# Question about rtrace

Hi,

I am confused with what rtrace does. Does it just sample one ray at
the input point <xorg yorg zorg> in the direction <xdir ydir zdir> and
calculate the light gained from that direction, or it will sample many
rays through the hemisphere and calculate all the light that reaches
the hemisphere? In the second case, the input direction <xdir ydir

is the normal at point <xorg yorg zorg>.

Yu

Do you want to calculate luminance or illuminance?

CU Lars.

See the man page, '-I' (uppercase 'i') option:

-I Boolean switch to compute irradiance rather than radiance,
with the input origin and direction interpreted instead as
measurement point and orientation.

Regards,
Thomas

···

On 29 Jan 2009, at 07:32, Sheng Yu wrote:

Hi,

I am confused with what rtrace does. Does it just sample one ray at
the input point <xorg yorg zorg> in the direction <xdir ydir zdir> and
calculate the light gained from that direction, or it will sample many
rays through the hemisphere and calculate all the light that reaches
the hemisphere? In the second case, the input direction <xdir ydir
> is the normal at point <xorg yorg zorg>.

Thanks a lot, this is exactly what I want.

···

On Thu, Jan 29, 2009 at 5:36 AM, Thomas Bleicher <[email protected]> wrote:

On 29 Jan 2009, at 07:32, Sheng Yu wrote:

Hi,

I am confused with what rtrace does. Does it just sample one ray at
the input point <xorg yorg zorg> in the direction <xdir ydir zdir> and
calculate the light gained from that direction, or it will sample many
rays through the hemisphere and calculate all the light that reaches
the hemisphere? In the second case, the input direction <xdir ydir
> is the normal at point <xorg yorg zorg>.

See the man page, '-I' (uppercase 'i') option:

-I Boolean switch to compute irradiance rather than radiance,
with the input origin and direction interpreted instead as
measurement point and orientation.

Regards,
Thomas