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South Africa Projected Coordinate System   mohammed nazzal Oct 25, 2009
Re: South Africa Projected Coordinate Syste...   Melita Kennedy Oct 26, 2009
Re: South Africa Projected Coordinate Syste...   mohammed nazzal Oct 27, 2009
Re: South Africa Projected Coordinate Syste...   mohammed nazzal Oct 28, 2009
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Subject South Africa Projected Coordinate System 
Author mohammed nazzal 
Date Oct 25, 2009 
Message I'm having hard time locating the projected coordinate system for South Africa in ArcMap Library.

It is not listed in national grids (up to my knowledge). It's supposed to be (South Africa Survey Grid) and is based on WGS84.

Moreover, I don't know the parameters needed to create a new prj file.

This is the first time I find myself working in the southern half of the earth, and as silly as it sounds, I'm deeply confused ! It seems that whenever I import a surface for a region in South Africa from google earth to CAD or GIS, east becomes west and west becomes east !!!

I'm doing something the wrong way.. I just don't know what !!! I would appreciate any help.. 
   
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Subject Re: South Africa Projected Coordinate System 
Author Melita Kennedy 
Date Oct 26, 2009 
Message The South African 'Lo' systems are south-orientated. That is, the positive axes are south and west, rather than east/north. Several people have told me that you define the coordinate system to match the given parameter values, except for the scale factor. Make it negative and that will allow the 'Lo' data to display properly in ArcMap.

You'll have to figure out which zone to use. EPSG Geodetic Parameter Dataset (http://www.epsg-registry.org) has that information. The data could also be on the Cape or Hartebeesthoek94 geographic coordinate systems (datum). Both of those are supported, so when you define your new projected coordinate system, pick the appropriate GCS to base it on.

Melita 
  Melita Kennedy
ESRI Product Specialist 
   
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Subject Re: South Africa Projected Coordinate System 
Author mohammed nazzal 
Date Oct 27, 2009 
Message Thank you for your input..

Here is what I did..

I followed the link to www.epsg-registry.org
I was able to locate the "South African Survey Grid zone 27" with code no. : 17527.
This is exactly what I need since it covers Lesotho (the kingdom of Lesotho which is fully surrounded by South Africa.

I was also able to extract a report from the site for this coordinate system (Please find the report attached). It lists the parameters for defining this system.

The problem is: when I'm defining the new projected system in ArcCatalog, I'm not able to insert all the listed parameters. In addition, I'm not sure what central meridian value to use (I'm assuming 27, but not sure)..
For the geographic system to base the projection on, I selected the WGS84.

I'm attaching couple of images showing the properties of the projected system I'm trying to define..

Please help me finalise this correctly.. Thanks in advance.. 
  Geographic Coordinate System Selection.jpg (opens in new window)
Projected Coordinate System Properties.jpg (opens in new window)
South Africa Survey Grid Lo27.mht (opens in new window)
 
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Subject Re: South Africa Projected Coordinate System 
Author mohammed nazzal 
Date Oct 28, 2009 
Message Oops..

Now I know that central meridian and longitude of the origin frequently if not always refer to the same thing...

Thanks for your help...