Overview
This guide explains how to obtain GNSS position information from a Siretta modem and convert the returned latitude and longitude values into Google Maps compatible decimal degree coordinates.
| Part Number | Description |
|---|---|
| ZETA-GEP-LTE4 (EU) | Low Power LTE Cat 4 European Modem with GPIO and GNSS |
| ZETA-G-GPRS | Entry Level GPRS Modem with GNSS (GL) |
In some applications, the user may require the position of a system shown on Google Maps.
This application note shows how this can be done using a Siretta ZETA modem with GNSS capability.
This document shows how to convert Latitude Longitude coordinates into a position that can be displayed directly on Google Maps.
Expected Result
At the end of this guide the modem should be capable of providing GNSS position information that can be converted into Google Maps compatible coordinates.
The GNSS engine in the ZETA modem will show the Latitude/Longitude position in Decimal Minutes format:
ddmm.mmmm
However, Google Maps requires this information in Decimal Degrees format:
dd.dddd
The solution is to convert position information from one format to the other before displaying the location on Google Maps.
The AT command:
AT$GPSACP
returns latitude and longitude information in Decimal Minutes format.
GPSACP latitude is returned as:
ddmm.mmmm
GPSACP longitude is returned as:
dddmm.mmmm
Resources used:
Follow the Initial Modem Setup Guide application note to communicate with the modem using AT commands.
Issue the following AT command:
AT$GPSP=1
to enable the GNSS engine within the modem.
Issue the AT command:
AT$GPSACP
to obtain latitude and longitude information.
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT AT$GPSP=1 AT$GPSACP |
The returned GPSACP response contains the following information:
| Parameter | Value |
|---|---|
| UTC | 103709.000 |
| Latitude | 5123.1355N |
| Longitude | 00058.4350W |
| HDOP | 9.5 |
| Altitude | 96.0 |
| Fix | 3 |
| COG | 303.4 |
| SPKM | 4.5 |
| SPKN | 2.4 |
| Date | 050224 |
| Nsat_GPS | 03 |
| Nsat_GLONASS | 02 |
This position information can easily be converted into Google Maps compatible latitude and longitude readings as shown below.
For latitude:
Strip the degrees component from:
ddmm.mmmm
Which becomes:
variable1 = dd
variable2 = mm.mmmm
variable3 = variable2 / 60
Rejoin the values to create:
dd.dddd
dd.dddd = variable1 + variable3
For example:
Latitude: 5123.1355 (N)
becomes:
Latitude: dd + mm.mmmm
51 + 23.1355
Latitude: dd + dd.dddd
51 + (23.1355 / 60)
Latitude: 51 + 0.38559
Latitude: 51.38559
Latitude: 51.38559
As this is a North coordinate it remains positive.
Important Note
North coordinates are positive values. South coordinates should be represented as negative values.
Longitude information returned by GPSACP uses the format:
dddmm.mmmm
Example:
00058.4350W
Separate the value into:
ddd = 000
mm.mmmm = 58.4350
Perform the conversion:
58.4350 / 60 = 0.9739
Then recombine the values:
Longitude = 000 + 0.9739
Result:
Longitude = 000.9739
Because the coordinate is West, the longitude must be represented as a negative value.
Longitude = -000.9739
Important Note
West coordinates are negative values. East coordinates are positive values.
After conversion, the GPSACP position becomes:
Latitude = 51.38559
Longitude = -000.9739
These coordinates can now be entered directly into Google Maps.
Navigate to:
http://maps.google.com
Enter the converted coordinates into the search box:
51.38559, -000.9739
and press:
Search Maps
The map will display the location of the Siretta office. :contentReference[oaicite:0]
| Parameter | Value |
|---|---|
| Latitude | 51.38559 |
| Longitude | -000.9739 |
| Google Maps Search | 51.38559, -000.9739 |
For direct access to Google Maps, use the URL format below:
http://maps.google.com/maps?q=51.38559+-000.9739
This URL can be generated dynamically within an application and opened directly in a web browser to display the GNSS position. :contentReference[oaicite:1]
| Direction | Coordinate Sign |
|---|---|
| North | Positive Latitude (+) |
| South | Negative Latitude (-) |
| East | Positive Longitude (+) |
| West | Negative Longitude (-) |
| Step | Action |
|---|---|
| 1 | Enable the GNSS receiver using AT$GPSP=1 |
| 2 | Read position information using AT$GPSACP |
| 3 | Extract latitude and longitude values |
| 4 | Separate degrees from minutes |
| 5 | Divide minutes by 60 |
| 6 | Add the result back to the degree component |
| 7 | Apply the correct coordinate sign |
| 8 | Enter coordinates into Google Maps |
Important Note
AT commandAT$GPSACPmay return different parameter values depending on your location, date, time, number of visible satellites and current GNSS fix status.
Expected Result
The modem should now be capable of providing GNSS latitude and longitude information that can be converted into decimal degree coordinates and displayed directly within Google Maps.