Expressing future tense in another way

In English, besides using 'shall' and 'will' to express future tense, we can use 'going to' to achieve the same effect. Let us look at the following pairs of sentences which bear the same meaning each.

1 a) I will go to your house tonight.
b) I am going to your house tonight.

2 a) It will rain soon.
b) It is going to rain soon.

3 a) We shall start a youth camp soon.
b) We are going to start a youth camp soon.