Shobhit Chandra

LiDAR-Derived High Quality Ground Control Information and DEM for Image Orthorectification

Orthophotos (or orthoimages if in digital form) have long been recognised as a supplement or alternative to standard maps. The increasing applications of orthoimages require efforts to ensure the accuracy of produced orthoimages. As digital photogrammetry technology has reached a stage of relative maturity and stability, the availability of high quality ground control points (GCPs) and digital elevation models (DEMs) becomes the central issue for successfully implementing an image orthorectification project. Concerns with the impacts of the quality of GCPs and DEMs on the quality of orthoimages inspire researchers to look for more reliable approaches to acquire high quality GCPs and DEMs for orthorectification. Light Detection and Ranging (LiDAR), an emerging technology, offers capability of capturing high density three dimensional points and generating high accuracy DEMs in a fast and cost-effective way. Nowadays, highly developed computer technologies enable rapid processing of huge volumes of LiDAR data. This leads to a great potential to use LiDAR data to get high quality GCPs and DEMs to improve the accuracy of orthoimages. This paper presents methods for utilizing LiDAR intensity images to collect high accuracy ground coordinates of GCPs and for utilizing LiDAR data to generate a high quality DEM for digital photogrammetry and orthorectification processes. A comparative analysis is also presented to assess the performance of proposed methods. The results demonstrated the feasibility of using LiDAR intensity image-based GCPs and the LiDAR-derived DEM to produce high quality orthoimages.

Drainage network modelling for Water-Sensitive Urban Design.

While drainage network models may be relatively easy to assemble as a prerequisite to site selection for infrastructure supporting suburbanisation with Water-Sensitive Urban Design (WSUD), this is unlikely to be the case if the terrain is very subdued. Both ab initio and retro-fit WSUD implementation for such terrain refers, in the first instance, to a drainage network model that includes information on the scope for optimising residential space while conforming to: (1) statutory planning rules about the provision of public open space; and (2) WSUD drainage network design such that runoff waters are retained long enough to allow at least temporary storage. It is shown in this research that a technique applied to condition a LiDAR DEM can accurately model the drainage network of a basin at the land-parcel scale. The drainage network for ab initio WSUD is best defined using multi-flow modelling, with the relative significance of stream segments indicated by their stream order derived using the Strahler method. In contrast, when applying the retro-fit WSUD, the relative significance of segments given by the Shreve stream order method was found to be more useful. The approaches described in this article are designed to support the initial site planning stage and avoid the need for immediate and expensive detailed field survey. At the same time they can be deployed to show how much scope there is for WSUD retro-fit in established housing areas up-stream of an infill development area. Thus, basin-wide appraisal is facilitated and the need for earthmoving is minimised.