A note about data scale:
Scale is an important factor in data usage. Certain scale datasets are not suitable for some project, analysis, or modelling purposes. Please be sure you are using the best available data.
1:24000 scale datasets are recommended for projects that are at the county level. 1:24000 data should NOT be used for high accuracy base mapping such as property parcel boundaries.
1:100000 scale datasets are recommended for projects that are at the multi-county or regional level. 1:125000 scale datasets are recommended for projects that are at the regional or state level or larger.
Vector datasets with no defined scale or accuracy should be considered suspect. Make sure you are familiar with your data before using it for projects or analysis. Every effort has been made to supply the user with data documentation. For additional information, see the References section and the Data Source Contact section of this documentation. For more information regarding scale and accuracy, see our webpage at: <http://geoplan.ufl.edu/education.html>
Center for Urban Environmental Solutions: <http://www.cuesfau.org/> <http://www.cuesfau.org/projects/project.asp?ProjectID=107>
FDOT June 2000 Noise Barrier Status Report (Spreadsheet) Contact win.lindeman@dot.state.fl.us for details.
The internal setting of the GeoXT's GPS were set to ensure the highest possible accuracy. The settings utilized are as follows: PDOP: (Position Dilution of Precision) : 6 or less SNR (Signal To Noise Ratio): 4 Elevation Mask: 15% Number of Satellites: 4 or Higher Differential Correction: WAAS
Each noise barrier wall in the region was surveyed to obtain both spatial, attribute and photographic information necessary for the project. Upon arrival to the particular barrier wall, the team would investigate the following conditions before undertaking the survey: Traffic volume & Safety conditions Survey Obstacles GPS Satellite Visibility GPS Availability Upon arrival to the location, traffic volume was determined by the amount of traffic traveling adjacent to the wall of interest. The estimated volume determined whether it was judged safe for a foot survey or required use of a vehicle. Hard hats and florescent safety vests were worn at all times while conducting the surveys.
Numerous barrier walls surveyed had large swaths of vegetation planted next to them. Major types of vegetation included: Sable Palm trees, Sea Grape and various other bushes. These vegetation lines often followed the length of the given wall an ranged on an average from 10-75 feet. Since many of the walls had some type of vegetation, an offset was incorporated into the survey. Generally all surveys were done on an average of 20 feet in front of the wall. Many of the walls not only had a vegetation line in front but also a layer of standing water. This situation occurred in areas where the walls possessed a gully or depression directly in front of the vegetation line. In many situations, the accumulated water actually formed a small linear wetland including typical wetland flora and fauna which included unfortunately high concentrations of biting insects. If these water bodies existed, the offset was increased to account for the additional obstacle so that the survey could continue. Other barriers to the survey included manmade structures such as tollbooths, embankments, bridges and narrow walks. If such obstacles were encountered, the situation was noted in the attribute table and the offset increased as needed.
GPS is a line of sight technology which relies on the ground based receiver the ability to have a clear and unobstructed line of sight to the GPS satellites. noise barrier walls provide a unique problem in that they can obstruct half of the sky depending on how close the survey is conducted to them. Due to this fact, an offset was also needed to obtain the best possible satellite lock. GPS uses a measurement called PDOP (Position Dilution of Precision) to indicate accuracy. To ensure high accuracy GPS positioning, it is recommended that the PDOP value be less than 6. During all wall surveys, PDOP was monitored very closely and any measurement greater than 6 was resurveyed.
Once the Noise Barrier Wall was cleared to survey, the walking team member would activate the Mobile GIS/GPS unit and begin logging the poly-line feature. At the beginning of the logging, an initial starting coordinate would be relayed to the vehicle team member for input into handwriting log. If a walking Survey was done, the survey team member would walk the length of the wall with the vehicle team member following along to provide a look out for traffic. At the halfway point of the survey, the walking team member would again call out the coordinate of the middle of the wall to the vehicle team member. Once the entire length of the wall had been traversed, the walking team member would stop the logging and fill in the custom input form in the ArcPad software. Digital photos were also taken at each survey location.
After each wall was surveyed, the team would back up the data on the GeoXT mobile device and then download the data onto a laptop computer. This procedure was completed at the location incase data was lost and the survey would have to be redone. Once back at the office, all data for that day was downloaded onto the project server to be used by the GIS section.
Acquisition from Individual Districts of Walls in GIS format According to interviews conducted during this project among FDOT personnel, at the time of interviews, District offices were not maintaining an inventory of their noise barriers in GIS. However, in the summer and fall of 2004, two District offices used GPS technology to store their noise abatement walls in GIS.
District Four utilized GPS to store both the point (begin/end points) and line feature classes representing 95 noise abatement walls. District 4 provided the research team with their personal geodatabase. Next, the point and line feature classes were merged and spatially projected into the Statewide Geodatabase. District 4 also created a hyperlink to the photos collected during their GPS work. This hyperlinkis included as part of the Statewide Geodatabase.
District Six utilized GPS technology to capture the begin node and end node for each wall. However, no line feature classes were created. Utilizing the GPS begin and end nodes, the research team digitized the line feature class representing the noise barriers for approximately 84 out of 96 total walls in District 6. A Trimble GeoXT was used to collect the points and linear features depicting the remaining 12 barriers. On Screen (Heads-up) Digitizing
This spatial data collection technique, based on utilizing high quality, rectified aerial photos and other georeferenced GIS layers, was used to primarily to edit the spatial data collected through GPS for relative positional accuracy purposes. The level of accuracy of the derived dataset is taken from the initial accuracy of the digital image along with georeferenced GIS layers.
One of the challenges was to utilize aerial photos in GIS at an acceptable resolution needed to create and edit spatial features for all District offices that have noise abatement walls. The central problem is that most ortho photos in GIS are collected by county governments who collected this raster information at varying scales, different data formats (e.g. MrSID, TIF, JPEG, SDE) and/or captured at different time frames. Based upon these challenges as well as the degree of acquiring these raster features, it was decided to utilize ESRI's ArcWeb Services.
One of ArcWeb Services offered is access to GlobeXplorer's 'Citipix/Digital Ortho' which was used to perform the spatial edits required to verify and/or're-align' the GPS collected data relative to scale of FDOT's GIS base map layers. Citipix is the largest high-resolution aerial imagery dataset available online through ArcWeb Services. Captured at six-inch resolution and in 24-bit color, Citipix is precision geo-referenced and ortho-rectified. It covers over 7,000 cities and towns in over 73 metropolitan areas in the United States, with a total area of over 90,000 square miles.
Because of Citipix high resolution, it provided the optimal back ground layer to digitize, edit, and verify the linear features representing the walls. Using GPS points collected by District 6 which represent the begin and end nodes for each wall along with GlobeXplorer's digital orthophotography, the line feature classes for these walls were digitized. 96 out of the 217 walls within the Statewide Geodatabase were digitized. District 6 accounts for approximately 44% of all noise barriers in the Statewide Geodatabase.