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# External resources

teaching:m_r:excersize:gnss

# Absolute Positioning

## Excersize Description

### Materials

1. 3 GNSS receivers, set to work with the Hohenheim Reference station. With all cables and antennas.
1. 1 with GNSS - link to a configuration or manual on how to configure the receivers
2. 1 with DGNSS
3. 1 with RTK-GNSS
2. 1 Switch - with 7,5 Voltage regulator.
3. 1 power source - Battery
4. 1 custom powercable.
5. 1 Platform: Armadillo Scout, Gator or the wooden cart from Frau Hadam in the woodworkshop.
6. Wooden Antennamount, with screws.

### Setup

Picture is on the way

## Datalogger

Claes Jaeger-Hansen has written a custom datalogger for the excersize. For Manual, description, executable and sourcecode follow the link

## Help and Hints

Here you can find help and hint to solve the assignment. Not everything is a wlakthrough, so you will have to think a it for yoourself!

### NMEA

All strings in the logs are NMEA-strings. We use two of them in this excersize

GGA
GSA
$GPGGA,080204.00,4842.71680369,N,00912.29472053,E,4,09,1.0,438.255,M,0.000,M,0.0,0000*74$GPGSA,A,3,2,13,23,10,5,8,7,16,4,,,,1.9,1.0,1.6*05

Here are the description of NMEA-string

#### GLONASS/GPS

You can tell the difference between GLONASS and GPS positions from the first 2 letters in the string if it is

$GPGGA the position is from GPS. If it is $GLGGA

the position is from GLONASS

#### Data Format

##### Symbols for degrees, minutes and seconds:
 ° Degrees ' Minutes “ Seconds
##### The three common formats:
 DDD° MM' SS.S” Degrees, Minutes and Seconds DDD° MM.MMM' Degrees and Decimal Minutes DDD.DDDDD° Decimal Degrees
##### Degrees, Minutes and Seconds

DDD° MM' SS.S”
32° 18' 23.1” N 122° 36' 52.5” W

This is the most common format used to mark maps. It's also the most cumbersome to work with. It's a lot like telling time…

There are sixty seconds in a minute (60” = 1') and
There are sixty minutes in a degree (60' = 1°).

Keeping in mind a few easy conversions between seconds and decimal minutes will help when working with maps that use degrees, minutes and seconds.

15 seconds is one quarter of a minute or 0.25 minutes
30 seconds is one half of a minute or 0.5 minutes
45 seconds is three quarters of a minute or 0.75 minutes

##### Degrees and Decimal Minutes

DDD° MM.MMM'
32° 18.385' N 122° 36.875' W

This is the format most commonly used when working with electronic navigation equipment.

##### Decimal Degrees

DDD.DDDDD°
32.30642° N 122.61458° W
or +32.30642, -122.61458

This is the format you'll find most computer based mapping systems displaying. The coordinates are stored internally in a floating point data type, and no additional work is required to print them as a floating point number.

Often the N-S and E-W designators are omitted. Positive values of latitude are north of the equator, negative values to the south. Watch the sign on the longitude, most programs use negative values for west longitude, but a few are opposite. This saves a lazy western hemisphere programmer from having to type in a minus sign before most of their longitude values.

##### Which format should you use?

First off, if you are working with other people who have agreed upon a format to use, then you should probably use that format.

Next, you will want to look at the maps, lists of coordinates, and any software you may be using. If you can find a consistent format among them, your work will be easier.

You can set your GNSS to display any one of these three formats. Locations can be entered into the GNSS with the selected format, and then by switching the display format setting, viewed in a different format.

### Convert from WGS84-"Degrees and Decimal Minutes" to "Decimal Degree"

Format in WGS84 Converted to decimal degrees
latitude longitude latitude longitude
4842,716607 912,293844 48,711943469,2048974

#### Programming Example

This function is in awk, but can be converted to other languages

function nmea2dd(nmeacoord){
dn=int(nmeacoord/100);
return dn+((nmeacoord-(dn*100.0))/60)
}