Post on 23-Jan-2017
transcript
LIDAR-derived DTM for archaeology and
landscape history research some recent
experiences with QGIS and GRASS
David Lovelace
david@tilia.org.uk
@boscinet
Using the newly (Sept 2015) released EA LIDAR-
derived DTM. First, merge your 1 km squares
Apply colour styles to the merged
DTM showing height gradations
To display the subtle variations of earthworks
of possible archaeological interest we need
something more sophisticated: GRASS
GRASS has a large number of libraries for most raster
(and vector) operations anyone can think of. Here I’m
using r.slope.aspect which generates new raster using a
variety of surface differential maths operations
Using GDAL from the command line (for Windows useg the msys.exe shell) is
another option – Here are a couple of examples where I’m using the Python library
gdal_calc.py to generate a new DTM by exaggerating the surface differential from
the GRASS r.slope.aspect operation and adding it the original DTM so revealing the
‘ridge and furrow’ and other earthwork features in the Bartonsham meadows:
Raster OS 1:25,000Air photo Bing 2012Result of the GDAL command line processingOverlay of geo-referenced 1st edition 25” to mile c1880 OS map Processed DTM layer and partial transparency of 1880 OS map Overlay of the 1840 tithe map (G. Gwatkins annotated version) Buildings vector layer overlaying the coloured processed DTM 20 cm contours (note the ridge & furrow) – see next slide but one Effect of clipping the DTM raster with vector outline of AOI
Effect of the QGIS3js Plugin
Moorcourt Estate proposed list parkland – water meadow carrier
Control of DTM shadowing using
the Terrain Analysis plugin
EA 2m DTM horizontal resolutionDNP 25cm DTM horizontal resolutionDNP 25 cm DTM differential