What is Building Footprint?
Building footprint has been defined by many authors and researchers but in general Remote Sensing and GIS terms it can be defined as “the outline or the outer boundary of the intersection of the building and the ground as it can be observed in optical satellite and aerial imagery”
But the catch here is that Satellite imageries can give us a view of every property contained in the area of interest-Unless there is tree/canopy present. Few of the new research and special algorithms have helped to display the outline of structure on a property or its building footprint without being limited by the landscape and other items impeding satellite imageries.
What are the methods to generate Building Footprints?
The building footprints of a particular area of interest can be generated by 3 methods:
- Manual Method
- Semi-Automated Method
- Automated Method
1- Manual Method:
- This includes manual on-screen digitizing efforts
- The process can be very time consuming and work is labor-intensive
- A high level of expertise is NOT needed.
- The level of experience digitizer/ operator can have is an effect on the speed of digitization.
- Though manual error is present, results can be controlled and with higher accuracy.
2- Semi-Automated Method:
- The combination of mixed data resources are used
- Accuracy is highly dependent upon the segmentation, image quality, shadow, and other properties
- Removal of canopy/vegetation structure is a bit tedious process
- Once the process is fixed, it can be tried in different areas which can help to assess the accuracy.
- The technical expertise required is high.
3- Automated Method:
- The combination of mixed data resources are used including high resolution imageries with LiDAR
- Generally, Object based classification of high resolution images is used to extract built-up areas and then analyzing the LiDAR point clouds to shape roofs within the built-up areas.
- As compared to manual digitizing efforts , automated building footprint extraction required relatively less time.
- Expertise level and testing required on large number of datasets. In cases of errors, manual digitization can be introduced to increase accuracy.
Whether for planning, compliance or development building footprints data have become one of the most valuable sources of information. Many municipalities have incorporated building footprints which have helped to create dataset including information which can be updated on a timely basis. Few of the benefits of building footprints includes:
- Confirmation of the exact location of the primary buildings which is supported by rooftop geocoding and geofencing applications.
- Helpful for identifying number of buildings present on given parcel.
- Tax parcel mapping indicating information about tax collected with respect to location.
- Identification of building hazards for any mishaps
- Creating immediate response and preparedness plans in terms of natural / man made hazards.
Here is the open data provided by the City of New York
Building footprint is that the most simple info necessary for evaluating the vulnerabilities of a building for a particular hazard. It represents a complete space of a building and provides a higher description of its spatial characteristics compared to a degree illustration in terms of spatial location, form, distribution, floor house quantitative relation and relationship between buildings and different objects (topological, orientation, proximity, etc.).
Once building footprints square measure obtainable, attribute info like its number of floors, use, occupancy etc. can be added for using them for vulnerability and risk analysis.