Key Elements

Here is a shell script to receive APRS packet audio through the microphone input:

 arecord -f S16_LE -c 1 -r 48000 -D hw:CARD=Device,DEV=0 - |sox -t raw -esigned-integer  -b16 -r 48000 - -esigned-integer -b16 -r 22050 -t raw - | multimon-ng -q -v 10 -t raw -A - | python aprs_parser.py  

Here is a shell script to receive APRS packets from a RTL-2832 TV Tuner:

 rtl_fm -f 144.390M -s 22050 - | multimon-ng -q -v 10 -t raw -A - | python aprs_parser.py  

aprs_parser.py is a script I wrote to decode the APRS packets and insert into the PostgreSQL/PostGIS database.  I'll post it when I clean the code up. It uses SQLAlchemy, Geoalchemy2, and aprslib Python modules.

The PostgresSQL/PostGIS database needs to have a geometry column with spatial reference id of 4326 (aka WGS_1984).

Interoperability Conference 2017

Open GIS Server with Raspberry Pi and Radio

Presentation Slides

This was a side project I worked on at night to see if I could run a geographic information system (GIS) that could support both traditional desktop application and modern web mapping applications (server/client). The Raspberry Pi is used to listen for and capture digital data containing location information and insert it into the GIS database.

The goal of this was to get audience members thinking about GIS and how it might be useful or could be applied in the radio/communication community.  

I hope to publish a build log as well as the code I wrote to handle the database insertion.

73,
KE8CRV

GIS Data Sources

Finding sources of GIS data can be frustrating for several reasons:

• Many formats and coordinate systems
• Lack of metadata
• Data has not been updated
• Restrictions that prevent sharing

Here are some useful links and the types of layers that can be found.

State of Michigan
http://gis.michigan.opendata.arcgis.com/

• All Roads
• Boundaries
• Rivers and Lakes
• Imagery
• Elevation Data

Federal Government
https://hifld-dhs-gii.opendata.arcgis.com/

• Hospitals
• FEMA Regions
• Communication Towers

https://nationalmap.gov/ustopo/index.html

• Topo Maps

https://earthexplorer.usgs.gov/

• Imagery
• Historical Imagery
• Elevation

http://www.census.gov/data/data-tools.html

• Population

City or County

Check with the County or City websites for GIS data. 

• Parcel data

Open Street Map
http://wiki.openstreetmap.org/wiki/Downloading_data

• Basemap

Global Administrative Areas
http://gadm.org/

• Basemap:   Lots of data.  May be better off using Natural Earth Data sets instead

Natural Earth Data

http://www.naturalearthdata.com/

• Basemaps

US National Grid (USNG)
http://usngcenter.org/fema-region-5/

UTM Zones
http://earth-info.nga.mil/GandG/coordsys/grids/universal_grid_system.html

American Red Cross National Shelter System (NSS)
https://gis.fema.gov/REST/services/NSS/FEMA_NSS/MapServer

Geocoding
https://geocoding.geo.census.gov/geocoder
https://geoservices.tamu.edu/

What other types of data should be included in an offline GIS?  Let me know in the comments section.

Imagery from US Topo Maps

With a couple command lines, you can convert US Topo Map pdfs into layers that can be used in GIS or to form a basemap that can be used offline.

US Topo 2 Tif  - This PDF is a good resource to have in an offline GIS.

Download the areas of interest from the US GeoPDF Topo Maps.  These are good to have on hand for printing or for loading to mobile apps like Avenza PDF.

The following examples will assume the pdf is called "MN_Grand_Marais_20160511_TM_geo.pdf"

Run the GDAL command:

gdalinfo MN_Grand_Marais_20160511_TM_geo.pdf –mdd LAYERS

This will allow you to see all the layer names.

Then run the GDAL command:

gdal_translate MN_Grand_Marais_20160511_TM_geo.pdf marais_contours.tif \
--config GDAL_PDF_LAYERS "Map_Frame.Terrain.Contours" --config GDAL_PDF_BANDS 3 \
--config GDAL_PDF_DPI 400

You will now have a TIF file that can can be loaded into the open source GIS

There are additional command line options to do compression and other stuff to the outputs.  Check the pdf for more info.

Stack Preview

Here is a preview of the ODroid C2 stack.  Currently the brass standoffs are mounted to a piece of acryllic I got from Menards.  Still need to come up with a with a good case design.  You can imagine how easy this would fit into a Pelican case to provide a temporary mobile GIS server,

Ideas for cases?  Let me know in the comments.

GeoNode and /tmp

I noticed that when you use the web browser to load layers into GeoNode, the data gets stored and uncompressed in /tmp.   This is a problem, since the ODroid C2 has 16GB eMMC.   Fortunately, the C2 can run both eMMC and SD Card storage simultaneous.

I added a 32 GB SD Card to the ODroid C2 that was hosting GeoNode.  Here are the steps to do this:

su root

Use fdisk to list the devices:

fdisk -l

Create new partition with the device id that belongs to the SD Card:

fdisk /dev/mmcblk1

Create new primary partition, use default settings

Format the new partition:

mkfs.ext4 /dev/mmcblk1p1

Automount the new partition by editing  /etc/fstab

Add line:

/dev/mmcblk1p1 /tmp ext4 defaults 0 0

Allow read/write access

chmod 777 /tmp

Reboot and you should see GeoNode start using the new /tmp directory.  You can check by running this command:

df -h

This will also need to be done to accommodate the geonode data directories.  This will be done in a further blog post.

APRS and Laptop Power Cord Interference

One of the great things about the Kenwood TH-D74A is how easy APRS is to use. However I was puzzled for a few days because I could not make it work with my rtl-sdr receiver within my apartment.  It turns out my Lenovo W520 Laptop power cord was causing just enough interference to make the TH-D74 think it was receiving a message all the time preventing the HT from transmitting.

At the time, I was developing a python script to extract location data from APRS packets.  I had my cheap RTL2832 tv tuner plugged into an Odroid C2 on a different monitor and was watching the waterfall with GQRX.  After turning off all other electronics in the house, the spike near 144.390 MHz went away.   Trial and error revealed the problem to be with the laptop power supply.

Hooray!