Issue overlapping model data to Google map background

[alessandroanav]

Hello,

I would overlap my model data to Google map using salem but I am facing an issue when I use data on its original grid. However, if I regrid data to WRF grid the program works perfectly, so I do not understand why on the native grid the script doesn't work. Any help to understand if I am doing something wrong or there is a bug in the code is greatly appreciated.

Please find below the relevant code.

I open and read the netcdf data with xr.open_dataset, which returns:

Dimensions: (time: 1, lon: 4320, lat: 2160)
Coordinates:

• time (time) datetime64[ns] 8B 2023-06-10
• lon (lon) float32 17kB -180.0 -179.9 -179.8 ... 179.8 179.9 180.0
• lat (lat) float32 9kB 89.96 89.88 89.79 89.71 ... -89.79 -89.88 -89.96
  Data variables:
  fldout (time, lat, lon) float32 37MB ...

---

To check if data are recognized correctly by salem, I make a quick map with salem.quick_map(varname="fldout"). As data are displayed correctly, I assume salem recognizes the model grid.

Then, I download the google map over a region of interest:

g                     = GoogleVisibleMap([0, 20.0], y=[20, 60]],
                                         scale=2,  
                                         maptype='satellite',use_cache=True)  

and transform model grid to the new map, as suggested in this script (https://salem.readthedocs.io/en/v0.3.4/auto_examples/plot_googlestatic.html):

sm                    = Map(g.grid, factor=1, countries=False)
x, y                  = sm.grid.transform(lon, lat)

At the end I try to overlap the data to the google map but, as you can see, the model grid does not match the google map.

Any insight of this problem?

[fmaussion]

Hello and sorry for the delay. GoogleMaps are not meant to be overlaid with gridded data, but with vector files. That being said, sm.set_data() should still work and be preferable to transforming your data yourself.

Finally, as of today Salem will not be supporting google maps without a personal API key. See https://developers.google.com/maps/documentation/maps-static/get-api-key

I will now update the documentation to that effect.

[alessandroanav]

Thanks fro the suggestion, it worked fine.

Now, I am attempting to customize the plot, masking values below a given threshold, but I realized the following commands do not work with salem. In particular, this command:

data = np.where( data<200, np.nan, data)

gives the following error message:
ValueError: Dimensions of data do not match the map.

While I do not know how to reproduce this into salem:
cmap.set_bad(alpha = 0.0) # NaN values are transparent

Is there any equivalent command?

Thanks again for the support