[QGIS-Developer] Suggestion of a different perpendicularSegment geometry method

[Nyall Dawson]

On Thu, 22 Oct 2020 at 16:35, Tobias Schmetzer <tschmetzer at gmx.de> wrote:
>
> Good point. I can do plain doubles as well of course if that makes it more flexible.
>
> Regarding the length of the perpendicular:
> I think the most common use case is to just create any perpendicular with the least computation power. For somebody requiring a specific length I could add an optional "segment length" argument for controlling the
> length of the perpendicular line.
> What do you think of using a length argument of 0 for a normalized length? (No idea if somebody would need that)

Sounds good to me!

Nyall

>
> Viele Grüße, Tobias
> Am 22.10.20, 08:12 schrieb Nyall Dawson <nyall.dawson at gmail.com>:
>>
>> On Thu, 22 Oct 2020 at 06:43, Tobias Schmetzer <tschmetzer at gmx.de> wrote:
>> >
>> > Dear developer colleagues,
>> >
>> > I'm new to QGIS development and my cpp and git experience is a long
>> > while ago. Yet I want to make the effort to contribute to this project
>> > in return for using it for months.
>> >
>> > During my python scripting I was missing a function that I created
>> > for myself in python which I would need to split a polyline using
>> > QgsGeometry.splitGeometry().
>> >
>> > The function I want to contribute will create a perpendicular segment to
>> > a given segment with it's center at a given point (the already available
>> > function QgsGeometryUtils.perpendicularSegment doesn't fullfill that need)
>> >
>> > I would suggest to add to the cpp code of QgsGeometryUtils. A good old
>> > friend of mine and cpp expert will do the first code review once it's
>> > finished before I do the PR.
>> >
>> > I am already working on that function and its test. The header looks
>> > like this:
>> >
>> > /**
>> > * \brief Create a perpendicular line segment to a given segment
>> > * [segmentPoint1, segmentPoint2] with its center at centerPoint
>> > * May be used to split geometries
>> > * \param centerPoint Point where the center of the perpendicular should
>> > * be located
>> > * \param segmentPoint1 The segment's start point
>> > * \param segmentPoint2 The segment's end point
>> > * \returns A line (segment) centered in point p and perpendicular to
>> > * segment [segmentPoint1, segmentPoint2]
>> > */
>> >
>> > static QgsLineString perpendicularCenterSegment( const QgsPoint &point,
>> > const QgsPoint &segmentPoint1, const QgsPoint &segmentPoint2 ) SIP_HOLDGIL;
>>
>> Looks good to me! Some suggestions:
>> - instead of accepting QgsPoint values, consider making the arguments
>> plain doubles instead. (e.g. double segmentPoint1x, double
>> segmentPoint1y, etc). This makes the API more flexible because callers
>> who have QgsPointXY or some other input values don't need to do a
>> conversion to QgsPoint first.
>> - For the same reasons, consider making the method return 4 doubles
>> instead of a QgsLineString. E.g. add double& perpendicular1x SIP_OUT,
>> double &perpendicular1y SIP_OUT, double& perpendicular2x SIP_OUT,
>> double &perpendicular2y SIP_OUT. This again avoids the forced use of
>> QgsLineString, and will reap benefits if the function is called many
>> times and the caller does not need a QgsLineString object
>> - Do you need to add a "segment length" argument for controlling the
>> length of the perpendicular line generated?
>>
>> Nyall
>>
>>
>> >
>> > Any comments or did I even miss an already available
>> > function for what I am suggesting?
>> >
>> > Kind regards, Tobias
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