In Ember, what is the difference between this and this.controller

I'm attempting to build a simple Ember application that collects information from a form. I'm using this tutorial as a guide. In the tutorial it has the following code to grab information from a form:

export default Ember.Component.extend({
  ...
  actions: {
    saveRental1() {
      var params = {
        owner: this.get('owner'),
        city: this.get('city'),
        type: this.get('type'),
        image: this.get('image'),
        bedrooms: this.get('bedrooms'),
      };
      ...
      this.sendAction('saveRental2', params);
    }
  }
});

here is a bit of the relevant form code:

      <div class="form-group">
        <label for="image">Image URL</label>
        
      </div>

      <button >Save</button>
    </form>

In my solution I could not get this to work. this.get('') always showed up as 'undefined' in my code. After a bit of debugging I was able to find a solution, but it meant changing my code from this.get('city') to this.controller.get('city')

Can someone explain what I'm doing wrong or why? Is it 'standard' to use this.controller?