Great Lakes Bathymetry

Partial Erie bathymetry cut with MPCNC, map from NOAA, processed with QGIS and Aspire 8.5

Create Model for CNC Router

QGIS Workflow

1. Download QGIS
2. Download Great Lakes Bathymetry from NOAA's Grid Extract Tool by choosing "Great Lakes Bathymetry," selecting the then drawing a rectangle around the area
3. Download greatlakes_subbasins.zip from Science Base
4. Merge sections
   1. In QGIS, add subbasins.shp as Vector Layer
   2. Click Toggle Editing (pencil icon)
   3. Ctrl +A to select all elements
   4. Go to Edit -> Merge Selected Features
   5. Check that subbasins is now one polygon, Toggle Editing, save changes
5. Add bathymetry rasters from NOAA's Grid Extract Tool, ensuring all area under buffers is included
6. Merge images: Raster -> Miscellaneous -> Merge
7. Choose raster files and name output file (e.g. greatLakes)
8. Go to Raster -> Extraction -> Clipper
9. Choose mask layer (greatLakes) and select subbasin mask
   1. If error Output driver `GMT' not recognised . . ., select pencil button next to output algorithm and change -of GMT to -of GTIFF
   2. If black 0-level box appears after masking, delete the files and re-run with large (-99999) number and No Data Value box selected

Proprietary Workflow (Aspire)

Video walkthrough here

1. Data pulled from NOAA's ETOPO1 images, available directly here which offers a 1-minute resolution of worldwide bedrock
2. Add raster image to QGIS
3. Select extent desired (Raster -> Extraction -> Clipper)
4. Export as .tiff
5. Open in GIMP, click white area surrounding with Magic Wand Tool, then drag upward to increase threshold to maximum
6. Overwrite .tiff to save
7. Open in Aspire, under Modeling tab, select "Create a component from selected bitmap"
8. Switch to 3D view so the changes are illustrated
9. Right-click component under Component Tree, then select Properties
10. Move Shape Height slider until desired relief is achieved (.95" was used for this project)
11. Return to Drawing View. With image selected, choose Trace Bitmap (bird image under "Create Vectors")
12. Increase threshold until outline only is left
13. Switch to Toolpaths bar and select 3D Roughing Path
14. Choose Selected Vector under Machining Limit Boundary, then press Calculate
15. Press 3D Finishing Toolpath, then choose vector as above
16. Preview the toolpaths to ensure desired results
17. If image is larger than machine, use Tile Toolpaths to divide it

Tool speeds used in above (wooden) image:

Print Pass	Tool Size	Feed Rate	Plunge Rate	Print Time
Rough Pass	.25" square bit	15.0 mm/sec	3.0 mm/sec	1:30
Finish Pass	.125" ball nose	25.0 mm/sec	6.0 mm/sec	4:30

STL for 3D Printing

1. Open QGIS, add Vector, add layer file (.adf)
2. Select extent (Raster -> Extraction -> Clipper)
3. Save as GeoTIFF
4. Add GeoTIFF to model
5. Analyze to DEM (Raster -> Analysis -> DEM [Terrain Models])
6. If necessary, merge the DEMs

• A balance must be made between extent and resolution. 1:50,000 creates excellent models, but cannot contain an entire lake. Above that and the file crashes my system. A further note on resolution.

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• Solution to bathymetric (negative) altitude values: using Raster Calculator, add bottom value to all height values

1. Create STL (Raster -> DEMto3D)

Laser Cut, Low Resolution

1. Download shapefiles from NOAA. Superior bathymetry contours with unclear provenance is available here, with login
2. Download and install QGIS and Inkscape
3. No need to extract files, open each in QGIS Desktop
4. Add OpenStreetMap information if desired (the native support is not working at this time, but the plugin does)
5. Right-click shapefile in left layers panel, select Properties
6. Choose Filter, then create expression, e.g. "DEPTH" IN ('0', '1', '25', '50', '60')
   • It is helpful to use the Values box (make sure "Use unfiltered layer" is checked if changing an applied filter) to see the extent of the map's values

Ideas

• Process of creating a 3D map of the area
• Try this map with these instructions
• For OSM information, use Geofabrik.de and reformat if necessary as described here

Resources

• Downloadable Great Lakes bathymetric maps from NOAA
• All bathymetric maps from NOAA
• The USGS Earth Explorer is easier to use than the above, but requires a login and download client
• Natural Earth provides shapefiles for cultural and physical elements
• Index of one arc-second images from NASA's Shuttle Radar Topography mission

Other Sources

• Earth satellite imagery from USGS, esp. those over time
• ArcGIS contour map of the Great Lakes
• Earth Explorer (3DEP, 1/3 arc-second DEM)
• Live Access Servers hosted by NOAA/PMEL/TMAP provide information on air quality, ocean salinity, temperature, etc.
• LIDAR resources in case we want to machine it. I want to machine it.
• BBBike.org pulls from OSM, but extent is much too small.
• Using plywood (though very heavy) with the proper scale would approximate the contour lines of a topo map...
• Mosaicing and clipping rasters
• OceansMap, a well-aggregated set of realtime data about major bodies of water around the world, including the Great Lakes region
• Historical maps from the Army Corps of Engineers
• Portal for Great Lakes Observing System information from the Integrated Ocean Observing system
• The National Map combines many of the above resources, including ArcGrid DEM from USGS