November 19, 2007
GIS Applied to Chaco Canyon, New Mexico
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A significant part of the study is that there is very little evidence of human occupation at Chaco, such as hearths or burial mounds. An example is Chetro Ketl, with 600 rooms, with no ventilation, yet deep, insulated space. Referring to an infrared study, geologist Rich Friedman indicated there wasn’t much cooking activity in the buildings. “If those buildings were lived in continuously, you would expect a trash mound outside twice the size of the building,” he said.
If the immense structures of Chaco Canyon were not lived in, then what was their purpose? Was the largest structure, Pueblo Bonito, built as a symbol to the sun? Sofaer claims that the shapes of the buildings have geometry that appears to be solar and lunar. “There is an internal astronomical geometry in the buildings. Bill and I are doing some GPS on smaller sites.”
Hopi astronomer, surveyor, and geodesist Phillip Tuwaletstiwa with The Solstice Project said that the rising sun rises on the wall of Pueblo Bonito on the two equinox days, and the sun sets on this wall only then. The wall also exactly divides day and night only at this time of year, and the wall divides seasons of year and day from night. Chacoan architects had used these same midpoints of the sun to guide their building.
Why did Chacoans go to such trouble? “Some years it was too dry, too hot, too windy, too cold,” Tuwaletstiwa noted. “If there was a way to transfer the orderly nature of the cosmos down to what seems to be chaos down here, then you would be able to integrate heaven and earth. This would then be viewed in Pueblo culture as a center place.”
New Visions of the Past with GIS
Rich Friedman, GIS Coordinator for the Park Service, City of Farmington, spoke on “Interpreting and Reconstructing the Chacoan Landscape – new visions of the past through the use of GIS.”
He asked the question, “Why use GIS with archaeological sites?” The alignment of Pueblo Bonito with the other structures and with roads fanning out from them is important to solving the Chaco mystery. The Chacoans built well engineered roads throughout 95,000 square miles of the southwest, linking their communities.
The construction phases of Pueblo Bonito, designated as 1 through 5, are illustrated on a map which highlights where cylindrical pottery vessels were found. “We can also put z coordinates on it and put it on terrain. It’s pretty difficult to model through stage 3 of the construction – we don’t know how far the foundations went as they tore down a lot and built again,” Friedman explained.
A laser scan of Pueblo Bonito by Bohannon Huston of Albuquerque depicts construction stage 5 done in virtual GIS, all georeferenced to a point in space. “You can’t experience the entire building until you put it in a virtual model,” Friedman said.
Western Mapping mapped the building Casa Rinconada with geodetic referencing and 3D computer animation. They used texture mapping on the walls, and elevation contours to get exact elevation of any niches. The buildings were re-documented with the help of GPS and cross section analysis was done in 3D.
According to Friedman, the roads are a critical element in the geometry. Using aerial photos from 1934 and LiDAR, you can see the roads illuminated, particularly with a light dusting of snow on the land. A 3D terrain model allows you to rotate the sun’s position to see what the site looks like at certain times of the day and year. “LiDAR can’t be artificially enhanced, it’s raw data,” Friedman pointed out.
Introduction to 3D GIS
In a technical session entitled “Introduction to 3D GIS,” Friedman said that it took 32 hours to render a video image of cinematic quality.
In contrast, 3D GIS is simpler. You can use a photo with a 3D model composited into it, and if you have a 3D program you can render out from a view, and use Photoshop.
Major 3D visualization categories for 3D GIS Data included:
3D Terrain Visualization
- terrain hill shading image data overlay (draping)
- GIS data overlay
-GIS data extrusion
3D object placement (may be GIS data driven)
GIS data driven terrain texturing, 3D object placement, and terrain manipulation
Virtual world/Landscape (may use DEM data)
usually needs to be a USGS DEM which requires that you deal with the data differently.
General 3D animation – non- GIS
3D Terrain Visualization software
- terrain hill shading image data overlay (draping)
- GIS data overlay
may include surface generation analysis capability
GIS Data Extrusion extends to
- include the same basic tool set as 3D terrain visualization software
- extends visualization capabilities to the extrusion of GIS data (points, lines and polygons)
- Typically include surface generation analysis capabilities
3D Object placement--
Example software packages-
- Grass/4D Visualization
- ESRI 3D Analyst
- Virtual GIS – add on to ERDAS Imagine
- Autodesk Map 3D 2007
- Map Maker
GIS Data Driven –
Terrain texturing, 3D object placement, terrain manipulation
Includes same basic tool set as 3D terrain visualization and GIS data extrusion with added capabilities - adding 3D objects and using GIS data to drive object placement environment creation and terrain model.
Has capability to create realistic view of a given area based on GIS data and terrain elevation
Near photorealistic and photorealistic images/animation
- World Construction Set
- Visual Nature Studio (3D nature)
- Genesis II
For photorealistic landscape generation
- Terregen terrain only (free and commercial)
- VistaPro terrains only (inexpensive but not updated in years)
- Vue Esprit
- Bryce ($100)
- World Builder
General 3D modeling and animation software
- designed to provide tools to create a variety of 3D products (illustration, animation, game creation, etc.) SketchUp is good for this.
- Typically requires expert knowledge of GIS and 3D data formats to create semi-compatible data.
- Provides the best output (photorealistic)
- Often used in conjunction with software in previous categories.
- survey data (Point clouds, LiDAR)
- GIS data (visualization analysis)
- Image data (visualization/analysis)
- 3D objects – trees, grass, buildings, etc.
Data used for visualization:
GIS data – lines, points and polygons
- polygons are typically used to simulate 3D structures such as buildings, or specifying areas to designate 3D object populations
- points are typically used for locating individual trees, signs, houses, that are typically depicted by discrete point data in a GIS
- Lines for roads and boundaries and other linear features.
2D or not 2D
Some vector data sets have simple 2D coordinates, some have 3D coordinates (i.e. – “Z shape files”)
For 3D visualization, 2D data sets need a source for base Z coordinates:
-“overlay” data onto an existing surface
Communicates data in a planar format
can add a hill shaded map – physiographic and planar map combined gives good idea of “before and after” picture
In the 3D world, using a digital orthophoto taken of Pueblo Bonito in 2004, you can see how it looks today versus what it looked like in its first construction stage. Additionally, the animation allows you to show things over time, an important capability for this type of historical project.
GPS survey grade data was used to create a DEM, which revealed where breaks in the terrain were, and used to recreate a model of what the buildings might have looked like.
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-- Susan Smith, GISCafe.com Managing Editor.