Converting Geographic Coordinate System

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03-14-2017 10:05 AM
GurpreetPadda
New Contributor II

Hello - I found some 2011, 2012, 2013 and 2014 shp files on a government website. 2011 and 2012 were delivered in BNG coordinate system and the other 2 were in GCS_ETRS_1989 coordinate system. I have tried converting these to BNG through the arctoolbox/projections and transformations/project but nothing changes - even though the 'properties' box states BNG coordinate system. I've also tried to convert these in ArcMap/properties etc. but the 'properties' box states BNG, but the projections are still different to the 2011 and 2012 projections. Can someone help?

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GurpreetPadda
New Contributor II

I would like this projection with the data source and and coordinate extents below in the 3 illustrations:

Data Type:               Shapefile Feature Class

Shapefile:                \\ueahome\eresssf1\esg11dgu\data\Documents\Gurpreet Padda\Gurpreet PhD\ENV Department\GIS\Spatial analysis\Rectangles\2011fishingvesseldensitytest.shp

Geometry Type:      Polygon

Coordinates have Z values:     No

Coordinates have measures:  No

 

Projected Coordinate System:               British_National_Grid

Projection:               Transverse_Mercator

False_Easting:        400000.00000000

False_Northing:      -100000.00000000

Central_Meridian:   -2.00000000

Scale_Factor:          0.99960127

Latitude_Of_Origin:                49.00000000

Linear Unit:             Meter

 

Geographic Coordinate System:            GCS_OSGB_1936

Datum:    D_OSGB_1936

Prime Meridian:      Greenwich

Angular Unit:           Degree

 

Unfortunately, what I am getting is this:

Data Type:               File Geodatabase Feature Class

Database:                \\ueahome\eresssf1\esg11dgu\data\Documents\ArcGIS\Default.gdb

Feature Class:         c2014fishingvesseldensity_Pr2

Feature Type:          Simple

Geometry Type:      Polygon

Coordinates have Z values:     No

Coordinates have measures:  No

 

Geographic Coordinate System:            GCS_OSGB_1936

Datum:    D_OSGB_1936

Prime Meridian:      Greenwich

Angular Unit:           Degree

 

 

Can anyone provide step by step instructions on how to convert the geographic and projected coordinates so I get the very first illustration?

 

Sorry and thank you.

ps - print screen didn't work, so I have attached a word doc.

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PROBERT68
Regular Contributor III

You can use Microsoft OneNote to capture Screenshot if you have on your computer.

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MelitaKennedy
Esri Notable Contributor

Hi Gurpreet, 

The word doc didn't make it that I can see. Anyway, Robert Pollack showed one way to create a copy of the data in the coordinate system that you want. Set the data frame's coordinate system to what you want, set any geographic (datum) transformation (data frame properties > coordinate system tab, transformations button), and right-click the layer in the table of contents and select data > export data. 

The other method is to use the Project tool (Data Management toolbox, Projections and Transformations toolset). 

However, if you're not able to add the original datasets into ArcMap and have them all line up / overlay more-or-less (within a 100 meters or so), there's something wrong. 

You said that you reprojected some of them to BNG, but they still didn't line up. That often occurs when the coordinate system on the original dataset is incorrect--someone defined it incorrectly. 

So if you look at the extents of the original data, you should be able to check whether a BNG (coordinates in the xxxxxx range) or OSGB36/ETRS89 (coordinates with x or xx, ex. longitude=1.123456, latitude=53.123456). If the coordinates don't look right, the coordinate system definition is wrong.

Melita

GurpreetPadda
New Contributor II

Hello all - thanks for your help with this matter. I've tried and tested a lot of them.

I found someone within my organisation to help me with the conversion, although instead of converting, it seemed to unveil another fundamental problem altogether. Agree the problem is with the original source data which is preventing the grids from matching up. This is supplemented by the fact that the internal GIS expert has also encountered similar problems with converting from the European grid to the british national grid. For some reason, and in some cases, the two grid systems do not marry. There are alternative solutions that I am planning on exploring which involves analysing my data in point format as oppose to polygons.

Thanks anyway!

NeilAyres
MVP Frequent Contributor

Whether it's polygon or point format will not make any difference if there is another fundamental problem with how the coordinate system has been defined (and if that CS is actually wrong).

I think you should resolve that first.

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