This visualization displays the trajectory of points with varying phi and theta angles, mapped to x and y coordinates, with a density contour overlay that animates in progressively. The color of the contours reflects the selected slowness value (p, s, or t) chosen via a dropdown menu. The visualization uses D3.js libraries including `contourDensity`, `geoPath`, `scaleLog`, and `transition` to render the SVG paths and smoothly animate their appearance. The data comes from a precomputed `data_xy` array, and the square plotting area is bounded between -1.5 and 1.5 on both axes.