From Burundi to WGS84 issue...

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05-29-2013 12:07 PM
HarmenKampinga
New Contributor III
I am having a problem with a conversion I'll share that here. Who can help?

We have recieved some spatial data from Burundi. Therefore it has a geographic coordinate system. Unfortunately I am not able to convert it to WGS84. Whatever I try, there is always a shift in the geodata of several meters.

More details:

We are working in Esri ArcGIS 10.1. We also tried to convert the data with Quantum GIS.
In both cases the results were not accurate.

Extra information on our activities/settings:
The transformation we used is an international standard:
http://georepository.com/transformation_3998/Arc-1960-to-WGS-84-4.html
The specifications of this transformation is the same as of Arc 1950 to WGS 1984 number 3.

Quantum GIS and Esri ArcGIS are telling us that the projection of the data is "User Defined". The systems do not recognize the projection as a known projection system.

> Quantum GIS: USER:100000 -  * Auto generated CRS (+proj=tmerc +lat_0=0 +lon_0=30 +k=0.9996 +x_0=500000 +y_0=10000000 +a=6378249.145 +b=6356514.966398753 +towgs84=-143,-90,-294,0,0,0,0 +units=m +no_defs)

> Esri ArcGIS:
GK_Burundi
Authority: Custom

Projection: Gauss_Kruger
False_Easting: 500000,0
False_Northing: 10000000,0
Central_Meridian: 30,0
Scale_Factor: 0,9996
Latitude_Of_Origin: 0,0
Linear Unit: Meter (1,0)

Geographic Coordinate System: GCS_Arc_1950
Angular Unit: Degree (0,0174532925199433)
Prime Meridian: Greenwich (0,0)
Datum: D_Arc_1950
  Spheroid: Clarke_1880_Arc
    Semimajor Axis: 6378249,145
    Semiminor Axis: 6356514,966395495
    Inverse Flattening: 293,466307656

And I just want a simple transformation from this projection to WGS84 :)
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2 Replies
MelitaKennedy
Esri Notable Contributor
Hello,

There isn't much information available for that part of the world. EPSG (http://www.epsg.org - I'm on the subcommittee that maintains it) thinks that the transformation, Arc 1950 to WGS 1984 (3) is incorrect. That Burundi data was on Arc 1960 instead. There's another transformation, Arc 1960 to WGS 1984 (4). You might try defining your data as Arc 1960 with the projection information you have and use that transformation.

None of the transformations that I know about in that area are very good.

Cliff Mugnier in his Grids & Datums column on Burundi lists a GK zone for Burundi that has a scale factor of 1.0, not 0.9996, so that's something else to try.

Melita
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HarmenKampinga
New Contributor III
Hello,

There isn't much information available for that part of the world. EPSG (http://www.epsg.org - I'm on the subcommittee that maintains it) thinks that the transformation, Arc 1950 to WGS 1984 (3) is incorrect. That Burundi data was on Arc 1960 instead. There's another transformation, Arc 1960 to WGS 1984 (4). You might try defining your data as Arc 1960 with the projection information you have and use that transformation.

None of the transformations that I know about in that area are very good.

Cliff Mugnier in his Grids & Datums column on Burundi lists a GK zone for Burundi that has a scale factor of 1.0, not 0.9996, so that's something else to try.

Melita


Thank you Melita for your quick reply!
I will have a look at it and will let you know the outcome.
Harmen
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