Re: [mapserver-users] scalebar wrong with epsg:3857

2018-01-29 Thread b.j.kobben 
This could be map distortion easily. What latitude is the mile x mile box you 
are showing on...? 

--
Barend Köbben
 

On 29/01/2018, 00:07, "Richard Greenwood"  wrote:

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,  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" 
 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  












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




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Re: [mapserver-users] scalebar wrong with epsg:3857

2018-01-28 Thread 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,  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-boun...@lists.osgeo.org on behalf of
> richard.greenw...@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 
>
>
>
>
>
>


-- 
Richard W. Greenwood, PLS
www.greenwoodmap.com
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Re: [mapserver-users] scalebar wrong with epsg:3857

2018-01-28 Thread b.j.kobben 
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" 
 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 





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