OK, if you are really lost, try using different vision modes for navigation.
the blue one is the Thermal vision, you should be familiar with it from the movies. it draws the heat of the human bodies with a scale of bright colors. the brightest the colors, the hottest the source. human bodies disappear after a while, when their heat dissipate, but you can still pick up the heads that you gibed with your speargun.
the red one is electrovision and will help you see aliens and metallic equipment(marine weaponry F.E.). it works by detecting the magnetic field of objects with high electric current, like the alien blood and other machinery.
the last vision mode is the green/grey one, and is called Pred-Tech. it detects the waves of energy emited by Predator technology. It will be very Useful when you're looking for weapons, ammo, and other predators. you can also use pred-tech to navigate the levels, since its the brightest and gives you more contrast between the trees and the rocks around it.
(i could go on all day, I'm really good at explaining things
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