Completing the Elevation Model of Wellington

I’ve recently been working more in HEC-RAS and decided to have a bit of fun. Since I had already built a 3D model of  Wellington for my 3D printing project I thought, why not make some crazy flooding scenarios of the city.

However, before I could get started there was still a problem with the terrain model. The model was based off of the 1m DEM from LINZ which cut off water bodies at the water surface level. While it isn’t actually necessary have the bathymetry data for overland flooding, I wanted to have the option of dropping the waterline below sea level and also capture more realistic water depths. 

After a lot of searching I was not able to find detailed bathymetry data for the Wellington Harbour and Fitzroy Bay readily available. After contacting NIWA and they were able to provide me with a 10 meter DEM for most of Wellington Harbour and parts of Fitzroy Bay shown below. 

I merged the bathymetry data with my terrain model, and most of Wellington Harbour was complete but there were still large gaps in the channel leading into the harbour and Fitzroy Bay (lower left). Using sounding point and contour data for reference, I interpolated the missing areas in the terrain (lower right).


The animation below shows the difference between my old terrain model and the new model with the harbour bed incorporated.

I’ll note that this is a hobby project, and data is not a final or official production, but it will serve for my purposes.

Results from a preliminary flooding model are shown in the following video. Do not panic, this is the result of me throwing close to 40 meters of water at Fitzroy Bay, a rather unlikely event.

Play time aside, I’m looking forward to building multiple scenarios using project sea-rise levels and sharing those in a later post.

2D Raster to 3D prints

Growing up, I spent a lot of my time building models, dioramas, and train sets; dreaming about taking the craft to ever smaller scales. Flash forward several year, and I purchase my first FDM 3D printer. Naturally, I started pushing the limits of its resolution designing and printing some cool mini’s in the 1:1000 scale range:

Pretty good, however, I knew the precision of the FDM would be a limiting factor for anything more than “impressionist” models. Time warp a couple more years, and I get my first SLA/DLP printer. With an XY resolution of 47 microns (half a human hair) and Z layering to 15 microns (a grain of pollen thick), I would finally be able to get to scales I once dreamed about. I first tested the printer with models  which had failed on the FDM printer.

Promising start, but I more recently decided trying something new; printing an area from the real world. For the first test, I borrowed a raster from one of our coastal projects which has 0.2 meter DEMs. The raster was converted to an .stl file with at a scale of 1:4100 (approximately matching the max XY resolution of the printer). I decided to slice the layers at the minimum thickness (15 microns) to see what I would get. About 4 hours of printing later, and I’m pleasantly surprised with the results:

Considering the scale you’re able to clearly make out the small bumps of the terrain, where streams and washouts are, and even where a hiking trail crosses the area to wind up the hillside. Looking at the layers compared to my thumb print, you can see that several could fit between one groove.

Feeling bold I decide to go a step further. This time, I found a polylayer of Wellington that includes the approximate height and elevation of building, convert it to a 1m DEM raster, and merge it with the 1m Wellington elevation DEM.

I then exported and converted the central Wellington area at three different scales: 1:40,000, 1:20,000, and 1:10,000.

Again, I’m quite pleased with the results. Despite some artifacts de-laminating and attaching to areas they shouldn’t (particularly for the 1:20,000 scale print), the detail is impressive. I was particularly pleased to see the small houses on the hillsides, even at 1:40,000 scale.

Overall, I felt like the test runs were a success. Based on this experience; I’ve ordered in some new printing resins more appropriate for the detail I’m after, and have adjusted the slicing to avoid de-laminating. Until I have new and improved prints to show, I’ll leave this as a parting bonus, the results of the terrain print after some painting and flocking fun.

Logan Ashmore