Hi Roman,
I'm not sure how you would determine the kill time. Each individual call to
GetFeatureCount is fairly quick, but when you're doing it a lot, in a loop,
they add up. Here's an example output from the Python profiler:
ncalls tottime percall cumtime percall filename:lineno(function)
195 98.689 0.506 98.690 0.506 {built-in method
osgeo._ogr.Geometry_Intersection}
4091 40.792 0.010 40.860 0.010 {built-in method
osgeo._ogr.Geometry_Union}
8358 33.862 0.004 33.862 0.004 {built-in method
osgeo._ogr.Layer_GetFeatureCount}
28653 17.059 0.001 17.115 0.001 {built-in method
osgeo._ogr.Layer_GetNextFeature}
Obviously, I could be calling the feature count less often, but I was hoping I
could shave a small amount of time off each call. Also obviously, my geometry
operations are more costly than the feature operations, but it's worth trying
to save time anywhere you can.
Jon
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From: Roman Breitfuss-Schiffer <[email protected]>
Sent: 20 January 2022 10:38
To: Jon Morris <[email protected]>; [email protected]
Subject: Re: [gdal-dev] Faster alternative to GetFeatureCount?
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Hi Jon!
I don't know if there's an alternative to GetFeatureCount. At least I couldn't
find one in the API documentation. Maybe there's a workaround I'm not aware
of...
What you could do is wrap the call of GetFeatrueCount in a function which is
killed after some time (2 approaches are discussed here:
https://stackoverflow.com/questions/40915527/kill-function-after-a-given-amount-of-time).
With that approach the question remains of getting the value of
GetFeatureCount when the function gets killed. One could assume that there are
more features than 1 if the function takes too long. This assumption might be a
bit risky though...
Best regards
Roman
Am 20.01.2022 um 10:00 schrieb Jon Morris:
I'm writing applications using the GDAL Python bindings and when I profile for
performance, GetFeatureCount frequently comes out near the top. I'm often using
it to check whether a spatial or attribute filter has returned any features and
don't need the full count. When the layer contains millions of features, there
would be a big performance improvement if we could exit the count early.
Is there a better way of doing this? I've tried using GetNextFeature instead,
but there must be quite a lot of overhead in that function as it is much
slower. All I need to know is if the layer has has 0, 1 or >1 features, I don't
need the actual count. Can anyone suggest the fastest way of doing this in
Python? I'm using GDAL 3.3.1 at the moment but could upgrade if there is new
functionality that would help.
Thanks,
Jon
Jon Morris
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