[Qgis-user] finding the radius of a curve

[Cory Albrecht]

I tried saving a few layers that had arcs and circles (x,y, r coords), but
QGIS converts each curve to a bunch of straight line segments instead of
saving them as curves. :-(

On Mon, Apr 22, 2019 at 3:33 AM McDonaldR <McDonaldR at angus.gov.uk> wrote:

> As your data is in PostGIS and assuming that they are arcs (curved lines
> part of a circle) you could use some geometry and spatial SQL functions to
> calculate the radius of any curve knowing the coordinates of the end points
> of the curve.
>
>
>
> To quote the pseudo code on the linked page:
>
>
>
> “To calculate the radius of an arc, take the height -- "H" -- of the arc
> and divide it by two. Call the result "C." Now take the width -- "W" -- of
> the arc and square it by multiplying it by itself. Call the result "D."
> Next multiply height, "H," by eight and call this result "E." Divide "D" by
> "E" and call the result "F." The radius of the arc is C plus F.”
>
>
>
> https://sciencing.com/calculate-radius-curve-7804090.html
>
>
>
> Could probably be wrapped in a function and run against any curve.
>
>
>
> Ross
>
>
>
> *From:* Qgis-user [mailto:qgis-user-bounces at lists.osgeo.org] *On Behalf
> Of *Cory Albrecht
> *Sent:* 19 April 2019 17:08
> *To:* qgis-user at lists.osgeo.org
> *Subject:* Re: [Qgis-user] finding the radius of a curve
>
>
>
> I'll give it a try. Thanks!
>
>
>
> On Sun, Apr 14, 2019 at 7:52 AM Mike Flannigan <mikeflan at att.net> wrote:
>
>
> Draw a circle and measure the diameter/radius.
>
> Maybe use this plugin to create a circle:
> https://plugins.qgis.org/plugins/CADDigitize/
>
>
> Mike
>
>
> On 4/13/2019 2:00 PM, qgis-user-request at lists.osgeo.org wrote:
> > Hello all,
> >
> > I'm looking for a way to find the radius of a curve (for roads,
> railyways)
> > in QGIS. If it were a paper map I could do it with a drafting compass
> > (calipers to some) and a ruler, but this is a PostGIS layer.
> >
> > Any plugin recommendations or links to a set of steps to accomplish this?
> > Thanks in advance!
>
>
>
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