#17736: django.contrib.gis.geos.polygon from_bbox loss of floating-point
accuracy
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Reporter: tdihp@… | Owner: nobody
Type: Bug | Status: new
Component: GIS | Version: 1.3
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Changes (by claudep):
* needs_better_patch: => 0
* component: Uncategorized => GIS
* needs_tests: => 0
* needs_docs: => 0
Comment:
In any case, whenever you are using floating-point values, rounding will
occur at some point. Currently, from_bbox uses the Python built-in str
which defaults to 12 significant digits. Of course, you can always do the
rounding yourself. For example, to keep 25 significant numbers:
{{{
>>> l,t,r,b = 0.0,0.0,format(math.pi, '.25f'), format(math.pi, '.25f')
>>> Polygon.from_bbox((l,t,r,b)).coords
(((0.0, 0.0),
(0.0, 3.1415926535897931),
(3.1415926535897931, 3.1415926535897931),
(3.1415926535897931, 0.0),
(0.0, 0.0)),)
}}}
So even with 25 significant numbers, it seems GEOS rounds to 16. Should
from_bbox also default to 16 significant digits?
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Ticket URL: <https://code.djangoproject.com/ticket/17736#comment:1>
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