Choose not to generate vis image at night?

[Cris B]

Hi

I'd like to prevent true colour (and also greyscale vis) images from being generated when it is night time, and also perhaps for instances when there are only a few "lit" pixels. What's the most efficient way of doing this with a satpy.scene.Scene instance? I'm imagining something like this, but it takes quite a while to compute:

array = list(scn_resampled.values())[0]

num_pixels = np.prod(array.shape)

# 5% threshold

thresh = 0.05 * num_pixels

num_lit_pixels = (array.compute() > 0).sum()

if num_lit_pixels > thresh:

    scn_resampled.save_dataset(...)

Cheers

Cris

[Panu Lahtinen]

On 23.9.2024 23.25, 'Cris B' via pytroll wrote:
> Hi
>
> I'd like to prevent true colour (and also greyscale vis) images from
> being generated when it is night time, and also perhaps for instances
> when there are only a few "lit" pixels. What's the most efficient way
> of doing this with a satpy.scene.Scene instance? I'm imagining
> something like this, but it takes quite a while to compute:

Hi,

This is what we do in Trollflow2 to check day-light coverage:

https://github.com/pytroll/trollflow2/blob/main/trollflow2/plugins/__init__.py#L767

The relevant parts are

overpass = Pass(platform_name, start_time, end_time, instrument=sensor)

and calling the

_get_sunlight_coverage(area_def, start_time, overpass=None)

function to get the actual percentage where sun is up on the target
area. We then compare to configured values and discard the product if
the day-light covered area is too small or too small (for night-only
products).


P

--
Arctic Space Centre
Finnish Meteorological Institute
Phone: +358 50 380 3261

[Cris B]

Great, thanks very much Panu.

I'm only using geo imagery so I guess all I need is to import  _get_sunlight_coverage and use?

It's not clear to me how to install trollflow2 into my conda environment. conda search can't find trollflow. Please could you suggest how?

Thanks

[Cris B]

No worries, I got it using 'pip install trollflow2'

[Gerrit Holl]

Hi,

trollflow2 is not in conda-forge. You need to install it with pip
from pypi or directly from the git repo.

regards,
Gerrit.

On Tue, 24 Sept 2024 at 10:51, 'Cris B' via pytroll

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[Panu Lahtinen]

On 24.9.2024 11.51, 'Cris B' via pytroll wrote:
> Great, thanks very much Panu.
>
> I'm only using geo imagery so I guess all I need is to import 
> _get_sunlight_coverage and use?

Sorry for being a bit late, got entangled in work.

You shouldn't import and use private functions (their names starting
with "_") from any package, they are an implementation detail that might
change without any notice. I would instead just copy the relevant parts
to your own wrapper script