#9877 closed (fixed)
More Pythonic mutations of geometry objects
Reported by: | Owned by: | jbronn | |
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Component: | GIS | Version: | 1.0 |
Severity: | Keywords: | ||
Cc: | Triage Stage: | Accepted | |
Has patch: | yes | Needs documentation: | no |
Needs tests: | no | Patch needs improvement: | no |
Easy pickings: | no | UI/UX: | no |
Description
Experimenting with geodjango, I found myself immediately wanting easier,
more Pythonic ways to manipulate the data in the GEOS geometry objects:
geometryObj[i:j] = ((33.42,-70.89),(34.819,-67.61))
So I have extended the LineString and LinearRing classes' __getitem__
and
__setitem__
methods to allow slicing, added a __delitem__
while I was at it, and threw in most
of the non-special, standard list methods as well.
I'd like to do this for the geometry collections next, but I'm posting
this here (is there a better place?) to solicit feedback on these mods
before I continue.
Questions
- Is there some really good reason not to do this that I'm missing, or am
I just the first one who wanted it enough to sit down and do it?
- Did I do this correctly? It seems to work. I tested the correctness of
the mutations themselves, but haven't extensively tested the GEOS
methods on the mutated objects.
- I've created a situation where
del geometryObj[:] # now works geometryObj = LinearString([]) # doesn't work
Is there some reason I shouldn't do that?
- Does it make sense to implement similar mutation methods for
Point
objects or Polygon
objects?
- I think it would be nice to make the
LinearRing
mutations fool-proof.
Meaning since the first and last point must be the same, a LinearRing
object with n points should really behave like a list of n - 1
coordinates, all the while maintaining the last coordinate as a mirror of
the first so that the geometry won't be invalidated by the mutations.
Comments?
- I implemented
count()
which is redundant with__len__()
and, in this
case, num_points()
. Overkill?
- Also I'm not sure if
index(x)
andremove(x)
made sense in this
context, but I could imagine cases where they might be useful and so I
erred on the side of implementing as much of the standard list interface as
I thought reasonable. Comments?
- The
sort()
andreverse()
methods don't seem applicable here. These are the
only standard list methods which I did not implement. However, I think
that they might apply to the geometry collections. Comments?
Attachments (3)
Change History (10)
by , 16 years ago
Attachment: | pythonic_mutation_patch_part_I added |
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by , 16 years ago
Attachment: | pythonic_mutation_patch_part_I.2 added |
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This is an updated patch to Django 1.0.2 release
comment:1 by , 16 years ago
Regarding question 2 above, I've attached an updated patch with additional tests checking that the following GEOS properties work as expected on the mutated geometries:
num_coords,
empty,
valid,
simple,
ring,
boundary,
convex_hull,
extend,
area,
length
comment:2 by , 16 years ago
I've completed a second round of modifications and am attaching a patch which supersedes the previous patches.
I modified the GeometryCollection
class with list-like, slice-enabled mutations. I then refactored the code, placing the bulk of the modifications in a ListMixin
class, which I added as a superclass to both LineString
and GeometryCollection
. I'm sure a similar mixin exists already somewhere (the UserList
module did not seem to be appropriate) but I didn't know where to look.
I also modified the tests (with a little bending backwards) to exercise both the geometries and the geometry collections. Currently the tests operate on LineString
, LinearRing
, MultiPoint
, and MultiLineString
.
I am still relatively new both to Django and to Python, so I'd love some feedback on style, etc.
by , 16 years ago
Attachment: | pythonic_mutation_patch_part_II added |
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More complete list-style mutations for Geometry Collections; refactored code
comment:3 by , 16 years ago
Note that the pythonic_mutation_patch_part_II
attachment is also a patch to the django 1.0.2 release and supersedes the patches I attached earlier.
comment:4 by , 16 years ago
milestone: | → 1.1 |
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comment:5 by , 16 years ago
Owner: | changed from | to
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Status: | new → assigned |
Triage Stage: | Unreviewed → Accepted |
comment:6 by , 16 years ago
Resolution: | → fixed |
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Status: | assigned → closed |
(In [10131]) Refactored the GEOS interface. Improvements include:
- Geometries now allow list-like manipulation, e.g., can add, insert, delete vertexes (or other geometries in collections) like Python lists. Thanks, Aryeh Leib Taurog.
- Added support for GEOS prepared geometries via
prepared
property. Prepared geometries significantly speed up certain operations. - Added support for GEOS cascaded union as
MultiPolygon.cascaded_union
property. - Added support for GEOS line merge as
merged
property onLineString
, andMultiLineString
geometries. Thanks, Paul Smith. - No longer use the deprecated C API for serialization to/from WKB and WKT. Now use the GEOS I/O classes, which are now exposed as
WKTReader
,WKTWriter
,WKBReader
, andWKBWriter
(which supports 3D and SRID inclusion) - Moved each type of geometry to their own module, eliminating the cluttered
geometries.py
. - Internally, all C API methods are explicitly called from a module rather than a star import.
This is a patch to the django 1.0.2 release