: fadia.zein@nzam.com)

Date of Metadata Creation

12 August 2014

Author Tim Farrier

Appendix A: Project Area

Area of interest shown as magenta outline.

Napier LIDAR 2014

Appendix B: Field Surveying/LiDAR Point Cloud comparison

Ground Check Surveying

NZ Aerial Mapping commissioned Opus International Consultants Ltd to

undertake ground check surveying work to support this project.

Surveying was undertaken at seven sites distributed throughout the project

area. The field observations of features and spot heights were performed

using fast-static GNSS baselines to GeoNET continuously operating

reference stations and RKT GNSS observations an each site. At all seven

sites a series of spot heights were measured on a grid pattern across an area

of approximately 25m by 25m. At two of the sites outline of a building was

surveyed.

Sites were surveyed at; Bayview, Onehunga Rd, Westshore, Hospital Hill,

Anderson Park, Taradale and Awatoto. Field measurements were made at

all of these locations on 17 July 2014. The site surveyed at Bayview was

located on slightly loose gravel. On receipt of the ground check surveying

data NZAM requested Opus establishes a site at Bayview that was on more

suitable land cover. The field measurements for that surveying and the

checking of some outlier points in the field surveying data at Anderson Park

was completed on 6 August 2014.

The GeoNET continuously operating reference stations HAST, LEYL and

MCNL were used for the fast-static surveying. The LINZ published

NZGD2000 and ellipsoidal height values were held fixed for these stations.

At each of the check sites between one and three LINZ geodetic marks were

tied to. The table below lists those marks for each site.

Location LINZ marks

Bayview AER5, CUD8, DFB8, DFB9

Onehunga Rd AER3

Westshore CTEG, DK02

Hospital Hill BDA7, A4EK

Anderson Park B884, CRLA

Taradale BCYQ, CUCQ

Awatoto AENP, BDAF

Where possible LINZ marks were selected that had published Napier 1962

vertical datum high order orthometric heights. This was difficult as there

are few of these marks distributed through the project extent.

The LINZ NZGeoid09 grid and offset model was used to convert the

observed ellipsoidal heights into Napier 1962 vertical datum. Gross error

checks were made between the computed heights and the height published

by LINZ. The observed errors of between 5 and 100mm are consistent with

errors observed while surveying around Napier. The orthometric heights

for these marks were computed in the late 1950’s and the marks would have

been subject to considerable displacement in the preceding years.

LiDAR Height Comparison

The height accuracy of the DTM point cloud was checked by calculating

height difference statistics between a TIN of the LiDAR ground points and

the field surveyed points. This calculation was undertaken for each check

site location individually. The table below shows the computed standard

deviation and average statistic for the individual sites.

Location Standard Deviation (m)

Average (m)

Bayview 0.03 -0.01

Onehunga Rd 0.01 -0.02

Westshore 0.02 0.06

Hospital Hill 0.03 0.004

Anderson Park 0.04 -0.09

Taradale 0.02 -0.06

Awatoto 0.02 -0.04

When the statistics from the height comparison differences are computed for

all the sites at once the standard deviation statistic is +/-0.06m and average

0.00m.