I typed that last one too quickly– too many typos, but my wife says I’m not supposed to revise blogs, but move on… . So, for clarity, let’s talk a little more about McNab indices. Field-derived McNab indices are a measure of average angle from the observer to the horizon (mesoscale landform index), or from the observer to another field person a set distance away, … Continue reading Landscape Position and McNab Indices (cont.)
Just a quick teaser post for our forestry/ecology readers out there. I have a methodology developed for calculating McNab indices that directly corresponds with the field technique (unlike, as far as I know, any previous GIS-based techniques– which are probably adequate proxies). What is a McNab index? Well there are two kinds, the minor landforms and mesoscale landforms that are field-measured topographic position or terrain … Continue reading Landscape Position and McNab Indices
I wanted to put together a quick and dirty map of a biological reserve in Ecuador, sort of a laptop exploration of a place quite distant. At first, I thought I’d use Shuttle Radar Topography Misssion data to get the elevation information. Then I discovered the ASTER Global DEM which is 30m resolution for the whole world. Wow. Cool cool data. (I used the Japanese … Continue reading Mapping places unknown– free global datasets and FOSS GIS are a great combo
It finished, yay! A little Friday 5PM exuberance, I’m afraid. See previous post for explanation. Here is the clipped version: Continue reading Clipping Data w/ PostGIS continued
IMCORR is a package distributed by the National Snow and Ice Data Center (did you know we have one of those?), or NSIDC, that performs image cross correlation between two images using a comparison between a moving image chip in each image. It measures the displacement (in pixels) between the objects found in the two images, and writes that out to a text file. It … Continue reading IMCORR– using image correlation to georeference an image
Warning. What follows is somewhat informed, but I’m no geologist. I just play one on wordpress. Understanding the basic underlying geology and associated topography plus site history helps us achieve a basic understanding of a sites ecological potential. At the most basic level, we expect different wildlife and vegetation dynamics in a floodplain vs. a mountain ridge. Classification of digital elevation models can be done … Continue reading Topographic Position Index and Ecological Land Type (warning completely unrefined not quite Geologic dribble– with bad maps 🙂 …)
Yet again, working with that Ohio DEM dataset, I need some reduced resolution versions of the 2.5 foot DEMs. At a grand total of ~600 DEMs for a given county, it was time to batch, this time in Windows Command prompt. The neat thing is the variable substitution in the for-in-do command in the command prompt, where, e.g. for a file variable %f, the file … Continue reading Batch processing resampling of DEMs
Well, I made some mistakes in the last post, not the least of which is I used the wrong flag for creating an attribute field with elevation. What follows is a little more sophisticated. It takes us from a series of DEM tiles from which I want 2-foot and 5-foot contours (using gdal_contour), and then dumps those shapefiles into PostgreSQL using shp2pgsql. First we prep … Continue reading GDAL Contours (cont.)
Just another quick vignette. From the Ohio Statewide Imagery Program (OSIP) there is a 1-meter DEM for all of Ohio. To get contours from this dataset, one approach is to use GDAL tools, i.e. gdal_contours. As I’m working on a Mac today, I used Kyng Chaos pre-compiled Frameworks: http://www.kyngchaos.com/software:frameworks Then I needed to update my path variable in the BASH shell: export PATH=/Library/Frameworks/GDAL.framework/Programs:$PATH Now we … Continue reading GDAL Contours
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