Suryasiddhanta 3.4.2

3.4.2

śaṅkurapi tatsthānānniṣkāsya iti kevalā dakṣiṇottararekhā sthiteti tātparyam | dakṣiṇottaradiśormadhyasthāne timinā dakṣiṇottararekhāmitena vyāsārdhena dakṣiṇottarasthānābhyāṃ pūrvavat pratyekaṃ vṛttaṃ vidhāya pūrvavat siddhena matsyenetyarthaḥ | pūrvāpaścimā rekhā kāryā | tatra pūrvavindorāsannaṃ rekhāgraṃ pūrvā paścimavindorāsannaṃ rekhāgraṃ paścimeti matsyasambhārjanena kevalā pūrvāpararekhāpi siddhā | atha rekhāsaṃyogasthānāddiksādhanopakramoktaṃ pūrvavṛttamullikhet tadvṛttaparidhau yatra rekhā lagnā tatra digiti tadvṛttamadhyasya dik catuṣṭayaṃ vṛtte siddham | tadvat | yathā dakṣiṇottarābhyāṃ pūrvāparā sādhitā tatprakāreṇetyarthaḥ | evakāro'nyaprakāranirāsārthakaḥ | hi niścayena | vidiśaḥ koṇadiśo diśāṃ pūrvādisiddhadiśāṃ ye madhyagatsyā vyavahitadigdvayāntarotpannā laghavṛttaiḥ saṃsādhyāḥ samyakprakāreṇa sādhyāḥ | rekhāvṛttasaṃyogastvena jñeyāḥ | atopapattiḥ | kṣitijapūrvāparavṛttasaṃyogau pūrvāparavibhāgasthau pūrvāparadiśe tatra pūrvāparavibhāgajñānaṃ sūryodayāstābhyāṃ tatra kṣitije pūrvāparavṛttaṃ kutra lagnamriti jñānaṃ tu viṣuvadvṛttakrāntivṛttasampātasthasūryasyodayāstasthalajñānena viṣuvadvṛttasya pūrvāparakṣitijavṛttasampātayoḥ sambaddhatvāt | athānyasmin dine sūryasyodayāstāvagrāṃśāntareṇa yāmyottare bhavata iti sūryodayāstasthānābhyāmagrāṃśāntareṇottarayāmye pūrvāparasthānaṃ bhavatīti kṣitijasya mahattvāddūratvācca tajjñānena pūrvāparajñānamaśakyamatastatsūtreṇa svābhīṣṭapradeśe tajjñānārthamabhīṣṭasamasthale kṣitijātukāraṃ vṛttaṃ kṛtam |