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.

Overview

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
Direction (azimuth) of a line AB, or from point A to B, is a horizontal angle in degrees, measured at point A clockwise between the direction to the north and the direction to point B.
(
True North azimuth
True North azimuth is the angle ranging from 0 to 360 degrees measured clockwise between True North and the direction to a point of interest.
,
Grid North azimuth
Grid North azimuth is the angle measured clockwise between a line parallel to the central meridian, and the direction to a point of interest (a straight line between two points on the projection flat plane).
)
Slope distance
Slope distance from point A to point B is the length of the straight line AB, measured along the slope, taking the height difference between the points into account.
(
Slope Ground distance
Ground distance is the distance measured on the actual surface of the Earth, taking the mean elevation of the measured points into account.
,
Slope Grid distance
Grid distance is the distance measured on the projection flat plane.
)
2D distance (
2D Ground distance
2D Ground distance between points A and B is the length of the shortest AB line on the surface of the ellipsoid.
,
2D Grid distance
2D Grid distance between points A and B is the length of the straight line AB on a flat plane.
)
Height difference
Grade
Grade of a line is the measure of its steepness, with larger values standing for steeper slopes and 0% indicating a horizontal line.
Delta East
Delta E/N between points A and B is the difference in their coordinates along the corresponding Easting and Northing axes.
(for points in a local CS only)
Delta North
Delta E/N between points A and B is the difference in their coordinates along the corresponding Easting and Northing axes.
(for points in a local CS only)

When you select three and more points:

Slope distance
Slope distance from point A to point B is the length of the straight line AB, measured along the slope, taking the height difference between the points into account.
(
Slope Ground distance
Ground distance is the distance measured on the actual surface of the Earth, taking the mean elevation of the measured points into account.
,
Slope Grid distance
Grid distance is the distance measured on the projection flat plane.
)
2D distance (
2D Ground distance
2D Ground distance between points A and B is the length of the shortest AB line on the surface of the ellipsoid.
,
2D Grid distance
2D Grid distance between points A and B is the length of the straight line AB on a flat plane.
)
Area
Area of an object is the total amount of space enclosed by its shape on flat surface.
Slope perimeter
Slope perimeter of an enclosed object is the sum of slope distances of its sides with the height difference consideration.
2D perimeter
2D perimeter of an enclosed object is the sum of 2D distances of its sides without the height difference consideration.

Depending on the

coordinate system

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

CS type	Distance type	Azimuth type
Global CS	Ground distance Ground distance is the distance measured on the actual surface of the Earth, taking the mean elevation of the measured points into account.	True North azimuth True North azimuth is the angle ranging from 0 to 360 degrees measured clockwise between True North and the direction to a point of interest.
Local CS	Grid distance Grid distance is the distance measured on the projection flat plane.	Grid North azimuth Grid North azimuth is the angle measured clockwise between a line parallel to the central meridian, and the direction to a point of interest (a straight line between two points on the projection flat plane).

tip

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

note

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).

Workflow

Emlid Flow
Emlid Flow 360

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

Open the project in Emlid Flow.
Tap the tools button at the bottom left corner of the screen.
Tap Inverse.
Select the points you want to calculate the inverse for from the map or Objects list.

tip
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.
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.

note
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.

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

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

Overview​

Workflow​

Further reading​

Overview

Workflow

Further reading