Hydrographic Survey of Kiskatinaw River Marries Drone 3D Landscape with Bathymetric Survey Data in Geospatial 3D PDF Report

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.

Figure 1 Google image of Arras Weir

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.

About Hydrasurvey

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.

References

  1. Kiskatinaw River Background https://en.wikipedia.org/wiki/Kiskatinaw_River
  2. 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
  3. 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
  4. Hydrasurvey Ltd. hydrasurvey.ca
  5. Pix4D Mapper https://www.pix4d.com/product/pix4dmapper-photogrammetry-software
  6. Sonarwiz https://chesapeaketech.com/products/sonarwiz-sidescan/
  7. 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:

  1. obj (3D land mesh)
  2. mtl (Material file, reference by OBJ)
  3. jpg (Land image composite used by OBJ)
  4. grd (Bathymetry data grid)
Figure 2 First Enable Probe and process the OBJ file on its own, locate the 0,0 position. In this case is shown near the Drone launch point. Then click on an identifiable common point at West end of weir, to find a common position offset. Note and remember these offset values. Similarly, the GRD can be converted on its own, and the probe can be used to find the same place as the West end of the weir, where the projected UTM offset will be shown as imported from the GRD file.

 

Figure 3 Load both the OBJ and GRD files into the input list, enable options and set the DCC and GRD interfaces, respectively. This allows for specifying individual conversion settings per file.

 

Figure 4 On the PDF 3D View tab, set the view scheme to Geospatial, Insert controls for 3D probe (compact) and UTM/UPS mode. This will enable extra tools in the PDF.

 

Figure 5 On the Geospatial tab, select the OBJ mesh in the drop-down selector menu. Then open the Coordinate system, and set Projected:PCS for NAD83(CSRS) / UTM zone 10N (EPSG:3157) zone. This will insert the geospatial coordinates inside the PDF file for the probe reporting.

 

Figure 6 On the Visual Effects tab, select and specify a rainbow colour-map file from the samples/colormaps/ folder. Change the Legend title from Elevation to Depth.

 

Figure 7 Now go to the Interface Settings tab, enable the Object Position option, and specify X and Y coordinate system offsets appropriate for placing the OBJ mesh into the UTM Zone. This is not needed for GRD since it already has the correct offset specified in the file.

 

Figure 8 Also in Interface Settings, use the top drop-down to select the GRD bathymetry file. At the bottom of this menu, set a custom elevation scale to “-1” since this positive numbers mean depth.

 

Figure 9 Finally the Conversion is performed and a new 3D PDF created. The probe can be used to further check the model details, depth and distance within the 3D scene.

 

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