About principle of griddata

Hello there! I am student studying about terrain and DEM. For that, I want to know about interpolation method with matlab. until now, I use griddata(build-in function) for interpolation. And I get some question about that.

1) White line is Delaunay triangles and intersection point of white line is scattered data. And greed circle is the point for interpolation. In this case, are only 3 scattered data near green circle used, or other data also used?

2) I know there are other functions for interpolation(scatteredinterpolant, interp2). Are these functions different? If yes, How are these different? and in the case of image, which is function better?

Thanks for reading my question. please help me.