scalebar wrong with epsg:3857

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scalebar wrong with epsg:3857

rgreenwood
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

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Richard W. Greenwood, PLS
www.greenwoodmap.com

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Re: scalebar wrong with epsg:3857

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


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Barend Köbben
 

On 28/01/2018, 20:36, "mapserver-users on behalf of Richard Greenwood" <[hidden email] on behalf of [hidden email]> 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>





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Re: scalebar wrong with epsg:3857

rgreenwood
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, <[hidden email]> 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" <[hidden email] on behalf of [hidden email]> 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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Re: scalebar wrong with epsg:3857

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

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Barend Köbben
 

On 29/01/2018, 00:07, "Richard Greenwood" <[hidden email]> 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, <[hidden email]> 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" <[hidden email] on behalf of
[hidden email]> 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> <http://www.greenwoodmap.com>












--
Richard W. Greenwood, PLS
www.greenwoodmap.com <http://www.greenwoodmap.com>




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