Ground Survey

INTRODUCTION: (vertical) between objects, measuring the direction of line between objects and the angles between lines. It has been the time-honored approach to mapping  features and boundaries, to calculating areas and subdividing areas and to drawing up cross-sections for land management, construction, and a host of other applications. It used to be that all maps were compiled using  land-surveying techniques, but for the past 50 years has been supplemented first by aerial photography and then by satellite remote sensing to increase the speed and cost-effectiveness with which maps and now digital coverage’s can be compiled. Nevertheless, land surveying remains the most accurate.

Again the microchip, together with GPS and the ability to generate and measure the return signal from beams of infrared and laser light, land surveying has been revolutionized almost beyond recognition. The equipment has become considerably automated while software is used to carry out the calculations. Land surveying has also become digitally integrated with GPS and remote sensing to form automated systems for data integration and production (Grejner-Brzezinska et al., 2004).

While land surveying, GPS, and remote sensing provide geometric data, field surveys are carried out to sample check (ground truth) automated mapping methods, to collect more detailed attribute data, and as a means of monitoring changes to attribute data. While some attributes can be collected during a land survey or from remote sensing, many attributes tend to be collected separately and from a range of sources. Key to field surveys these days are mobile GIS deployed using personal digital assistants (PDA) or tablet PCs. This has come about due to the increasing power of PDA, their wireless connectivity, the availability of add-on GPS, and the increasing sophistication of the GIS software that can be installed. The position of the field operative can be displayed in relation to base mapping, thematic overlays, and remote sensing imagery; attributes can be entered through a series of customized data entry forms that do preliminary onsite checking of consistency so that gross errors (or blunders) can be rectified before moving on.

This digital approach allows new data to be checked and integrated into the main database more quickly(Wagtendonk and de Jeu, 2007). Another form of ground survey that has risen in popularity in recent years is the drive-by survey (see, for example, Google Street View). This is a field survey technique in which a vehicle is equipped with high accuracy differential GPS, laptop(s), pen tablets (for digital note taking), voice recording (also for annotation), roof-top digital cameras or video providing 360o view, and wireless communication. The vehicle is then driven along road networks. and even off-road while an operative supervises the recording of new data and changes to the existing database.

Nontraditional approaches to Data Collection:The ever-growing need for automated and cost-effective methods of spatial and attribute data collection with improved granularity is fostering the development of nontraditional techniques. Closed-circuit television (CCTV), although technically a form of remote sensing, is used for recording traffic and people flow rates. However, a range of roadside and inroad devices using radar, acoustic sensors, and infrared detectors are being increasingly deployed not only to count traffic and pedestrians round-the-clock, but also to classify the traffic into vehicle types and to determine levels of congestion so as to provide near-instant warnings of events that are happening on our roads. Laurini et al. (2001) have classified this type of spatial data collection where remote sensors telemeter data across fixed-line or wireless links to an operations center that is monitoring some spatial phenomenon (e.g., weather, river flow, traffic flow, transport of hazardous materials) as TeleGeoInformation.