Articles by dylan

SoilWeb iPhone App: Beta-Testers?

February 23, 2010 | dylan

iPhone App Screenshot rev 0.2 - icon iphone App Screenshot rev 0.2 - in Fresno   More Updates: The application is now available on the Apple iTunes Store. Preliminary documentaion here. read more
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Numerical Integration/Differentiation in R: FTIR Spectra

February 23, 2010 | dylan

  Stumbled upon an excellent example of how to perform numerical integration in R. Below is an example of piece-wise linear and spline fits to FTIR data, and the resulting computed area under the curve. With a high density of points, it seems like the linear approximation is most efficient and ...
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Visual Interpretation of Principal Coordinates (of) Neighbor Matrices (PCNM)

February 21, 2010 | dylan

Principal Coordinates (of) Neighbor Matrices (PCNM) is an interesting algorithm, developed by P. Borcard and P. Legendre at the University of Montreal, for the multi-scale analysis of spatial structure. This algorithm is typically applied to a distance matrix, computed from the coordinates where some environmental data were collected. The resulting "... [Read more...]

Two New Soils-Related KMZ Demos

February 10, 2010 | dylan

LCC KMZ Soil Texture KMZ   Forgot to post these KMZ files: 1-km scale, aggregate LCC and soil texture data, derived from SSURGO. These are part of a series of KMZ / raster datasets that will be published soon. See attached files at the bottom of the page. Enjoy! read more
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Updates to SoilWeb

January 17, 2010 | dylan

Soil Profiles in Color Added color support to the mini-profiles used in graphical map unit summaries, the Google Earth interface, and iPhone application. SSURGO doesn't contain soil color data, so colors (in Munsell notation) were extracted from the OSD database, and converted into RGB triplets. Using horizon information from the ...
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Interesting use of levelplot() for time series data

January 16, 2010 | dylan

levelplot example: soil temperature (left) and moisture (right) Several recent articles appeared on the R-bloggers feed aggregator that demonstrated an interesting visualization of time series data using color. This style of visualization was readily adapted for the time series data I regularly collect (soil moisture and temperature), and quickly implemented ...
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Estimated Net Worth of SoilWeb- Our Online Soil Survey

December 28, 2009 | dylan

According to the excellent source code evaluation tool, SLOCCount, our online soil survey (SoilWeb) code is worth about $268,543 and would require about 2 years of development time to re-create from scratch with a single developer working full-time. This is a fairly close estimate, as I have been working (part-time) on this ... [Read more...]

Un-Wrapping a Sphere with R

December 8, 2009 | dylan

  Premise I was recently asked to print out a fabric pattern that could be used to cover a sphere, about the size of a ping pong ball, for the purposes of re-creating a favorite cat toy (quite important). Thinking this over, I realized that this was basically a map projection ... [Read more...]

New R-Forge Site for Quantitative Pedology

November 8, 2009 | dylan

Just back from the annual meetings, and it looks like there is a significant interest in collaborative R coding of soils-related algorithms and visualization. A new R-forge site has been created to host Algorithms for Quantitative Pedology. Public release of the 'soil' package should be ready in a couple weeks. ... [Read more...]

Aggregating SSURGO Data in R

September 10, 2009 | dylan

  Premise SSURGO is a digital, high-resolution (1:24,000), soil survey database produced by the USDA-NRCS. It is one of the largest and most complete spatial databases in the world; and is available for nearly the entire USA at no cost. These data are distributed as a combination of geographic and text data, ... [Read more...]

Potential Loss of Arable Land in the Central San Joaquin Valley, CA

August 17, 2009 | dylan

Rapid urban and sub-urban expansion in the San Joaquin Valley have resulted in the loss of millions of acres of prime farmland in the last 100 years. Approximately 11% of class 1 (irrigated) land and 7% of class 2 land have already been paved over in the Fresno-Madera region (first image below). Recent projections in ... [Read more...]

Using R to Create Misc. Patterns [smocking]

July 4, 2009 | dylan

Pattern Chunk   Premise My wife asked me to come up with some graph paper for creating smocking patterns. After a couple of minutes playing around with R-base graphics functions, it occurred to me that several functions in the sp package would simplify grid-based operations. Some example functions, along with a ... [Read more...]

Summarizing Grouped Data in R

July 3, 2009 | dylan

A colleague of mine recently asked about computing basic summary statistics from grouped data in R. These are a couple examples that I suggested. Additional documentation for the plyr package can be found here. read more [Read more...]

Accessing Soil Survey Data via Web-Services

May 28, 2009 | dylan

Soil Survey Data   Online Querying of NRCS Soil Survey Data Sometimes you are only interested in soils data for a single map unit, component, or horizon. In these cases downloading the entire survey from Soil Data Mart is not worth the effort. An online query mechanism would suffice. The NRCS ... [Read more...]

Making Sense of Large Piles of Soils Information: Soil Taxonomy

May 27, 2009 | dylan

Western Fresno Soil Hierarchy: partial view of the hierarchy within the US Soil Taxonomic system   Soil Data Field and lab characterization of soil profile data result in the accumulation of a massive, multivariate and three-dimensional data set. Classification is one approach to making sense of a large collection of this ... [Read more...]

Simple Approach to Converting GRASS DB-backends

May 23, 2009 | dylan

  Premise: The current default database back-end used by the GRASS vector model is DBF (as of GRASS 6.5), however this is probably going to be changed (to SQLite) in GRASS 7. The DBF back-end works OK, however it tends to be very sensitive (i.e. breaks) when reserved words occur in column ... [Read more...]
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