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Calculate inverse

Upgrade your surveying experience with coding, linework, background maps, localization, Inverse & Traverse tools

This guide explains how to use the Inverse tool in Emlid Flow and Emlid Flow 360 to calculate coordinate geometry data such as area, distance, azimuth, and more for known points.


The Inverse tool in Emlid Flow and Emlid Flow 360 allows you to calculate geometry data for existing points. The tool can assist you in such projects as planning civil or utility engineering works and monitoring construction progress.

The software calculates the following values based on the number of input points:

When you select two and more points:

  • Direction (True North azimuth, Grid North azimuth)
  • Slope distance (Slope Ground distance, Slope Grid distance)
  • 2D distance (2D Ground distance, 2D Grid distance)
  • Height difference
  • Grade
  • Delta East (for points in a local CS only)
  • Delta North (for points in a local CS only)

When you select three and more points:

  • Slope distance (Slope Ground distance, Slope Grid distance)
  • 2D distance (2D Ground distance, 2D Grid distance)
  • Area
  • Slope perimeter
  • 2D perimeter

Depending on the coordinate system (CS) used in your project, different distance and azimuth types are used in the calculations:

CS typeDistance typeAzimuth type
Global CSGround distanceTrue North azimuth
Local CSGrid distanceGrid North azimuth

See our Introduction to coordinate systems guide to learn more about distance and azimuth types in different CSs.


When calculating area in a local coordinate system, the software applies a variation of the Shoelace formula, which approximates the area using trapezoids:

Area in a global coordinate system can be calculated for ellipsoid (on the ellipsoid surface) or ground (at the mean ground elevation). We use the method described in section 6 of Algorithms for geodesics by C. F. F. Karney (2013).


To apply the Inverse tool in the Emlid Flow app, follow these steps:

  1. Open the project in Emlid Flow.

  2. Tap the tools button at the bottom left corner of the screen.

  3. Tap Inverse.

  4. Select the points you want to calculate the inverse for from the map or Objects list.


    In Emlid Flow & Emlid Flow 360 you can also find the point-to-point, line, and closed line information for each line. To see this information, just tap on the line.

  5. Click Review to see the calculated results. To calculate results for more than two points, use the arrow buttons to switch to a different set of two points.


    The displayed results will be different depending on the selected points. If you select 2 points, you'll see the point-to-point calculations. If you select 3 points, you'll also see the calculations on the area, slope perimeter, etc.


    You can only use Closed line and Line for geometry measurements. It is not possible to import or export them as geometrical figures.


    You can change the order of the points in the Inverse section by dragging and dropping them. To delete a point, tap the delete button.

  6. To exit the Inverse calculation mode, tap the close button in the upper-right corner.

Further reading