Introduction to coordinate systems

Overview

To define the precise location of surveyed objects in the world, you need to set up a

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

(CS) when creating a project.

When choosing a

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

, you should make the decision based on the area you want to work in: for each region, there is a

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

optimized for this specific area. Once you’ve determined in which CS you need the

rover’s

Rover is one of the two GNSS receivers that is used for collecting data in RTK or PPK scenarios. Rover is a moving unit: the surveyor uses rover to record the points, while rover receives the corrections from the static base.

coordinates and which base datum is required, check if you can obtain coordinates of a known point in the same datum.

caution

A mismatch in the CS setup between your

rover

Rover is one of the two GNSS receivers that is used for collecting data in RTK or PPK scenarios. Rover is a moving unit: the surveyor uses rover to record the points, while rover receives the corrections from the static base.

and your

base

Base is one of the receivers that act as a reference station in RTK or PPK scenarios. It is a static unit with the determined coordinates that sends corrections to the moving unit or rover. If the base is set over the known point, it provides absolute accuracy.

or the NTRIP service can result in poor accuracy of survey results.

Setup

You can set up the CS for your project in several ways.

Choose from the library

Emlid Flow and Emlid Flow 360 contain the verified registry of local CSs for specific countries. Every

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

is based on a specific local datum. The datum is projected onto the flat surface using projection. All you need is to find your country in the registry and apply it to your project. The information provided for each country explains which datum should be used for both your

rover

Rover is one of the two GNSS receivers that is used for collecting data in RTK or PPK scenarios. Rover is a moving unit: the surveyor uses rover to record the points, while rover receives the corrections from the static base.

and your base or

NTRIP

The Networked Transport of RTCM via Internet Protocol or NTRIP network is an alternative source of corrections. NTRIP allows your rover to accept corrections over the Internet with no need for the second local receiver acting as a base. A reference station collects data, then sends it to NTRIP caster, where it is retransmitted through the Internet port to the client rover connected via a particular port and authorized.

.

In this case, the apps apply

Grid distance

Grid distance is the distance measured on the projection flat plane.

and

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).

. Grid distance is the distance measured on the projection flat plane. 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).

Below is an example of a local

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

you can use in Emlid Flow & Emlid Flow 360: NAD83(2011) / California zone 56 where NAD83(2011) is a datum, California zone 5—a projection. When setting up a project on your

rover

Rover is one of the two GNSS receivers that is used for collecting data in RTK or PPK scenarios. Rover is a moving unit: the surveyor uses rover to record the points, while rover receives the corrections from the static base.

, pay attention to the note in the Emlid Flow app. It will show you in which datum your base or

NTRIP

The Networked Transport of RTCM via Internet Protocol or NTRIP network is an alternative source of corrections. NTRIP allows your rover to accept corrections over the Internet with no need for the second local receiver acting as a base. A reference station collects data, then sends it to NTRIP caster, where it is retransmitted through the Internet port to the client rover connected via a particular port and authorized.

should be.

Here NAD83(2011) is a datum,
California zone 5—a projection.

Apply global CS

This option is used to get started with the Emlid Flow app and quick tests in the field. As a result, you get geographic coordinates—latitude, longitude, ellipsoid height—in the datum of your base.

In this case, the apps apply

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.

and

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.

. 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 is the angle ranging from 0 to 360 degrees measured clockwise between True North and the direction to a point of interest.

Below is an example of using the Global CS option in Emlid Flow & Emlid Flow 360. If you enter the base coordinates in NAD83(2011) in the Base settings, you’ll get the NAD83(2011) coordinates with the

rover

Rover is one of the two GNSS receivers that is used for collecting data in RTK or PPK scenarios. Rover is a moving unit: the surveyor uses rover to record the points, while rover receives the corrections from the static base.

by default.

Use custom CS

If you know the projection parameters and the required local coordinate system is not supported in Emlid Flow and Emlid Flow 360, you can add your own CS by entering the following parameters:

note

Since not every group of parameters is required for a

coordinate system

Coordinate system is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems.

configuration, you may omit some of them and only use the parameters that you have for your projection.

• Ellipsoid your datum is based on
• Projection type and its parameters
• Transformation type and its parameters
• Geoid model

In this case, the apps apply

Grid distance

Grid distance is the distance measured on the projection flat plane.

and

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).

. Grid distance is the distance measured on the projection flat plane. 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).

Below is the example of a custom CS set up in Emlid Flow.