Saturday, January 18, 2014

LiDAR Works!

A rainy Saturday, with plenty of time to examine LiDAR images. LiDAR is laser scanning of the ground from aircraft.  This has recently been suggested as a tool for mapping stone walls and other features hidden by the forests of New England.  LiDAR images are being incorporated into the topographic maps at Google Maps and Google Earth, but as far as I know, pure LiDAR images are not available.  Luckily, LiDAR data and software for filtering it are available online, and are free!  The LiDAR data files are free for download at    The software is Fusion, which was developed for use by the US Forestry service.  It has plenty of functions for analyzing forest canopy coverage and tree size, and can  pull out the ground points to make a 3-D surface.  Fusion is available at, along with  a tutorial and  data examples.
     Fusion is easy to install, but is not the most user-friendly software to run.  The commands for making the ground point images are entered at DOS level.  There are examples of these commands in the tutorial Exercise 7, Part 2.  I got them to work by copying and pasting into a text file, and rewriting  the file paths as needed. All the images here were generated using the default values given in the tutorial.

Here is a transmitter on top of Neutaconkanut Hill in Johnston, RI.  This view shows all the LiDAR data.  The false color spectrum shifts from blue to red with increased height.  Trees are clearly visible.

Here is the ground surface for the same area, tilted and enlarged.  Houses are clearly visible, as are the two concrete pads for transmitters in the center of the open space.

Here are the cliffs at Snake Den State Park in Johnston, RI. This three-dimensional view will be invaluable in painting reconstructions of sites.
      LiDAR images did show stone walls, but they were faint.  It will probably take some serious tweaking to get the resolution of the images in the Journal of Archaeological Science article.

 This is the same group of walls ending at a cliff that I showed 3/7/2012. The wide walls show up well; the thin connecting wall is barely visible. The diagram below shows the walls.  The cairns merely represent approximate locations of cairns.  Many are quite low and do not show up in the scan.


LiDAR produced a very clear image of the tall, conical cairns at Parker Woodland.  Unfortunately, the corners of four data files met in the cairn field, but most of the cairns were on one corner.  North is at the top of the scan.  I see the trail at upper right. Note the organization of the cairns at the center into two long lines.  There may be a depression between them, which was either a trail or a cart path.

This is definitely a work in progress.  These scans give far more detail than points on a topo map and make it easier to visualize the layout of a site.  I think LiDAR would be very useful for investigating a suspected site before visiting it.

1 comment:

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