Contour plot is empty due to internal reprojection issue

hvPlot
1

I have some data that I want to get a contour plot from. This is my code (the data is open source):

import xarray as xr
import hvplot.xarray
import cartopy.crs as ccrs

ds = xr.open_dataset('http://geoport.usgs.esipfed.org/thredds/dodsC/bathy/etopo1_bed_g2')

na = ds.topo.sel(lon=slice(-130,-50),lat=slice(15,50))   # North America
na = na.where(na < 0)
na = na.where(na > -1000)

contours = na.hvplot.contour(x='lon', y='lat', levels=5, cmap=['#000000'], 
                             geo=True, crs=ccrs.PlateCarree())
contours

This creates an empty plot with the warning:

WARNING:param.project_path: While projecting a Contours element from a PlateCarree coordinate reference system (crs) to a PlateCarree projection none of the projected paths were contained within the bounds specified by the projection. Ensure you have specified the correct coordinate system for your data.

However, if I plot that same data as a quadmesh, it plots fine and the projection is correct.

na.hvplot.quadmesh(x='lon', y='lat', rasterize=True, geo=True, project=True, cmap='viridis', frame_width=800, crs=ccrs.PlateCarree())

Also, if I add project=True to the contour plot, I get this error:

File /home/conda/global/d346bceda0a73e0d4a1d000f6e408ff98f97300889e28f2363f683db19a0f74c-20230620-190627-268969-5-hytest-workshop/lib/python3.10/site-packages/holoviews/plotting/bokeh/element.py:903, in ElementPlot._update_ranges(self, element, ranges)
    901 if fixed_height:
    902     plot.frame_height = height
--> 903     plot.frame_width = int(height/aspect)
    904     plot.width, plot.height = None, None
    905 elif fixed_width:

ValueError: cannot convert float NaN to integer

Am I doing something wrong on the contours plot or is this a bug?

2

I don’t think you are doing anything wrong and I would expect it to work. This seems to work for me:
contours = na.hvplot.contour(x='lon', y='lat', levels=5, cmap=['#000000']).opts(projection=ccrs.PlateCarree())

Can you please open an issue on hvplot with a small MRE example (maybe lanXlon with a size of 10X10)

ValueError: cannot convert float NaN to integer is another issue. I don’t know if it is Holoviews or hvplot, though. Maybe try to search and see if you can find an issue. If not, please open an issue on hvplot too.

3

Ah, you removed geo=True. If you add that back in to your example, it no longer works and will create an empty plot with the projection warning above.

na.hvplot.contour(x='lon', y='lat', levels=5, cmap=['#000000'], geo=True).opts(projection=ccrs.PlateCarree())
4

Ok, I see where the issue is coming from. contour can’t handle the NaNs in the dataset. The original dataset will contour fine, but when I did

na = na.where(na<0)
na = na.where(na>-1000)

I introduced NaNs which aren’t being handled properly.

I’ll open an issue on hvplot.

5

We need to update our contouring code to use contourpy anyway. Could you file an issue with the bug on HoloViews and suggest we rewrite the operation using contourpy?

1 Like
6

Done: Contour doesn't handle NaNs properly · Issue #5779 · holoviz/holoviews · GitHub