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Convert area from decimal degrees to square...   Claire Wates Jul 27, 2004
Re: Convert area from decimal degrees to sq...   ESRI Developer Support Jul 27, 2004
Re: Convert area from decimal degrees to sq...   Claire Wates Aug 02, 2004
Re: Convert area from decimal degrees to sq...   Imtiaz Ahmad Mar 16, 2005
Re: Convert area from decimal degrees to sq...   ESRI Developer Support Mar 16, 2005
Re: Convert area from decimal degrees to sq...   OJ Milano Jul 30, 2007
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Subject Convert area from decimal degrees to square meters 
Author Claire Wates 
Date Jul 27, 2004 
Message Hi,

I have caluclated the area of a polygon using mapobjects. My layer is in decimal degrees and I need to convert the area to square meters. Does anyone know how to do this without having to convert my layer to lat long first.

Thanks in advance,
Claire 
   
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Subject Re: Convert area from decimal degrees to square meters 
Author ESRI Developer Support  
Date Jul 27, 2004 
Message You're at a dead end, and need to back up a step first. There is no known formula that takes an area value in square decimal degrees and returns an area value in square meters. Square degrees varies all over the globe.

You don't need to convert the layer, simply transform the shape. Then take an area measurement of that projected shape.

a. Make a GeoCoordSys that represents your 'decimal degrees' dataset's coordinate system.
b. Make a ProjCoordSys that preserves accurate area measurements at the scale and in the area of the world the polygon resides.
c. Use the ProjCoordSys's Transform method to project the polygon shape.
d. Read the Area property of that projected Polygon.

If you're not using MO, then our recommendation is to transform each vertex of your polygon into a projection that preserves accurate area measurements in your scale and area of the world, then use your calculation to figure out the area of that projected polygon. 
   
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Subject Re: Convert area from decimal degrees to square meters 
Author Claire Wates 
Date Aug 02, 2004 
Message Hi,

Thanks for the help. It works great!

Claire 
   
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Subject Re: Convert area from decimal degrees to square meters 
Author Imtiaz Ahmad 
Date Mar 16, 2005 
Message Hi Claire,

I am also stuck up with the same issue. I am new to MO. Can you please share some code for the same?

Thanks
Imtiaz
 
   
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Subject Re: Convert area from decimal degrees to square meters 
Author ESRI Developer Support  
Date Mar 16, 2005 
Message Here is an example: 
 
Dim gcs As New MapObjects2.GeoCoordSys
Dim pcs As New MapObjects2.ProCoordSys
Dim polyDegrees As MapObjects2.Polygon
Dim polyMeters As MapObjects2.Polygon

Set polyDegrees = 'your unprojected polygon in decimal degrees
gcs.Type = '**A
pcs.Type = '**B
Set polyMeters = pcs.Transform(gcs, polyDegrees)

...where:

**A = Geographic coordinate system constant for
your unprojected data.

**B = Projected coordinate system constant which
preserves accurate area measurements at the scale 
and area of the world your data represents.

More info:

The optional third argument to the transform 
method is a densification tolerance, helpful with 
lines and polygons to ensure that long straight 
segments between vertices are broken up into new 
vertices so that the transformed shape is as 
accurate as you need it to be.

The optional fourth argument to the Transform 
method is required if the 'from' and 'to' shapes 
are using a different geodetic datum.
 
   
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Subject Re: Convert area from decimal degrees to square meters 
Author OJ Milano 
Date Jul 30, 2007 
Message Not knowing where I am on in the US when I make this calulation how do I come up with B