Localization with AR tags

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We are able to detect 2 AR tags with the corresponding orientation and angles. The thing is that we want to localize the robot within a certain distance at the midpoint of the these 2 tags pointing straight forward. When the robot is exactly facing the tags, it works fine while when the robot comes with an orientation (from the right or the left side of facing the tags) it has problems in positioning exactly at the midpoint of the 2 tags and sometimes it merges in huge error.

Is there any algorithm or a sort from pid controller or any other controller that can solve this problem? In such a way the robot is able to localize at the midpoint of the tags where ever the robot is coming from and once the tags are detected by the camera?

any help?

Thanks in advance