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Fort Union-Field Survey

rectified photo
To accomplish the goal of a rapid assessment conditions survey, deterioration,  as well as inherent physical characteristics, such as wall height, wall thickness and number of openings were vital for inclusion and for all of this data to be presented spatially, mapping was necessary. Prior to field work, time was spent creating baseline documentation.
The initial goal for the project was to identify visible changes in the adobe walls, as well as to identify possible causes for those changes, based on comparison with previous NPS data.
Plan Section and Elevation
Working from existing HABS drawings and photographs, a new set of drawings was created. This included an expanded park wide site plan and elevations of the exterior walls of the Mechanics Corral. It also included a comprehensive base plan of the Mechanic’s Corral incorporating all connected spatial data into a single geo-located digital drawing file.
Three Dimensional Modeling?
While three dimensional drawing systems such as Building Information Modeling (BIM) have been making advances for built cultural heritage; plans, sections and elevations still remain the most accessible and common way of conveying architectural ideas as well as providing an easily understood usable format for any long term storage plan. For organizations such as the National Park Service, there is very little clear evidence that BIM data offers advantages. BIM requires specialized training and files saved in formats that are not common to most parks and expensive specialized softwares can be a significant burden to any park as a result of budget limitations, the lack of readily available software training, and the limited duration of many employees at a given park. Three dimensional drawings were considered for the project, but using softwares such as AutoCAD, as well as drawing conventions that were common and easily serviceable (plan section and elevation) were seen as important considerations for the long term storage and usage of these resources. In addition to the obvious advantages of using this common simple solution, the complex shapes of the walls made 3-D modeling far more difficult and would have resulted in a significantly greater investment of time while potentially offering little more in return. In fact the only use of three dimensional drawing was for creating small graphic displays  that were used to help explain how to read the plan view (see image below).
 This allowed for spatial representation of a wide range of displays, both historic as well as conditional, to be created either using AutoCAD or ArcGIS. For the new plan, it was understood that a traditional approach to architectural drawing commonly found in HABS work was not adequate to convey the complex relationship between typical architectural features and the non-traditional aspects of alteration, decay or loss. To understand phenomena such as decay mechanisms for a site like the Mechanics Corral, it is critical that relational information be provided contextually. Plan views fundamentally offer built context by showing the walls of a structure in relation to each other, as well as in relation to cardinal orientation. Scetion Cuts
They do little, however, to express variation in wall heights or less common aspects such as integrity of openings. Using a rigid architectural framework towards plans, sections and elevations to convey three dimensionality, often requires shifting between sheets to fully grasp relationships. 
Rectified Photography
The new plan drawing required a more significant amount of information about the walls. To create the elevation drawings ortho-rectified photographs were used (see image at top). Adobe Photoshop and Agisoft PhotoScan were used to create the rectified photographic elevations. Since drawings and photographs don’t replace, but instead complement each other, the rectified photographs provided additional value beyond their fuction as a foundation on which to build the drawing. While Photoshop is a standard software found in most digital project software packages Photoscan is not, and therefore requires time investment. Photoscan performs photogrammetric processing of digital images generating 3D spatial data by using the relationship between overlapping images. (Along with exportable rectified photomontages, the software can integrate geocoded data when available. During a different phase of the project, this was used to create a 3-D mesh of the second star fort with the aid of a UAV.)

The goal with the newly developed plan was to integrate variations in wall height traditionally offered in elevations, but to do it in a way that it could be viewed contextually in a plan.  In order to provide this more comprehensive picture, additional information placed on the expanded site plan included wall height as expressed as three sectional cuts, each with its own graphic symbology.

  1. The adobe/foundation interface
  2. The traditional height of walls in plan drawings (approximately 4 feet)
  3. Seven feet above foundation which ensured that it exceeded the height of both the tallest windows as well as the tops of all door openings. 

Shape of walls

three levels of plan
Each original wall segment was broken into new "sectors" in order to make each portion of the wall more comparable in mass.