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I use Convexhull tool in QGIS and there are result value :

AREA = 0.0017494390 PERIMETER = 0.1725495172

I thought the result was strange. So, I took a rough estimate of the points through the services provided by other websites and picked out the results.

Other site result : Area = 17220976.88 m^2 PERIMETER = 17030.657 m

Area value is a difference of 10^10 Perimeter value is a difference of 10^5..

I use "EPSG:4166 - Korean 1995" CRS and I also change project properties for units of distance, area. but, there are not any change.

So, I want to know what convex hull units are in QGIS and how to set other setting for ideal value.

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The unit of EPSG:4166 - Korean 1995 CRS is decimal degree. You need to change the projection of your data to a CRS that uses meter unit. For example, you can use WGS 84 / UTM Zone ## projection with the correct zone number ## in which your data is located in.

The workflow is like this:

  • Change the projection of your data to a WGS 84 / UTM Zone ## with correct Zone number
  • Use the output data from the first step to add new fields for area and perimeter, and calculate both area and perimeter.

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