Make an isochrone from a surfaceSource:
Make a raster image (picture) of travel time using the surface features in OTP 1.x
OTP connection object produced by otp_connect()
A suface list from otp_make_surface()
THis function requires the analysis and pointset features to be enabled during `otp_setup()`. Thus it will only work with OTP 1.x. For more detail see the analyst vignette.