I have a a polygon shapefile of different regions, and a raster grid of precip data. I want to take the polygon and add up all the raster precip data in each zone. I could use zonal statistics to do this, however the tool does not split pixels exactly where the polygon edge cuts through the a pixel, it instead takes either the whole pixel value or not at all. I could convert the raster data to polygons, but I was wondering if there was a way to do this without going to polygons.
You can't easily get values from a fraction of a pixel, in fact, you probably don't want to get into this at all. You could always resample your raster to a higher resolution (e.g. from 50cm to 10cm) in order to better follow the polygon boundary. This method will still allow you to run zonal statistics.