# Proj4Projection : problem with epsg 3857

**URL:** <https://community.thinkgeo.com/t/proj4projection-problem-with-epsg-3857/3659>\
**Category:** WPF\
**Created:** [May 16, 2014, 9:38am UTC](https://community.thinkgeo.com/t/proj4projection-problem-with-epsg-3857/3659 "2014-05-16T09:38:07Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Steph](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/s/22d042/32.png) [@Steph](https://community.thinkgeo.com/u/Steph)\
**Post date:** [May 16, 2014, 9:38am UTC](https://community.thinkgeo.com/t/proj4projection-problem-with-epsg-3857/3659/1 "2014-05-16T09:38:07Z")

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Hi,&nbsp;  
I&nbsp;have&nbsp;a&nbsp;problem&nbsp;with&nbsp;Proj4Projection.  
  
  
I&nbsp;reproject&nbsp;a&nbsp;shapefile&nbsp;layer&nbsp;and&nbsp;the&nbsp;result&nbsp;is&nbsp;different&nbsp;if&nbsp;false.  
  
  
  
**Code&nbsp;1&nbsp;:&nbsp;** &nbsp;(this&nbsp;one&nbsp;give&nbsp;a&nbsp;false&nbsp;result)  
projectionAffichage&nbsp;=&nbsp;bingmap&nbsp;(epsg=3857)  
internalprojection&nbsp;is&nbsp;wgs84&nbsp;(epsg&nbsp;4852)  
  
  
  
_string&nbsp;externalProjection&nbsp;=&nbsp;Proj4Projection.ConvertPrjToProj4(Proj4Projection.ConvertEpsgToPrj(projectionAffichage));_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(internalProjection&nbsp;!=&nbsp;externalProjection)_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Proj4Projection&nbsp;proj4Projection&nbsp;=&nbsp;new&nbsp;Proj4Projection();_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;proj4Projection.InternalProjectionParametersString&nbsp;=&nbsp;internalProjection;_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;proj4Projection.ExternalProjectionParametersString&nbsp;=&nbsp;externalProjection;_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;shpFile.FeatureSource.Projection&nbsp;=&nbsp;proj4Projection;_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}_  
  
  
  
The&nbsp;result&nbsp;of&nbsp;projection&nbsp;is&nbsp;&nbsp;ie&nbsp; **Proj4Projection\_String\_20140516.jpg**  
  
  
  
  
  
  
Code&nbsp;2&nbsp;:&nbsp;(this&nbsp;one&nbsp;give&nbsp;a&nbsp;good&nbsp;result)  
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;_&nbsp;&nbsp;public&nbsp;Proj4Projection&nbsp;ReProjectionEntreeSortie(int&nbsp;projEntree,&nbsp;int&nbsp;projSortie)_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;{_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Proj4Projection&nbsp;projectionSridAffichage&nbsp;=&nbsp;new&nbsp;Proj4Projection(projEntree,projSortie);_  
  
  
  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;if&nbsp;(!projectionSridAffichage.IsOpen)&nbsp;projectionSridAffichage.Open();_  
  
  
  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;return&nbsp;projectionSridAffichage;_  
_&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;}_  
The&nbsp;result&nbsp;of&nbsp;projection&nbsp;is&nbsp;&nbsp;ie&nbsp; **Proj4Projection\_Int\_20140516.jpg**  
  
  
  
  
  
I&nbsp;think&nbsp;that&nbsp;the&nbsp;problem&nbsp;comes&nbsp;from&nbsp;"Proj4Projection.ConvertPrjToProj4(Proj4Projection.ConvertEpsgToPrj(projectionAffichage)).&nbsp;"  
  
Because&nbsp;the&nbsp;result&nbsp;in&nbsp;the&nbsp;application&nbsp;is&nbsp;&nbsp;+proj=merc&nbsp;+lon\_0=0&nbsp;+k=1&nbsp;+x\_0=0&nbsp;+y\_0=0&nbsp;+ellps=WGS84&nbsp;+datum=WGS84&nbsp;+units=m&nbsp;+no\_defs&nbsp;  
  
  
  
On&nbsp;this&nbsp;website&nbsp;the&nbsp;proj4&nbsp;is&nbsp;ie&nbsp;**[spatialreference.org/ref/sr-org/epsg3857/proj4/](http://spatialreference.org/ref/sr-org/epsg3857/proj4/)**  
  
With&nbsp;the&nbsp;code&nbsp;2,&nbsp;I&nbsp;have&nbsp;this&nbsp;proj4.  
  
  
  
I&nbsp;hope&nbsp;my&nbsp;explanation&nbsp;is&nbsp;clear.  
Regards.  
  
  
  
Steph.  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
[Proj4Projection\_String\_20140516.jpg](https://community.thinkgeo.com/uploads/default/original/1X/81534e3363797f9ac68f3c5fb3986ba7f0a44144.jpg) (55.5 KB)  
[Proj4Projection\_Int\_20140516.jpg](https://community.thinkgeo.com/uploads/default/original/1X/be8b3195c2fed9d384b4390fb5cf7860836fc31a.jpg) (35.9 KB)

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<div class="post-metadata">

**Author:** ![Troy](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/t/85f322/32.png) [@Troy](https://community.thinkgeo.com/u/Troy)\
**Post date:** [May 19, 2014, 1:20am UTC](https://community.thinkgeo.com/t/proj4projection-problem-with-epsg-3857/3659/2 "2014-05-19T01:20:59Z")

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Hi&nbsp;Steph,  
  
  
  
I&nbsp;tested&nbsp;this&nbsp;case&nbsp;with&nbsp;the&nbsp;below&nbsp;codes&nbsp;and&nbsp;found&nbsp;something:

> `string externalProjection1 = Proj4Projection.ConvertPrjToProj4(Proj4Projection.ConvertEpsgToPrj(3857));`  
> `string externalProjection2 = Proj4Projection.ConvertPrjToProj4(File.ReadAllText(@"....\3857.prj")); `  
> `string externalProjection3 = Proj4Projection.GetEpsgParametersString(3857);`

  
The&nbsp;result&nbsp;is&nbsp;the&nbsp;externalProjection2&nbsp;and&nbsp;externalProjection3&nbsp;are&nbsp;almost&nbsp;the&nbsp;same,&nbsp;but&nbsp;the&nbsp;externalProjection1&nbsp;is&nbsp;like&nbsp;your&nbsp;got,&nbsp;it&nbsp;is&nbsp;total&nbsp;difference&nbsp;with&nbsp;them.&nbsp;However,&nbsp;all&nbsp;of&nbsp;the&nbsp;three&nbsp;can&nbsp;match&nbsp;with&nbsp;GoogleLayer(EPSG:3857)&nbsp;when&nbsp;I&nbsp;reproject&nbsp;a&nbsp;4326&nbsp;shape&nbsp;file&nbsp;to&nbsp;the&nbsp;3857&nbsp;with&nbsp;the&nbsp;above&nbsp;string.&nbsp;As&nbsp;you&nbsp;said&nbsp;you&nbsp;are&nbsp;using&nbsp;4852&nbsp;source&nbsp;file,&nbsp;I&nbsp;guess&nbsp;the&nbsp;externalProjection1&nbsp;can’t&nbsp;match&nbsp;with&nbsp;it.  
  
  
  
I&nbsp;guess&nbsp;using&nbsp;externalProjection2&nbsp;or&nbsp;externalProjection3&nbsp;should&nbsp;work&nbsp;in&nbsp;your&nbsp;end,&nbsp;would&nbsp;you&nbsp;please&nbsp;try&nbsp;it?  
  
Thanks,  
  
Troy  
  
[3857.zip](https://community.thinkgeo.com/uploads/default/original/2X/9/99415c7b1f112c399da803b4e621c68357c51fac.zip) (356 Bytes)

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<div class="post-metadata">

**Author:** ![Steph](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/s/22d042/32.png) [@Steph](https://community.thinkgeo.com/u/Steph)\
**Post date:** [May 22, 2014, 2:33am UTC](https://community.thinkgeo.com/t/proj4projection-problem-with-epsg-3857/3659/3 "2014-05-22T02:33:29Z")

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Hi&nbsp;Troy,&nbsp;&nbsp;  
&nbsp;&nbsp;  
&nbsp;With&nbsp;Proj4Projection.GetEpsgParametersString(3857),&nbsp;that&nbsp;works.&nbsp;  
&nbsp;Thanks.&nbsp;  
&nbsp;Regards.&nbsp;  
&nbsp;Steph.

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<div class="post-metadata">

**Author:** ![Troy](https://community.thinkgeo.com/letter_avatar_proxy/v4/letter/t/85f322/32.png) [@Troy](https://community.thinkgeo.com/u/Troy)\
**Post date:** [May 23, 2014, 12:28am UTC](https://community.thinkgeo.com/t/proj4projection-problem-with-epsg-3857/3659/4 "2014-05-23T00:28:55Z")

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Steph,&nbsp;  
&nbsp;&nbsp;  
&nbsp;Good&nbsp;to&nbsp;hear&nbsp;it&nbsp;helps.&nbsp;  
&nbsp;&nbsp;  
&nbsp;Thanks,&nbsp;  
&nbsp;Troy