Great Lakes Bathymetry

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

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

Create STL for CNC Router or 3D Printer

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. Right-click component under Component Tree, then select Properties
9. Switch to 3D view so the changes are illustrated
10. Move Shape Height slider until desired relief is achieved (1.5" was used for this project)
11. Open unadjusted .tiff in Inkscape (one with dark image with little detail, but sharp boundary edge)
12. Choose Path -> Trace Bitmap
    • Use Brightness Cutoff with the lowest possible settings
    • Deselect Smooth
13. Choose Path -> Outset to increase size so bitmap is tightly enveloped by vector (may need to adjust outset steps under Preferences -> Steps)
14. Erase any holes within the vector to create solid object
15. Import vector in Aspire and carefully align to .tiff
16. Move to Toolpaths bar and select 3D Roughing Path
17. Choose Selected Vector under Machining Limit Boundary, then press Calculate
18. Press 3D Finishing Toolpath, then choose vector as above
19. Preview the toolpaths to ensure desired results
20. 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

Open Source Workflow

1. Download ArcGrid DEM from USGS National Map or Earth Explorer (3DEP, 1/3 arc-second DEM)
2. Unzip file
3. Open QGIS, add Vector, add layer file (.adf)
4. Select extent (Raster -> Extraction -> Clipper)
5. Save as GeoTIFF
6. Add GeoTIFF to model
7. Analyze to DEM (Raster -> Analysis -> DEM [Terrain Models])
8. 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)

Very Long, Detailed Workflow

1. Download QGIS
2. Download Great Lakes Bathymetry from NOAA's Grid Extract Tool
3. Download lakes shapefiles from Science Base
4. Open shapefiles in QGIS and merge each at border
   1. Open first file, e.g. hydro_p_LakeErie.shp
   2. Right click in Layers Panel and save as LakeEriebound
   3. Remove original shapefile
   4. Repeat for all needed
   5. Select LakeEriebound in Layers Panel, click Select Features by area or single click
   6. Hold shift, select both features in LakeEriebound on map
   7. Click Toggle Editing (pencil icon)
   8. Go to Edit -> Merge Selected Features
   9. Check that LakeEriebound is now one polygon, Toggle Editing, save changes, then repeat for all shapefiles
5. Go to Vector -> Geoprocessing Tools -> Fixed distance buffer
6. Run as batch process by inputting each shapefile (LakeEriebound, etc.) into Input Layer, and buffer name (e.g. eriemask) in Buffer column. Used .2 Distance
7. Remove LakeEriebound, etc. from Layers Panel
8. Add bathymetry rasters from NOAA's Grid Extract Tool, ensuring all area under buffers is included
9. Rename Buffer to eriemask, etc.
10. Go to Raster -> Extraction -> Clipper
11. Choose first lake input file and name output file (e.g. eriebath)
12. Choose mask layer and select relevant mask (e.g. eriemask)
    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
13. Go to Raster -> Miscellaneous -> Merge and select two adjacent masked files

[Running into issues with shared color values]

Laser Cut, Low Resolution

Workflow

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

Other Sources

• Earth satellite imagery from USGS, esp. those over time
• ArcGIS contour map of the Great Lakes
• 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