## issue

Hello all,

I have been wondering for a long time that evalglare outputs a position index below line-of-sight which is not concentric, while the Einhorn’s equation below looks to draw concentric rings because it depends on only Radius.

posindex = 1 + fact * Radius / D

fact and D, which are respectively a slope factor and a distance from an eye to an image plane, should be constant.

so I tried to fix this issue. could someone give me feedback?

## target

in evalglare.c, these 3 lines calculating Radius might cause this issue.

d = 1 / tan(phi);

s = tan(teta) / tan(phi);

r = sqrt(1 / d * 1 / d + s * s / d / d);

## changes

this one line will get a correct Radius.

r = tan(sigma/deg);

then, you won’t need these lines placing a cap on Radius.

/*

if (r > 3) {

fact = 1.2;

r = 3;

}

*/

## effects

the left distribution is the position index by the current evalglare. the right one is by the fixed evalglare. the upper half is the same.

- the lower half of the fixed distribution fits the Iwata’s experiment result better.
- and is concentric as the Einhorn’s equation is.
- the fixed distribution has less deviation between the upper half and the lower half at the eye level.