Supplying water to the city of Dawson Creek British Columbia, the pool formed upstream of the Arras Weir is critical for municipal infrastructure management. Due to climate change and variable catchment flows, monitoring the flow and reservoir capacity is needed on a regular basis. The team at Hydrasurvey carried out a bathymetric survey project to assess the state of the riverbed upstream of the weir, and at the same time made an aerial 3D drone survey of the surrounding slopes and forest. For the client report, the Hydrasurvey team married a 3D land model with the sonar river depth data in an interactive 3D PDF report.
“Using ReportGen on this project for the 3D client report gave us an edge and a unique offering really appreciated by our client” noted Andrew Ambrocichuk, principle engineer, “this also helped our work-flow to merge different data types and apply geospatial reference at the point of PDF generation. We are now using 3D PDFs in many of our projects going forward”.
The Kiskatinaw River originates in the foothills of the Canadian Rockies. The Arras weir (seen in the centre of the google map image) holds water back from the otherwise fast-flow and creates a pool so there is something to draw from even when flows are low for the Dawson Creek city water supply. The weir was constructed in 1992, after a serious drought left the river levels so low that the intake pipe was no longer submerged.
In preparation for the final client report, the Hydrasurvey team married a full 3D photogrammetry reconstruction of the land area from the drone data with the sonar bathymetric data of the river bed. The completed report shows both in-situ with 3D interaction within an enriched 3D PDF report. The geographic coordinates of both the land and river data were aligned, and an additional geospatial probe and measurement tool was included within the PDF so clients can navigate and review spatial data without leaving the PDF report.
The land model was created by flying a UAV drone equipped with a digital camera to take 100s of high-quality photos of the river banks and surrounds in a structured flight pattern. The image collection was processed using Pix4D’s Mapper software, applying photogrammetry image reconstruction to create a 3D mesh with colour photographic overlay. The team selected the well-known OBJ format with a single JPEG composite texture at 8k x 8k pixel resolution, as this enabled flexibility in the choice of downstream report processing.
The hydrographic survey, the main purpose of the project, was conducted using side-scan and sub-bottom sonar equipment and the data was processed using Chesapeake Technology’s Sonarwiz software. After alignment, clean-up steps, a regular grid was created using the GRD gridded surface data format, with the zero-elevation point at the nominal river pool surface.
During the workflow for generating the 3D PDF, due to limitations of the OBJ file format, geospatial coordinate systems are not carried automatically; instead defining the local reference datum to a point near where the drown was launched. Uniquely, menus in the 3D PDF generation software ReportGen allowed these to be brought together and the projected UTM coordinate system applied, without requiring any external GIS software steps. By using a location probe within the 3D PDF, a common visual reference point was found (in this case the West-end of the weir).
More technical details of this workflow are described below to help any other survey or geospatial professionals creating a similar 3D PDF.
Hydrasurvey Ltd. (www.hydrasurvey.ca) specializes in wastewater lagoon sludge surveys, dredge project monitoring, hydrographic bridge surveys and underwater infrastructure imaging and inspection. Hydrasurvey’s goal is to eliminate uncertainty and reduce costs for municipal and industrial clients undertaking dredging and desludging projects through high accuracy sludge surveys and dredge project monitoring.
- Kiskatinaw River Background https://en.wikipedia.org/wiki/Kiskatinaw_River
- Dawson Creek Mirror article: Water supply conservation efforts have proven successful https://www.dawsoncreekmirror.ca/weir-science-helps-keep-dc-s-water-flowing-1.1306822
- Dawson Creek Mirror article: High Watershed Level Reported https://www.dawsoncreekmirror.ca/dawson-creek-news/months-after-floods-kiskatinaw-watershed-levels-highest-in-years-1.5057922
- Hydrasurvey Ltd. hydrasurvey.ca
- Pix4D Mapper https://www.pix4d.com/product/pix4dmapper-photogrammetry-software
- Sonarwiz https://chesapeaketech.com/products/sonarwiz-sidescan/
- PDF3D ReportGen Software https://www.pdf3d.com/products/pdf3d-reportgen/
Processing Step Details
The process of merging the OBJ and GRD files, and assigning the spatial corrections and geospatial UTM coordinates involves a step-by-step process, outlined here with menu illustrations. These are provided for other users who may wish to implement a similar workflow. Once the OBJ and GRD are created, only PDF3D ReportGen and the free Adobe Reader are involved.
This workflow uses four input files:
- obj (3D land mesh)
- mtl (Material file, reference by OBJ)
- jpg (Land image composite used by OBJ)
- grd (Bathymetry data grid)