[Qgis-user] finding the radius of a curve

[McDonaldR]

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<mailto: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<mailto: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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