Mailing List Archive: Shapely Polygon creating empty polygon

Shapely Polygon creating empty polygon

Jan 4, 2022, 2:57 PM

Post #1 of 3 (194 views)

I’m running into an issue with shapely that is baffling me. Perhaps someone here can help out?

When running shapely directly from a python 3.8 interpreter, it works as expected:

>>> import shapely
>>> shapely.__version__
'1.8.0'
>>> from shapely.geometry import Polygon
>>> bounds = [-164.29635821669632, 54.64251856269729, -163.7631779798799, 54.845450778742546]
>>> print(Polygon.from_bounds(*bounds))
POLYGON ((-164.2963582166963 54.64251856269729, -164.2963582166963 54.84545077874255, -163.7631779798799 54.84545077874255, -163.7631779798799 54.64251856269729, -164.2963582166963 54.64251856269729))

However, if I put this exact same code into my Flask app (currently running under the Flask development environment) as part of handling a request, I get an empty polygon:

>>> import shapely
>>> print(shapely.__version__)
>>> from shapely.geometry import Polygon
>>> print(Polygon.from_bounds(*bounds))

Output:

1.8.0
POLYGON EMPTY

In fact, *any* attempt to create a polygon gives the same result:
>>> test = Polygon(((1, 1), (2, 1), (2, 2)))
>>> print(test)
POLYGON EMPTY

What am I missing here? Why doesn’t it work as part of a Flask request call?
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

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Re: Shapely Polygon creating empty polygon [ In reply to ]

python at mrabarnett

Jan 4, 2022, 4:47 PM

Post #2 of 3 (192 views)

Permalink

On 2022-01-04 22:57, Israel Brewster wrote:
> I’m running into an issue with shapely that is baffling me. Perhaps someone here can help out?
>
> When running shapely directly from a python 3.8 interpreter, it works as expected:
>
>>>> import shapely
>>>> shapely.__version__
> '1.8.0'
>>>> from shapely.geometry import Polygon
>>>> bounds = [-164.29635821669632, 54.64251856269729, -163.7631779798799, 54.845450778742546]
>>>> print(Polygon.from_bounds(*bounds))
> POLYGON ((-164.2963582166963 54.64251856269729, -164.2963582166963 54.84545077874255, -163.7631779798799 54.84545077874255, -163.7631779798799 54.64251856269729, -164.2963582166963 54.64251856269729))
>
> However, if I put this exact same code into my Flask app (currently running under the Flask development environment) as part of handling a request, I get an empty polygon:
>
>>>> import shapely
>>>> print(shapely.__version__)
>>>> from shapely.geometry import Polygon
>>>> print(Polygon.from_bounds(*bounds))

In that piece of code you didn't set 'bounds'. It might be worth setting
it or at least printing it out to double-check.
>
> Output:
>
> 1.8.0
> POLYGON EMPTY
>
> In fact, *any* attempt to create a polygon gives the same result:
>>>> test = Polygon(((1, 1), (2, 1), (2, 2)))
>>>> print(test)
> POLYGON EMPTY
>
Did you try that piece of code both in Flask and from the command line,
again to double-check.

> What am I missing here? Why doesn’t it work as part of a Flask request call?
>
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Re: Shapely Polygon creating empty polygon [ In reply to ]

ijbrewster at alaska

Jan 5, 2022, 9:48 AM

Post #3 of 3 (192 views)

Permalink

Found it! Apparently, it’s an import order issue. This works:

>>> from shapely.geometry import Polygon
>>> from osgeo import osr
>>> bounds = [-164.29635821669632, 54.64251856269729, -163.7631779798799, 54.845450778742546]
>>> print(Polygon.from_bounds(*bounds))
POLYGON ((-164.2963582166963 54.64251856269729, -164.2963582166963 54.84545077874255, -163.7631779798799 54.84545077874255, -163.7631779798799 54.64251856269729, -164.2963582166963 54.64251856269729))

But this doesn’t:

>>> from osgeo import osr
>>> from shapely.geometry import Polygon
>>> bounds = [-164.29635821669632, 54.64251856269729, -163.7631779798799, 54.845450778742546]
>>> print(Polygon.from_bounds(*bounds))
POLYGON EMPTY

…So apparently I have to make sure to import shapely *before* I import anything from osgeo. Why? I have no idea...
---
Israel Brewster
Software Engineer
Alaska Volcano Observatory
Geophysical Institute - UAF
2156 Koyukuk Drive
Fairbanks AK 99775-7320
Work: 907-474-5172
cell: 907-328-9145

> On Jan 4, 2022, at 1:57 PM, Israel Brewster <ijbrewster@alaska.edu> wrote:
>
> I’m running into an issue with shapely that is baffling me. Perhaps someone here can help out?
>
> When running shapely directly from a python 3.8 interpreter, it works as expected:
>
> >>> import shapely
> >>> shapely.__version__
> '1.8.0'
> >>> from shapely.geometry import Polygon
> >>> bounds = [-164.29635821669632, 54.64251856269729, -163.7631779798799, 54.845450778742546]
> >>> print(Polygon.from_bounds(*bounds))
> POLYGON ((-164.2963582166963 54.64251856269729, -164.2963582166963 54.84545077874255, -163.7631779798799 54.84545077874255, -163.7631779798799 54.64251856269729, -164.2963582166963 54.64251856269729))
>
> However, if I put this exact same code into my Flask app (currently running under the Flask development environment) as part of handling a request, I get an empty polygon:
>
> >>> import shapely
> >>> print(shapely.__version__)
> >>> from shapely.geometry import Polygon
> >>> print(Polygon.from_bounds(*bounds))
>
> Output:
>
> 1.8.0
> POLYGON EMPTY
>
> In fact, *any* attempt to create a polygon gives the same result:
> >>> test = Polygon(((1, 1), (2, 1), (2, 2)))
> >>> print(test)
> POLYGON EMPTY
>
> What am I missing here? Why doesn’t it work as part of a Flask request call?
> ---
> Israel Brewster
> Software Engineer
> Alaska Volcano Observatory
> Geophysical Institute - UAF
> 2156 Koyukuk Drive
> Fairbanks AK 99775-7320
> Work: 907-474-5172
> cell: 907-328-9145
>

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