Saturday, February 1, 2014

An Old Farm in LIDAR

Deep in the woods in Tiverton, RI is an old farm. A well-made wall marks the boundary.

Beyond are some evocative structures.  Loose stone rows are visible under the leaves.

I have heard that loose stone rows were  created when a farmer threw rocks against a wooden fence while plowing the field.
     There are more  walls and large rock piles further on.  These have a variety of stone sizes, with the largest at the bottom, and look like someone tossed the smaller stones on top.

These don't have the very neat, symmetrical appearance of cairns at other sites, and may have been constructed by a farmer clearing fields or storing stones for use in the walls.

Here's the old farmhouse  foundation, and  the same place in LIDAR. I increased the image contrast to show more details.

 The farm is at lower left.  Walls are visible, with the farmhouse foundation inside the larger enclosure.  Directly south is a smaller enclosure containing the large rock piles shown above.  An old farm road runs across the site directly to the north of the farm. There is also an old path that runs north to the farm road.  LIDAR shows paths even if they are not worn very deep into the ground.  Maybe the denser soil  in a path or road is detected.

     All the LIDAR images I have shown were created using the Fusion LDV, hence the USDA Forest Service logo across the top. In my last post, I mentioned that Fusion can convert surface files to JPEG or TIF images.  The TIF ground surface images are flat and hard to read. JPEGs created with the Intensity Image command are grainy, but at least have much more detail and are useful as reference images.

This is the larger area containing the farm.  Houses and streets are visible to the right.  A brooks runs south from  the dark swamp at top center in the image.  Other swamps and ponds are visible as dark areas.  The yellow and red lines are topo lines created using the ground surface layer data and colored  for contrast.  The brook appears white in the center of the image because the LDV is sampling that area.
   Fusion is easy to use and allows quick sampling and visualization of small areas, but does not support export of high-quality images.  It was designed to produce ASCII and DTM files for export to ArcGIS, a mapping software package.  Unfortunately, ArcGIS is quite expensive, but the open-source Grass GIS is also designed to work with these file types, GPS input, and raw LIDAR data.  I am trying it out.  This may take a while...

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