Orthorectified Wall Imaging

Purpose

In preparation for the graphic conditions assessment planned for the Pecos South Pueblo, orthorectified photographs were produced of all extant wall elevations and tops. The orthorectified images serve multiple purposes: they document the current condition of standing features, provide base layers for graphic condition assessments and recording of potential treatments and rebuilds, serve as a reference for future condition assessments, and facilitate long-term monitoring of deterioration patterns. During the process of creating these images, innovative techniques were utilized, enhancing the quality of the imaging for further application.

Solution to On-Site Photography Challenges

Outdoor lighting

Ideally, photos would be taken on overcast days, but limited field time required efficiency without compromising quality. The bracketing technique, capturing multiple exposures of the same view, was used to balance shadows and overexposure. Overexposed shots revealed shadowed details, underexposed ones captured sunlit areas, and balanced exposures provided reference points for software alignment. While effective, this approach significantly increased the number of photos needed.

Irregular rubble masonry units

The irregular units create many creases and negative spaces on the wall elevations. This complex geometry sometimes required extra photographs to be taken at multiple angles to capture their configurations completely. While software requires at least 80% overlap for successful alignment to create a point cloud, exceeding this minimum always improves the success rate, especially when irregular and complex wall configurations pose uncertainties about photographic strategies.

Photograph Processing

After fieldwork, the photographs were processed using RealityCapture, an open-source software developed by US gaming company Epic Games. RealityCapture was experimented with and used by the CAC for orthorectification as a potential alternative to Agisoft Metashape due to several advantages:

High-quality point cloud and high-resolution orthorectified images
Reduced processing times compared to Agisoft Metashape. A typical image set of 30 photographs required less than half the time to process in RealityCapture.
While Agisoft Metashape requires an expensive license to access professional features, including exporting orthorectified images, RealityCapture is developed by a US company and available for free for nonprofit use. The software therefore eliminates cyber safety concerns and presents improved economic value for work at National Parks.

Render in Agisoft or Reality Capture

Clean up in Photoshop

Layout in Final Conditions Sheet

Despite its advantages, RealityCapture is less effective in aligning images with complex geometries than Agisoft Metashape. To address these challenges, manual marker placement and supplemental processing in other software such as Adobe Photoshop were employed (as seen above). The integration of these tools enabled the recovery of missing data and enhanced overall image quality. Processed orthorectified images underwent further adjustments to optimize brightness, contrast, and color balance. Adobe Photoshop played a critical role in fine-tuning image quality, especially for cases where the SfM software could not fully address visual inconsistencies. These images were formatted into 11” x 17” templates for practical field use. The outcomes of this work include both a set of orthorectified images of the South Pueblo and findings and recommendations regarding photogrammetric work specifically addressing architectural features at Pecos, as well as a set of historic preservation technical guides detailing workflows to implement these methodologies.

A total of 268 wall elevations and wall tops were documented, corresponding to the 109 identified wall segments. Of these, 249 elevations (over 90%) were successfully processed into orthorectified images, with approximately 13% of the 90% requiring additional enhancements in Photoshop. The remaining elevations failed to align due to insufficient photographic overlap or inadequate visual coverage, underscoring the need for improved field photography protocols.

Orthorectification results by success rate in RealityCapture

The experience highlighted the importance of developing tailored workflows that leverage the strengths of multiple software tools. For example, while RealityCapture excelled in speed, Metashape provided relatively better alignment capabilities, and Photoshop enabled detailed manual editing. This combination ensured high-quality results and demonstrated the value of flexibility in documentation strategies. Further quality improvements were achieved through color correction and resolution enhancement, resulting in images that are both visually clear and highly accurate.

Page updated

Google Sites

Report abuse