Flynn, Julian (2017) The use of Nearmap Imagery in Two Dimensional Topographic Surveying Applications. [USQ Project]
Abstract
Aerial imagery has long been used in mapping dating back to the 1800’s (Curtin University, 2008). With the advent of modern aircraft, GPS equipment and high resolution cameras there are vast resources available for acquiring imagery. Some government organisations even provide historical imagery for free. Ultra high resolution imagery produced by Nearmap is available in the most densely populated areas of Australia and updated up to six times a year. The regularity of the updates ensures that the imagery has a high probability of matching a site in its current configuration. Nearmap’s web based platform allows users to navigate to their site and browse current and past imagery at a resolution of 75mm (Nearmap, 2017). Nearmap even states that their imagery is able to be used to produce a detail survey without even leaving the office. This statement along with the accuracy statement can be misinterpreted and taken to mean that they guarantee a level of accuracy over any part of their imagery and that it is fit for inclusion in a topographical survey database. The aim of this dissertation is to provide the spatial community with a meaningful comparison between traditionally surveyed data and data digitised from a Nearmap image and to test the accuracy of that data in order to determine the level of appropriateness of the use of this imagery for the stated purpose. Regardless of the accuracy the imagery is invaluable for other purposes such as providing background information in a topographic survey. Due to Nearmap not releasing their three dimensional mesh to the public yet only the plannimetric accuracy is assessed in this dissertation.
Imagery was output from Nearmap and features within the image were compared to features surveyed traditionally. Additionally a site specific orthophoto was flown by Bennett and Bennett (the author’s employer) which was used in a comparison to the traditionally surveyed. The Nearmap image had a mean of 185mm ±26mm for a point accuracy at the 95% confidence level while the site specific orthophoto had a mean of 44mm ±7mm at the 95% confidence level. Furthermore various discrepancies were observed in the Nearmap image with some joins in images being obvious where line marking didn’t line up. This visual error suggests that the 150mm error may not be the case over the whole of the image. The findings of this dissertation illustrate that the error of the Nearmap image varies a great deal across an image with some points observed being up to 480mm different to the traditionally surveyed location.
The use of vendor specific products or any product with an unknown origin and processing can be dangerous if the accuracy limits are not tested. While the average error estimated by Nearmap was closely achieved, the whole picture told a different story.
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| Item Type: | USQ Project |
|---|---|
| Item Status: | Live Archive |
| Additional Information: | Bachelor of Spatial Science (Honours) (Surveying) |
| Faculty/School / Institute/Centre: | Historic - Faculty of Health, Engineering and Sciences - School of Civil Engineering and Surveying (1 Jul 2013 - 31 Dec 2021) |
| Supervisors: | Paudyal, Dev Raj |
| Date Deposited: | 07 Sep 2022 03:20 |
| Last Modified: | 07 Sep 2022 03:20 |
| Uncontrolled Keywords: | Aerial imagery; Nearmap; comparison |
| URI: | https://sear.unisq.edu.au/id/eprint/40849 |
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