Tuesday, 12 February 2013

Review: Kölner R Meeting 6 February 2013

The fourth Cologne R user meeting took place last Wednesday at the Institute of Sociology. Thanks to Bernd Weiß for hosting the event and Revolution Analytics for their sponsorship.

We had two fantastic talks by Klaus Jacobi and M.eik Michalke. Klaus talked about Eliminating cloud pixels in satellite images via chronological interpolation and Meik presented his new roxyPackage package, which makes it even easier to maintain R packages with roxygen2.

Eliminating cloud pixels in satellite images via chronological interpolation

Klaus gave a great case study about his consulting work as a water engineer in Asia, where he used R to analyse the snow melting process in the mountains of Pakistan.

Images of snow melting over time. Klaus Jacobi

About half of the fresh water in some regions of Pakistan is sourced from snow meting during the spring season. The water is captured in dams and as the snow only melts slowly the water supply is much more predictable than the water from the monsoon season, which is the other key source of fresh water during the year.

Satellite images are used to measure the surface covered with snow and to forecast the water supply. Of course snow often coincides with clouds. Hence, many of the pictures don't show a lot at all. Klaus showed us how he used R to develop a script which reads daily raster images of the regions and compares the pictures pixels day by day. He identifies the first and last day without snow cloud cover and interpolates the days in between. This information is than combined with snow depletion curves This data is than used to construct snow depletion curves allowing users to forecast the water supply in spring.

Klaus kindly made his presentation available via his Dropbox folder and also created an animation of the snow melting process, which you can access here.

Creating packages with roxyPackage

Meik is an R user for quite some time and he is also involved in the RKward project. Meik maintains several R packages, so he knows first hand the challenges of keeping all files up-to-date and the documentation in-line with the developments.

Although roxygen2 has made the documentation of R packages much easier, there are still some tasks which need to be done more or less manually, e.g. changing dates and version numbers in DESCRIPTION, Citation and the package Rd-file.

This is the space of roxyPackage as it deals with the package building process and creation of all the necessary files. And here is the clever bit: the packages built are stored in a fully functional local R package repository which can be synced to a web server to share them with others. This includes the generation of browsable HTML pages similar to CRAN, with support for RSS feeds from the ChangeLog. Thus, it has a different purpose than the devtools package maintained by Hadley Wickham.

For more details see the package vignette of roxyPackage. Meik's presentation is also available from this web site.

Next Kölner R meeting, 12 April 2013

The next meeting has been scheduled for 12 April. We already have one presenter: Diego de Castillo will talk about web apps using R and Günter Faes might be ready to present new experiences with the interface development between R and Excel. We are keen to get at least one more talk. Topics of interest to the group are (in no particular order) Rcpp, big data with R, XML parsing with R, time series packages in R, programming with S3/S4, statistical analysis with R, test driven development in R, etc. Please get in touch if you would like to present and share your experience. For more details see also our Meetup page.

4 comments:

  1. Thanks a lot for this good summary. However, to be more precise: rather than comparing the pictures day be day the individual pixels are compared day be day.
    Klaus

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  2. Thanks Klaus. I have updated the post accordingly.

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  3. oops, found another typo. In the phrase "first and last day without snow" please replace "snow" by "cloud cover".
    Greetings from snow-free AND sunny N'Djamena,
    Klaus

    ReplyDelete
  4. Another one: instead "This information is than combined with snow depletion curves" please write "This data is than used to construct snow depletion curves".

    ReplyDelete