[QGIS-Developer] Offset lines via qgis python

[Prem Kumar]

Hi Ujaval,

Thank you very much for pointing that out. That serves my purpose.

In fact, I had initially searched for a python implementation of the
Offsetlines processing tool but did not get it. Just a quick question, how
do we trace whether the processing tool implementation is in python or c++?

-Prem

On Wed, Jun 9, 2021 at 1:53 PM Ujaval Gandhi <ujaval at spatialthoughts.com>
wrote:

> You can look at the implementation
> <https://github.com/qgis/QGIS/blob/2d1aa68f0d044f2aced7ebeca8d2fa6b754ac970/src/analysis/processing/qgsalgorithmoffsetlines.cpp>
> of offsetline algorithm and you'll notice that it
> uses geometry.offsetCurve(). You can do the same in your code.
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> Ujaval Gandhi
> Spatial Thoughts
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>
> On Wed, Jun 9, 2021 at 1:31 PM Prem Kumar <prem.netgis at gmail.com> wrote:
>
>> Hi Team,
>>
>> Just wondering if there is a python api which gets an offset line or
>> parallel line (to both left and right sides) to a given line geometry in
>> Qgis Python. I know there exists a processing tool called Offsetlines
>> <https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectorgeometry.html#offset-lines> but
>> need this similar functionality at geometry object level so that I can
>> create offset lines only when needed based on my logic.
>>
>> The only way now is that I can perform the Offset lines on the entire
>> layer and then access the offset geometry if needed.
>>
>> On other hand, shapely has parallel_offset
>> <https://shapely.readthedocs.io/en/stable/manual.html#object.parallel_offset> but
>> this needs conversion from shapely geometry to qgisgeometry.
>>
>> Just looking for thoughts on this to optimize heavy geometry operations.
>> Appreciate your help.
>>
>> -Prem
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