[mapserver-users] scalebar wrong with epsg:3857

[Richard Greenwood]

This is a larger error than simple map distortion. See screen shot below.
The orange dashed lines are a grid of 1 mile x 1 mile (5280 feet). The
upper scale bar that says "5000 ft" is generated by OpenLayers and is
pretty good. The lower scale bar is generated by MapServer is off by 25% to
30%.


​

On Sun, Jan 28, 2018 at 1:37 PM, <b.j.kobben at utwente.nl> wrote:

> No scalebar is ever correct on any map if the map is not having an 'equal
> area' (sometimes called 'equivalent') projection -- meaning the areas are
> comparable/not distorted over the map. The 3857, being a Mercator
> projection is not, and indeed here the distortions reach from none at the
> equator to huge at the poles (officially endless - theoretically the poles
> are points, but depicted as lines...)
>
> The software you use makes no difference, although some specialised ones
> let you show distortions using indicators called Tissot-indicatrices)
>
> http://kartoweb.itc.nl/geometrics/
> https://en.wikipedia.org/wiki/Tissot%27s_indicatrix
>
>
> --
> Barend Köbben
>
>
> On 28/01/2018, 20:36, "mapserver-users on behalf of Richard Greenwood" <
> mapserver-users-bounces at lists.osgeo.org on behalf of
> richard.greenwood at gmail.com> wrote:
>
> The scalebar created by MapServer 4.6 is too short when I'm using
> epsg:3857. I'm guessing that it's correct at the equator and gets worse as
> you get further north or south? Has anyone else experienced this and
> possibly have a solution?
>
>
> Thanks,
> Rich
>
>
> --
> Richard W. Greenwood, PLS
> www.greenwoodmap.com <http://www.greenwoodmap.com>
>
>
>
>
>
>


-- 
Richard W. Greenwood, PLS
www.greenwoodmap.com
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