Articles by dylan

Soil Properties Visualized on a 1km Grid

August 31, 2010 | dylan

Fresno Area Urban Areas vs Irrigated LCC: grey regions are current urban areas A couple of maps generated from a 1km gridded soil property database, derived from SSURGO data where available with holes filled with STATSGO data. Soil properties visualize... [Read more...]

GRASS Can Make Pretty Maps

August 23, 2010 | dylan

I have posted a couple examples in the past on the topic of high quality map production from GRASS GIS-- usually via the Generic Mapping Tools. I am not sure why, but I have previously avoided using the traditional cartographic output module that is bu... [Read more...]

PostGIS in Action Book Review

June 8, 2010 | dylan

I was recently asked to review a soon to be published book on PostGIS, a spatial extension to the very popular Postgresql relational database. I was very excited about receiving an early copy of this book, as the authors have provided countless tips, ... [Read more...]

Getting Parent Material Data out of SSURGO

May 27, 2010 | dylan

  Parent material data is stored within the copm and copmgrp tables. The copm table can be linked to the copmgrp table via the 'copmgrpkey' field, and the copmgrp table can be linked to the component table via the 'cokey' field. The following queries illustrate these table relationships, and show one ... [Read more...]

Annotating Lattice Box and Whisker Plots

April 28, 2010 | dylan

bwplot annotation example Sometimes you want to add a little text to box and whisker plots produced by the lattice function bwplot(). Here is one approach. Could be optimized a bit more to reduce manual specification of some elements. Suggestions welcomed. read more
[Read more...]

Converting Alpha-Shapes into SP Objects

April 19, 2010 | dylan

Just read about a new R package called alphahull (paper) that sounds like it might be a good candidate for addressing this request regarding concave hulls. Below are some notes on computing alpha-shapes and alpha-hulls from spatial data and converting the results returned by ashape() and ahull() into SP-class objects. ...
[Read more...]

Estimating Missing Data with aregImpute() {R}

April 19, 2010 | dylan

  Missing Data Soil scientists routinely sample, characterize, and summarize patterns in soil properties in space, with depth, and through time. Invariably, some samples will be lost or sufficient funds required for complete characterization can run out. In these cases the scientist is left with a data table that contains holes (... [Read more...]

Yet Another plyr Example

March 4, 2010 | dylan

another plyr example quantiles (0.05, 0.25, 0.5, 0.75, 0.95) of DSC by temperature bin There are plenty of good examples on how to use functions from the plyr package. Here is one more, demonstrating how to use ddply with a custom function. Note that there are two places where the example function may blow up ...
[Read more...]
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