Decision Guide: Ground or Aerial Survey?
Quick Answer: Both!
Detailed topographic mapping from our MapWarehouse archives is popular with civil engineers to model terrain in 3D. Users can predict the flow of surface water, air movement, acoustic modeling, sight line analysis, make volumetric calculations, and even show depth on a flat image when used together with orthophoto. Most big projects, however, also have a ground survey component. Why buy DEM or contour mapping if you need a survey anyway? One's not better than the other, they both have their place in the project life cycle. Take a detailed look:
Regardless of what type of project you have, it will go through these basic steps:
1. Initiation - Developing a concept, studying feasibility
2. Planning - Designing in detail, planning permissions
3. Execution - Construction proceeds
4. Monitoring and Control - Operation and maintenance
5. Closure - Removal and disposal
So, where does aerial and survey data fit in the project life cycle? In general, aerial data, being a little less detailed (1m contour intervals) than a ground survey, is the first look option. Ground survey takes place later on.
Let's imagine the project begins with an RFP/RFQ, and within any proposal will be a scope of work and overviews of timelines, deliverables etc. One of the first decisions that needs to be finalized before moving ahead is location. This is where aerial data makes the most sense. Many sites can be rejected or short listed using map based tools to measure distances (to utility tie ins, nearby structures etc) and areas (buildable areas, economic potential etc) before investing in ground surveys. Researching land information with imagery avoids the hassle and cost of visiting multiple remote locations. Once a site is selected, only then is a ground survey worth while.
Services such as MapCast or VuMAP allow users to browse detailed geographic data like high resolution imagery and elevations across Southern Ontario with a predictable cost. The information is available immediately as needed and gives a good overview of the ground conditions around a potential site.
Map based tools can help estimate costs for materials and other resources needed in the next phases of the project. For example, roofing and paving material costs that are closely tied to square footage. Understanding the costs quickly provides an advantage in negotiating and bidding.
Before approvals can be granted to begin the construction, a more detailed analysis must take place to investigate the projects' impact on the environment and to determine the site's cultural importance. Building on the location intelligence gained in the site selection phase, this phase relies heavily on detailed ground surveys.
Aerial data plays a supporting role in the permitting process. Surveys can be confusing to non-technical stakeholders in your project, so including high quality map-scaled imagery can provide much needed context to communicate complex spatial information easily. You'll often see aerial imagery as a backdrop to surveys in applications for municipal approvals.
Construction and Beyond
The execution phase relies on maps and surveys for reference, which may need periodic updating to ensure the project is on track and once the project is complete. Detailed site specific land surveys aren't usually necessary to repeat through the operational lifespan of the infrastructure. Aerial imagery is collected periodically for large areas that can assist in maintenance scheduling for very large infrastructure projects over time.
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