This week’s meeting focused on talks given by Lisa and Jeeyoung.

Lisa talked first, discussing her latest project using **Data-Driven Documents (d3)**. The dataset of choice was the *Iris* dataset, that which any R enthusiast will be familiar with. It contains five variables: *Sepal.Length, Sepal.Width, Petal.Length, Petal.Width, *and *Species*.

For those unfamiliar with d3.js, it is a visualization library that provides functionality to bind data to objects. The advantages of using d3.js is that it is extremely fast and flexible.

Here is a simple example of selecting a circle and updating it with new coordinates and size :

var circle = svg.selectAll(“circle”)

.attr(“cy”, 90)

.attr(“cx”, 30)

.attr(“r”, 40);

But what if we want to make it more interesting. Consider a data set of size two (i.e [20, 35]). D3.js makes it easy to add a new circle and visualize the data in such a way that the size and x-coordinate of each circle reflects each data point.

var circle = svg.selectAll(“circle”)

.data([20, 35])

.enter().append(“circle”)

.attr(“cy”, 90)

.attr(“cx”, function(d) {return d;})

.attr(“r”, function(d) {return d;});

Lisa’s project explored multiple visualization strategies including an easy-to-use interface to change the axis of a scatter plot.

Jeeyoung discussed **edge detection and line detection**. In edge detection, a user applies an algorithm (that uses a threshold on the directional derivatives) to produce an image with the original’s edges. One of the more common edge detection algorithms is *Canny edge detection *(see below: source Wikipedia).

From there, you can apply line detection. It is easier to do this by mapping each point along the edges to a line in the parameter space (slope-intercept coordinate plane) and looking for intersections. While the exact details will not be mentioned, the transformation to be used is the *Hough Transformation*.

Note you can implement both using Matlab commands : *edge(.)* and *hough(.)*

As usual come join us in the Stats Club Office every Monday at 4:30pm!