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FME Desktop 2014

Why do the values I get with FME AreaCalculator and LengthCalculator differ from the values displayed in MapInfo? Can I get the same values as calculated by MapInfo Area() and ObjectLen() functions using FME?

Comparing area/length calculated with MapInfo to area/length calculated with FME is quite often confusing. You do get some difference in numbers. This is why: MapInfo uses either
**Cartesian **or **Spherical **method to calculate areas/distances (**Spherical **is used by default when possible), while FME always uses **Cartesian **method.

This is how both methods are described in MapInfo Help:

**Spherical**- The Spherical calculations measure distance according to the curved surface of the Earth.**Spherical**is the default. The data is first converted to Latitude/Longitude and then a calculation is produced. Lat/Long data will always use spherical calculations.**Cartesian**- The Cartesian method performs calculations on data projected onto a flat plane. Cartesian coordinates (x,y) define the position of a point in two-dimensional space by its perpendicular projection onto two axes which are at right angles to each other. Long/Lat projections cannot use Cartesian calculations.

To switch from Spherical calculation to Cartesian in MapInfo map window, please, select Map > Options.. and change the setting in Distance/Area Using GroupBox.

If you use a MapInfo function to calculate an object area in MapInfo, you have three options: you can use either Area(), or SphericalArea(), or CartesianArea() function.

- If the table is Longitude\Latitude based, a SphericalArea() or Area() function can be used. If CartesianArea() is used on Longitdue\Latitude tables, a value of -1 will be returned.
- If the table is Non-Earth based, CartesianArea() and Area() functions can be used. If SphericalArea() is used on Non-Earth tables, a value of -1 will be returned.
- Any other projection or projected coordinate system tables other than Longitude\Latitude or Non-Earth (e.g.: UTM, Albers, Gauss-Kruger, Robinson, State Plane, etc.) can use all three functions of SphericalArea(), CartesianArea() or Area() to calculate this value in a column.

NB: Area() will use the method set in Map > Options... > Distance/Area Using.

The same applies to object length calculation using MapInfo functions. The three options in this case are: **ObjectLen()**, **SphericalObjectLen()**, and **CartesianObjectLen()**.

If you open your data in MapInfo, set Cartesian for distance/area calculation in map options, and check Cartesian area or length of an object, you will get exactly the same value as calculated by FME.

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Coordinate Systems and Measurements with the Reprojector

Calculating Area, Perimeter, and Lengths

Distance Measurements with the LengthCalculator

Shortest Route Calculations with the ShortestPathFinder

Projection Definition and Coordinate Transformation

How does FME interact with ESRI coordinate systems?

Point in Polygon Calculations with the PointOnAreaOverlayer

Using the CoordinateSystemSetter to Tag Data with the Correct Coordinate System

How to convert MapInfo to Shapefile (MIF/MID to SHP)

Using external coordinate system names with CoordinateSystemDescriptionConverter

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