4
You can directly use the GDAL contour polygons tool. It is available from GDAL version 2.4.0. To see which GDAL version your QGIS installation uses go to Menu Help / About, see screenshot. If installed, it looks like this:
If you have GDAL >= 2.4.0, but the entry contour polygons does not appear in the QGIS processing toolbox, you can use the "...
3
As your DEM seems to be in a geographic CRS ( EPSG:4326 ; WGS84), the unit of measurement is in degrees, not in meters. So measurements of length do not make sense: your cellsize is 0.0002777 degrees.
Reproject your DEM to a projected CRS to have meters as measurement unit.
2
Problem is that contour lines may not be closed, so it's hard to create the polygons.
Simplest GDAL way seems to me classify the raster and then polygonize it.
gdal_calc.py --calc='(A<=30)*30+(A>30)*A//5*5' --outfile=classified.tif -A input.tif
The calc expression turns all values less than 30 to 30, and greater values are rounded to the floor ...
2
The output extend you defined is quite weird:
'TARGET_USER_XMIN TARGET_USER_XMAX TARGET_USER_YMIN TARGET_USER_YMAX' : '-93.137700000,-93.137400000,45.008800000,45.009000000 [EPSG:26915]'
You use EPSG:26915 (NAD83 / UTM zone 15N), but your coordinates seem to be in EPSG:4326. The coordinates -93.137700000,45.008800000 in EPSG:26915 are located somewhere in ...
1
Create a polygon named delete for the region you want to delete from the raster (unneeded region, in orange on the screenshot below).
Create a polygon extent (red outline polygon) that covers the extent of your raster using Menu Processing / Toolbox / Create layer from extent and set the raster as input.
Cut out shape of delete from the polygon extent ...
1
Get a polygon layer of the water surface, for example from OpenStreetMaps (OSM). See here how to download: https://gis.stackexchange.com/a/368774/88814. Another option is to use the QuickOSM plugin. You can use the OpenStreetMap tags natural=water (red on the screenshot) and natural=bay (blue).
You will get many very small water features, so probably you ...
1
I found a solution for this in R:
I created a uniform raster with all cells at elvetion 1
Using the function "xyFromcell" in the "raster" package I created separate rasters of latitude and of longitude of the uniform raster
I conducted a raster calculation of the form [f(x) = mx + b] using the slope and the intercept from the line ...
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