Manasara 6.53

6.53

garbhasūtrasya karṇaiśca dvidviśaṅku nikhānayet
caturdikṣu catuḥśaṅkuṃ janmaniṣkramaṇārthakam

at the corners of the center-cord (garbhasūtra), he should drive two gnomons each; / four gnomons in the four cardinal directions for the sake of the entrance-exit layout;