Heart of Darkness Vs. Apocalypse Now

It is obvious to those who have viewed both pieces of media that the film "Apocalypse Now" is based off of the book "Heart of Darkness." Both follow basically the same plot, with a team of people going down an unfamiliar and intimidating river in a foreign country. Even the name of the person who is being searched for, Kurtz, is the same in both. However, the similarities, and even the differences of the two are found deeper in their meanings, in the tone and style of the pieces.
In terms of theme, both revolve around a sense of madness. In "Heart of Darkness," all of the characters are ignorant and even fearful of the culture (or as they see it, lack of culture) around them. They see the African villagers as savages, and wonder how any society could possibly that uncivilized. "Apocalypse Now" takes a bit of a different approach to reach the same conclusion. While the soldiers do know a bit more about the society that surrounds them as they traverse the river, the sense of unknowing about the environment and where they are headed is still prevalent. Also, in both pieces the madness is displayed in certain characters. The surfer in "Apocalypse Now" goes crazy after seeing the majority of his comrades die and towards the end is in a state of constant stupor on so many drugs. In "Heart of Darkness," Marlow's obsession with Kurtz also suggests a sense of madness as well.
Savagery and what is truly savage is another common theme between the two. In "Apocalypse Now" the Vietnamese are seen to be the savages, throwing hats with bombs into helicopters and being uncivilized people. However, when the soliders kill the innocent people on the fishing boat, and especially how the last lady is killed, a questioning of what and who is really savage is raised. In "Heart of Darkness," Marlow reflects on the European's abuse of the Africans (such as putting them in chain gangs) and wonders to himself if they are really just masking their barbarism with a cloak of illusional superiority.