Puente Río Piedras (Historic Bridge #3) — Photogrammetric and field documentation, summary. Public version (English / Español).

Photogrammetric and field documentation of Puente Río Piedras (Historic Bridge #3), Carretera Central, barrios El Cinco / Hato Rey, San Juan, Puerto Rico. Version 2.0 covers two field dates: the aerial survey of 17 August 2026 and the field campaign of 6 September 2026. The three-dimensional model derives from a 52-image continuous sequence processed in OpenDroneMap 3.5.6. The base run achieved a ground sampling distance of 0.2 cm per pixel, a reprojection error of 1.08 pixels, a total GPS RMS error of 0.574 m, and relative horizontal precision reported between 0.074 m and 0.161 m across two processing runs of the same image set. That discrepancy is recorded and is not resolved; any measurement taken on the model is to be reported against the more conservative figure. Absolute horizontal precision is 0.764 m (CE90), consistent with GPS georeferencing without ground control points. The report sets out the structure's National Register of Historic Places listing (reference 95000832, listed 19 July 1995, Historic Bridges of Puerto Rico MPS), its Puerto Rico Register designation of 3 February 2000, its status as a contributing property of the Distrito Histórico del Acueducto de San Juan, the verbatim transcription of the granite parapet plaque, unresolved discrepancies in the record, capture and airspace-authorization detail for both campaigns, camera calibration, precision limits, observed surface conditions, and twelve figures. New in version 2.0: the campaign of 6 September 2026, operated beneath the deck within the central arch; the first direct tape measurements taken in this series; the third opening documented photographically for the first time; a third independent dataset confirming the camera's focal-length convergence; and two open discrepancies — the granite plaque height and the EXIF coordinate under the deck. The September captures are unprocessed and no model derives from them. This record contains the English and Spanish public versions of the same document. It is an open-access spatial and archival record. It is not a structural study, a condition appraisal or a topographic survey.