[Qgis-user] finding the radius of a curve

[Andreas Neumann]

Hi Cory,

Not if you use a file-format that supports arcs: Geopackage, Postgis, 
Interlines, GML. Maybe also FGDB (but not sure if OGR supports curves 
for that format).

Greetings,

Andreas

Am 29.04.19 um 18:21 schrieb 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 
> <mailto: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
>     <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 <mailto: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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