Development of a GPS-Based Sign Inventory Tool for Iowa’s Statewide Management System, May 2011

This report is on state-of-the-art research efforts specific to infrastructure inventory/data collection with sign inventory as a case study. The development of an agency-wide sign inventory is based on feature inventory and location information. Specific to location, a quick and simple location acquisition tool is critical to tying assets to an accurate location-referencing system. This research effort provides a contrast between legacy referencing systems (route and milepost) and global positioning system- (GPS-) based techniques (latitude and longitude) integrated into a geographic information system (GIS) database. A summary comparison of field accuracies using a variety of consumer grade devices is also provided. This research, and the data collection tools developed, are critical in supporting the Iowa Department of Transportation (DOT) Statewide Sign Management System development effort. For the last two years, a Task Force has embarked on a comprehensive effort to develop a sign management system to improve sign quality, as well as to manage all aspects of signage, from request, ordering, fabricating, installing, maintaining, and ultimately removing, and to provide the ability to budget for these key assets on a statewide basis. This effort supported the development of a sign inventory tool and is the beginning of the development of a sign management system to support the Iowa DOT efforts in the consistent, cost effective, and objective decision making process when it comes to signs and their maintenance.

Use of GPS for Photogrammetry, HR-342, 1993

Five test flights were conducted to study the use of Global Positioning System (GPS) in Photogrammetry, three in Iowa, one each in California and Texas. These tests show that GPS can be used to establish ground control by the static method and to determine camera location by the kinematic method. In block triangulation, six GPS controls are required and additional elevation control along the centerline is also required in strip triangulation. The camera location determined by aerial triangulation depends on the scale of the photography. The 1:3000 scale photography showed that the absolute accuracy of the camera location by GPS is better than five centimeters. The 1:40000 scale photography showed that the relative accuracy of the camera location by GPS is about one millimeter. In a strip triangulation elevation control is required in addition to the camera location by GPS. However, for block triangulation camera location by GPS is sufficient. Pre-targeting of pass and tie points gives the best results in both block and strip triangulation. In normal mapping for earth work computations the use of 1:6000 scale photography with GPS control instead of 1:3000 scale is recommended. It is recommended that research be done in the use of GPS for navigation in aerial photographic missions. It is highly recommended that research be done in the use of GPS to determine tip and tilt of the aerial camera, that is required in stereoplotting.

Soft Photogrammetry for Highway Engineering, HR-387, 1998

The SoftPlotter, a soft photogrammetric software and Silicon Graphics workstation, was used to evaluate the accuracy of soft photogrammetry and identify applications of this technology to highway engineering. A comparative study showed that SoftPlotter compares well with other software such as Socket and Integraph. The PC software TNTMips is inexpensive but needs further development to be comparable to SoftPlotter. The Campus Project showed that soft photogrammetry is accurate for traditional photogrammetric applications. It is also accurate for producing orthophoto and base maps for Geographic Information Systems (GISs). The Highway Project showed that soft photogrammetry is accurate for highway engineering and that the technical staff at the Iowa Department of Transportation (IA DOT) can be easily trained in this new technology. The research demonstrated that soft photogrammetry can be used with low-flight helicopter photography for large-scale mapping in highway engineering. The researchers recommend that research be conducted to test the use of digital cameras instead of the traditional aerial cameras in helicopter photography. Research that examines the use of soft photogrammetry with video logging imagery for inventory and GIS studies in highway maintenance is also recommended. Research is also warranted into the integration of soft photogrammetry with virtual reality, which can be used in three-dimensional designing and visualization of highways and subdivisions in real time. The IA DOT owns one analytical plotter and two analogue plotters. The analytical plotter is used for aerial triangulation, and the analogue plotters are used for plotting. However, neither is capable of producing orthophotos. Therefore, the researchers recommend that the IA DOT purchase soft photogrammetric workstations for orthophoto production, and if and when required, use it for aerial triangulation and plotting. In the future, the analogue plotters may become obsolete. At that time, the researchers recommend that the analogue plotters be phased out and replaced by soft photogrammetric workstations.

Optimization of Snow Drifting Mitigation and Control Methods for Iowa Conditions Part II, TR-626, 2015

Blowing and drifting of snow is a major concern for transportation efficiency and road safety in regions where their development is common. One common way to mitigate snow drift on roadways is to install plastic snow fences. Correct design of snow fences is critical for road safety and maintaining the roads open during winter in the US Midwest and other states affected by large snow events during the winter season and to maintain costs related to accumulation of snow on the roads and repair of roads to minimum levels. Of critical importance for road safety is the protection against snow drifting in regions with narrow rights of way, where standard fences cannot be deployed at the recommended distance from the road. Designing snow fences requires sound engineering judgment and a thorough evaluation of the potential for snow blowing and drifting at the construction site. The evaluation includes site-specific design parameters typically obtained with semi-empirical relations characterizing the local transport conditions. Among the critical parameters involved in fence design and assessment of their post-construction efficiency is the quantification of the snow accumulation at fence sites. The present study proposes a joint experimental and numerical approach to monitor snow deposits around snow fences, quantitatively estimate snow deposits in the field, asses the efficiency and improve the design of snow fences. Snow deposit profiles were mapped using GPS based real-time kinematic surveys (RTK) conducted at the monitored field site during and after snow storms. The monitored site allowed testing different snow fence designs under close to identical conditions over four winter seasons. The study also discusses the detailed monitoring system and analysis of weather forecast and meteorological conditions at the monitored sites. A main goal of the present study was to assess the performance of lightweight plastic snow fences with a lower porosity than the typical 50% porosity used in standard designs of such fences. The field data collected during the first winter was used to identify the best design for snow fences with a porosity of 50%. Flow fields obtained from numerical simulations showed that the fence design that worked the best during the first winter induced the formation of an elongated area of small velocity magnitude close to the ground. This information was used to identify other candidates for optimum design of fences with a lower porosity. Two of the designs with a fence porosity of 30% that were found to perform well based on results of numerical simulations were tested in the field during the second winter along with the best performing design for fences with a porosity of 50%. Field data showed that the length of the snow deposit away from the fence was reduced by about 30% for the two proposed lower-porosity (30%) fence designs compared to the best design identified for fences with a porosity of 50%. Moreover, one of the lower-porosity designs tested in the field showed no significant snow deposition within the bottom gap region beneath the fence. Thus, a major outcome of this study is to recommend using plastic snow fences with a porosity of 30%. It is expected that this lower-porosity design will continue to work well for even more severe snow events or for successive snow events occurring during the same winter. The approach advocated in the present study allowed making general recommendations for optimizing the design of lower-porosity plastic snow fences. This approach can be extended to improve the design of other types of snow fences. Some preliminary work for living snow fences is also discussed. Another major contribution of this study is to propose, develop protocols and test a novel technique based on close range photogrammetry (CRP) to quantify the snow deposits trapped snow fences. As image data can be acquired continuously, the time evolution of the volume of snow retained by a snow fence during a storm or during a whole winter season can, in principle, be obtained. Moreover, CRP is a non-intrusive method that eliminates the need to perform man-made measurements during the storms, which are difficult and sometimes dangerous to perform. Presently, there is lots of empiricism in the design of snow fences due to lack of data on fence storage capacity on how snow deposits change with the fence design and snow storm characteristics and in the estimation of the main parameters used by the state DOTs to design snow fences at a given site. The availability of such information from CRP measurements should provide critical data for the evaluation of the performance of a certain snow fence design that is tested by the IDOT. As part of the present study, the novel CRP method is tested at several sites. The present study also discusses some attempts and preliminary work to determine the snow relocation coefficient which is one of the main variables that has to be estimated by IDOT engineers when using the standard snow fence design software (Snow Drift Profiler, Tabler, 2006). Our analysis showed that standard empirical formulas did not produce reasonable values when applied at the Iowa test sites monitored as part of the present study and that simple methods to estimate this variable are not reliable. The present study makes recommendations for the development of a new methodology based on Large Scale Particle Image Velocimetry that can directly measure the snow drift fluxes and the amount of snow relocated by the fence.

Airborne GPS Final Report, HR-359, 1995

The objective of this project was to use a Global Positioning System (GPS) to determine the aerial camera location and orientation that best facilitated mapping done from aerial photographs without any ground control. Four test flights were conducted. The first test flight was performed in June 1993 at St. Louis, with the objective of testing the multiantenna concept using two antenna on the aircraft. The second test in August 1993 was conducted over the Iowa State University (ISU) campus at Ames. This flight evaluated the use of GPS for pinpoint navigation. The third test flight over St. Louis was flown in October 1993, with four antenna on aircraft; its objective was to evaluate the 3DF GPS receiver and the antenna locations. On the basis of the results of these three tests, a final test flight over the Mustang Project area in Ames and the ISU campus was conducted in June 1994. Analysis of these data showed that airborne GPS can be used (1) in pinpoint navigation with an accuracy of 25 m or better, (2) to determine the location of the camera nodal point with an accuracy of 10 cm or better, and (3) to determine the orientation angles of the camera with an accuracy of 0.0001 radians or better. In addition, the exterior orientation elements determined by airborne GPS can be used to rectify aerial photos, to produce orthophotos, and in direct stereo plotting. Further research is recommended in these areas to maximize the use of airborne GPS. The report is organized in the following chapters: (1) Introduction; (2) Photogrammetry and Kinematic GPS; (3) Analysis of First Test; (4) Analysis of Second Test; (5) Analysis of Third Test; (6) Analysis of Final Test; (7) Applications of Airborne GPS; and (8) Conclusion and Recommendation.

GPS to LRM: Integration of Spatial Point Features with Linear Referencing Methods, 2001

Global positioning systems (GPS) offer a cost-effective and efficient method to input and update transportation data. The spatial location of objects provided by GPS is easily integrated into geographic information systems (GIS). The storage, manipulation, and analysis of spatial data are also relatively simple in a GIS. However, many data storage and reporting methods at transportation agencies rely on linear referencing methods (LRMs); consequently, GPS data must be able to link with linear referencing. Unfortunately, the two systems are fundamentally incompatible in the way data are collected, integrated, and manipulated. In order for the spatial data collected using GPS to be integrated into a linear referencing system or shared among LRMs, a number of issues need to be addressed. This report documents and evaluates several of those issues and offers recommendations. In order to evaluate the issues associated with integrating GPS data with a LRM, a pilot study was created. To perform the pilot study, point features, a linear datum, and a spatial representation of a LRM were created for six test roadway segments that were located within the boundaries of the pilot study conducted by the Iowa Department of Transportation linear referencing system project team. Various issues in integrating point features with a LRM or between LRMs are discussed and recommendations provided. The accuracy of the GPS is discussed, including issues such as point features mapping to the wrong segment. Another topic is the loss of spatial information that occurs when a three-dimensional or two-dimensional spatial point feature is converted to a one-dimensional representation on a LRM. Recommendations such as storing point features as spatial objects if necessary or preserving information such as coordinates and elevation are suggested. The lack of spatial accuracy characteristic of most cartography, on which LRM are often based, is another topic discussed. The associated issues include linear and horizontal offset error. The final topic discussed is some of the issues in transferring point feature data between LRMs.