Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
-
Upload
aist-alliance-for-integrated-spatial-technologies -
Category
Documents
-
view
222 -
download
0
Transcript of Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 1/12
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 2/12
Preacher’s Cave High Definition Survey and 3D
Laser Scanning Project, Eleuthera, Bahamas Introduction:This report presents the results of a High Definition Survey and three-dimensional laser
scanning of the Preacher’s Cave site located in Eleuthera, Bahamas. This project wasundertaken at the direction of Robert Carr, Executive Director of the Archaeological and
Historical Conservancy, who is conducting on-going archaeological investigations at thecave site.
Description of Global Positioning System and Laser Scanning Workflow: Data
was collected during two field days on February 2nd and 3rd, 2006. A site visit was made
on February 1st, which allowed for reconnaissance and choice of scan set-up locations to
maximize the site coverage. A Leica 3000 HDS Scanner was used in the current study to
perform a terrestrial laser scanning survey of Preacher’s Cave. Accuracies of +/-6mm at50m in the x, y, and z dimensions were attained. The scanner captures data in a 360° x
270° field-of-view, and a total of six set-ups were utilized to obtain coverage of the cave
site. The real world coordinates are tied into controls established using GlobalPositioning Systems Real-Time Kinematic Surveying (GPS-RTK) techniques. The point
clouds gathered for the future study would be registered in the Cyclone software version
5.4.
Laser scanning was chosen as a method of recording the Preachers Cave site as it is a
nondestructive technique that offers three-dimensional documentation which includesvisualization and measurement capabilites. The scanned data can be tied to real world
coordinates and used for virtual recording and analysis within a geographic information
system (GIS). Using GIS, pattern analysis, detailed topographic mapping and spatialcorrelations can be analyzed. Previously collected data and location information such as
established benchmarks and coordinates, field specimen and archaeological test areas
and denoted features can be added to the developed GIS and included in the current
analysis, with a spatial database that can be updated as information at the site continues tobe collected. Scanning was an ideal method for the cave setting, as the laser can be used
in all lighting conditions and can even be performed in full darkness. Unlikeconventional line-of-sight total station measurements which can be a time consuming
way of collecting x, y, and z locations, the laser scanner collects millions of
measurements with a high degree of speed and accuracy and can be viewed in three
di i
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 3/12
3) Extensive photographic documentation of the cave site to be utilized to ensure accurate
interpretations of the laser scan data, and to use as photo drapes when appropriate forcontextualizing the scan data.
4) Set-up of the targets to ensure maximum overlap and registration of the scan data with
known locations. Five targets were used in the current study, with each scan view‘seeing’ a minimum of at least three targets in each of the six scan set-ups performed.
5) Post-processing of the data that was recorded by the laser scanner. This includes a
reduction of the dataset to include just the areas identified as being of interest. Duringthe post-processing, a quality control analysis is also performed, which assesses the
accuracy and precision of the recorded data. Finally, the data is exported to a variety of
formats for analysis in other GIS and 3D modeling software. Two dimensional images of the scan data and areas of interest were prepared for inclusion in this preliminary report,
and post-processing continues on the data to analyze areas of investigative interest. As
new findings occur at Preachers Cave, the model can be updated to include spatiallocations, and can also be utilized for a number of visualization, pattern analysis and
measurement needs. The three-dimensional data can also be processed and provided in a
viewable format for interpretive development and understanding for the use and
modification of the landscape through time.
The Scanning Field Procedure: Scanner set-ups consisted of six locations, two
outside of the cave and four set-ups in the interior portion of the cave. These set-ups
utilized five laser targets, which were established inside the cave structure, with eachscan set-up in view of a minimum of three targets (Figure 1). The laser targets are used
in the locational registration of the scan data, and provide spatial control for the scanning
and georeference to a real-world position when combined with the GPS data collected.Target set-up is crucial to the quality of the post-processing by allowing each scan set-up
to be registered in reference to the other scan set-up positions. Sub-meter, differential
GPS was utilized to collect locational data of features on the site including intial scan setup position outside of the cave, previous benchmark locations (Figure 2), and features
such as solution holes located on the ceiling of the cave and accessed from above thecave (Figure 3) and areas of planned improvements to the site (Figure 4). A Trimble
ProXR unit with a TSC1 datalogger was utilized in the current project, utilizing a manual
3D position mode, and taking a minimum of 90 positions on each acquired point location.
Scan set up locations were chosen to work in conjunction with spatial documentation
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 4/12
Figure 1. Target
placement.
Target 2
Target 3
Tar et 5Target 4
Tar et 1
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 5/12
Figure 2.
PreviousBenchmark Locations.
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 6/12
Figure 3. GPSDocumentation of solution
holes on ceiling of cave.
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 7/12
Figure 4. Proposed Improvements.
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 8/12
from archaeological excavation. The developed topographical model of the floor surfacealso portrays and preserves an exact representation using a Cartesian coordinate system
which can be georeferenced to a real world location. The previous mapping of the floorand archaeological features was performed using an arbitrary established coordinatesystem for the site, and was not able to capture the floor detail with the same degree of
accuracy, precision and detail, but is useful in depicting feature locations which will be
used in the current study (Figure 5).
Figure 5. Previous mapping of the cave floor compared to the current study.
Other areas of site documentation included the front ‘pulpit area’ and the front facingrock area with concentration on a section containing several historic period cut nails and
having a feint area of engraving (Figures 6 and 7). Nail pattern analysis from this area
was performed during the preliminary data post-processing and the engraved area was
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 9/12
Figure 6. Nail and engraved area pattern analysis.
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 10/12
Figure 7. Photodrape of front ‘pulpit’ area of cave showing nail and engraving features.
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 11/12
Scan set-ups were also performed in the back and mid-point portions of the cave,including a close range scan on a rock face under a large solution hole which may have
other feint engraved areas. These scan views are still being post-processed and are notavailable for review in this preliminary report. Additionally, a scan from outside the cavewas performed on an area with possible rock art dating to the earlier Taino period. These
scan views will be made available for analysis as post-processing of the data continues.
The scans will also provide three dimensional visualizations, which will be madeavailable in digital format upon completion of the post-processing and can be utilized to
view the cave in a spatially accurate platform and can assist with interpretive
development and archaeological spatial pattern analysis. The overall raw or largely un-
processed data depicts the cave configuration in highly accurate detail, and will be of future use to the on-going heritage management and archaeological research at Preachers
Cave (Figure 8).
8/4/2019 Preacher’s Cave High Definition Survey and 3DLaser Scanning Project, Eleuthera, Bahamas
http://slidepdf.com/reader/full/preachers-cave-high-definition-survey-and-3dlaser-scanning-project-eleuthera 12/12
Figure 8. Raw data collection from interior scan set-up location. Note that vegetation (palm trees) at cave entrance have been
‘digitally removed’ from the scan to allow view into the cave.