If we take "Pornography" first, this is quite recent, originating from the Greek word "pornographos", or "writing about prostitutes". Very specific ! Today, it is defined as "intended to stimulate erotic feelings"
Erotic, Erotica, Erotism, Eroticism, etc., all pertain to the root word "Eros", Son and lover of Aphrodite (or Venus to the Romans), and all pertain to "sexual desire or excitement".
As such, it is clear in modern day terms, that pornography and erotica are closely linked. Pornography can be erotic just as erotica can be pornographic. Equally, it cannot automatically be taken as given. Much is in the eye of the beholder and what does or does not stimulate the viewer. Let us also not forget, that what stimulates man does not necessarily stimulate woman, and vice-versa.
For me at least, modern day pornography is largely just sexual, often commercially sexual to the extreme, whereas erotica is (or at least should be) primarily sensual, sensuality being the primary stimulant. Voila, there you have my two-penneth worth !