I need to create a map of pressure shades using a point data set having each point its value of pressure. So I need to give a color to each point based on its pressure value. But after that I need the spaces between points to be fill with the interpolation color between every four points.
Unless, you really want to generate a different map with every request (and why would you want to do that?) then this is a bad idea as edge effects and slight differences in bounding boxes will lead to strange effects. For example, here is a tiled heat map of the US population.
What you really, want to do is use QGis or some other desktop system to make a raster using any of the many interpolation methods and then add the resulting fixed raster to GeoServer.