I am analyzing some animal tracking data and I have a problem that I am stumped by. Imagine that we have a single animal track (created from satellite data received about once per hour), and that it wanders for many kilometers. I would like to overlay a grid on the track (cell size about 500 m x 500m) and record a direction vector for every cell in the grid, which represents the direction that the animal was traveling when it passed through that cell. I tried using v.to.rast with use=dir, which should create a directional vector in every raster cell that the track passes through, but it seems that the command does not respect the order of the track. In other words, it seems that it was just as likely to classify a particular segment as having a direction of NE as it was to classify the same segment as SW (180 degrees opposite), and I couldn’t see any consistency to how the directions were chosen, although I may have missed something. There are a few other challenges, including that sometimes the animal re-crossed its own track so that a grid cell may contain more than one track. In those cases I would want to sum the vectors (with regular vector addition). I want to do a few other things as well, including finding the center of each grid cell and computing a direction vector that is orthogonal to some linear landscape feature—I only mention this in case rasters are not the right approach. I am new to GRASS and a bit overwhelmed, and I would be very grateful for any suggestions that would get me started in the right general direction.
Thanks!