Is anyone else on the list going to this?
I'm giving a presentation in the afternoon:
From ASCII files to orthophotos: The processing of high-
resolution aerial survey data using open source GIS software.
High quality maps are an important tool in volcanology. In August 2007 the NERC Airborne
Research and Survey Facility (ARSF) mapped the Nesjavellir region in Iceland's Western Volcanic
Zone. LiDAR, aerial photos and multispectral infrared data were collected with the purpose of
surveying the Nesjahraun, a lava flow that was erupted there approximately 2000 years ago and
which exhibits complex and varied surface textures.
To allow maximum flexibility for the end user,
only low-level processing was carried out by NERC. The remaining processing was carried out
using open source tools, mainly GRASS, GMT, GDAL and gstat to generate higher level products.
The command-line interface of these tools allows tight integration with standard text- and file-
manipulation tools that are built into the GNU/Linux operating system and lends itself easily to the
creation of scripts for the batch processing of multiple files.
The LiDAR data were provided as 6.5 Gb of ASCII text containing information on the location and
intensity of each laser return. A preliminary DEM was prepared by binning the data onto a 10 m
grid in GRASS. For more detailed work, the LiDAR points were interpolated onto a 1 m grid by
kriging using the gstat software in combination with GRASS. This high-resolution DEM was used
to orthorectify the aerial photos and multispectral infrared data by providing both ground control
points and a topographic model. The rectified photos were formatted for printing in GMT to
produce hard-copy maps while false-colour composite images were made by combining different
bands of the multispectral infrared data in GRASS. GRASS was also used to digitise roads and
other features from the orthophotos and to plot measurements made in the field. Conversion of the
format and projection via the GDAL software allows visualisation of much of the data in Google
EarthTM.
The article outlines the GRASS modules and other software tools used to generate high-level
datasets from ARSF data, as a workflow template. It also demonstrates that open source software is
a viable and cost-effective alternative to proprietary software in analysis of GIS data.
Cheers
John
--
Dr John Stevenson
Postdoctoral Research Associate
School of Earth, Atmospheric and Environmental Sciences
Williamson Building (Room 2.42)
University of Manchester
Manchester M13 9PL, UK
tel. +44(0)161 306 6585; fax. +44(0)161 306 9361;
john.stevenson@manchester.ac.uk