SURFL "elevation" and "azimuth" definition

Hello,

I need to extract the reflectance data from the "surfl" function but I am having trouble in understanding the "azimuth" and "elevation" parameters of this function. The function uses a default value which is defined as "The default s is 45° counterclockwise from the current view direction". What is this "current view direction" because I don't set any "view" fuction for the plot?

However, after playing around with multiple figures and AZ and EL parameters, I think that the AZ=0 deg means in the south direction of the data and EL=0 is the horizon. What is the unit of the EL parameter? Is it in degrees? I've tried using EL=90 and it seemed like it was from nadir but I'm still not sure.

Please let me know if I got this right.

Thank you.

Answer 1

[Chidvi Modala]

You may refer to the below link for a clear understanding on viewpoints

Viewpoint with azimuth and elevation

[Fadhli Atarita]

Hi,

Thank you for your reply. That is a very useful documentation.

What I'm still confused of is that a 3D plot has a default viewpoint of azimuth = -37.5° and elevation = 30°. and in the documentation of surfl, it is stated that s= "Direction from the surface to the light source, specified as a two- or three-element vector. The vector has the form [sx sy sz] or [azimuth elevation]. The default direction is 45° counterclockwise from the current view direction."

Does that mean 45° from the -37.5° viewpoint (which is basically 7.5°) or literally 45° regardless of the default 3D viewpoint ? and there is no stated default elevation, can i assume that it is 0°?

Fadhli

Answer 2

[Chidvi Modala]

surfl doesn't have a default viewpoint, the view belongs to the axes. Consider:

view(3)
[az,el] = view
az =
 -37.5000
el =
   30

view([10,20])
[az,el] = view
az =
   10
el =
   20

If the s parameter is not specified it is calculated as 45 degrees counterclockwise from the current view direction.

The light is placed at the coordinate [Sx,Sy,Sz] where:

Sx = cos(az)*sin(45)+sin(az)*cos(el)*cos(45)

Sy = sin(45)*sin(az)-cos(az)*cos(el)*cos(45);

Sz = sin(45)*sin(el);

If the s parameter is specified as a two element vector: Saz, Sel, the light is placed at:

Sx = sin(Saz)*cos(Sel)

Sy = -cos(Saz)*cos(Sel)

Sz = sin(Sel)

If the s parameter is specified as a three element vector, we use those elements to define Sx, Sy, Sz.

If you'd like to learn more about where the light is placed, feel free to experiment with:

h=surfl(rand(5),rand(5),rand(5), [0 0], 'light');
h(2).Position

You can also experiment with:

edit surfl.m

[Fadhli Atarita]

Thank you!