WA8LMF Mirror of WB4APR Website - 21 July 2008
Automatic Picture Relay Network
Bob Bruninga, WB4APR@amsat.org
APRN is a concept that should revolutionize the use of amateur radio in support of emergencies, special events and public service. It allows mobile, portable and handheld operators to send back live images from the field for real-time review anywhere, using ANY radio! Prior to APRN, images could be sent from one SSTV station to another, but since fewer than a fraction of 1% of ham operators had SSTV capability, there was no way to get the image from the receiver to the person, VIP, or agency that needed it.
All of that has changed with the advent of SIX powerful technologies that have coalessed in the last few years:
KEN-CAM (Kenwood VC-H1): Although SSTV has been around for 30 years or more, it has always been a relatively boring exchange of pre-captured images between hamshacks. Recently, Camera interfaces have existed, but it still required a PC or other large appliance to convert the image to SSTV. The arrival of the Kenwood KEN-CAM (VC-H1) in 1997, completely changed the playing field, since the entire system fits in a shirt pocket or the palm of your hand and can be used anywhere. This combined with the public's general acceptance of still-frame video over the internet totally embraces a complete paradigm shift to a totally new real-time in-the-field imaging capability.
APRS HT (Kenwood TH-D7) The final key to the automation of the WEB PAGE interface for APRN was the imminent introduction by Kenwood of the TH-D7 APRS packet walkie-talkie. . This radio, without a computer, or any external components, allows a user to not only Capture the picture with his handheld Ken-Cam (VC-H1), but also then transmit a machine readable single packet identifier that includes the CALLSIGN, LOCATION, TIME, TITLE, Direction and field of view of the image!
IMAGE IDENTIFICATION: The keypad on the Kenwood TH-D7 can be used for entering the necessary alphanumerics and the built-in TNC then transmits it. . If a GPS is plugged into the radio as well, then the LAT/LONG of the station is also automatically included! Thus you can transmit the WHO, WHAT WHEN, and WHERE needed for full automation of the WEB page for cataloging and indexing real-time images from multiple remote users.
POSITION REPORTING: The existing APRS network linked worldwide by Steve Dimse's APRServe system serves as the GEO-POSITION locator system for APRN to show WHERE the images were taken in real time.
APRN NETWORK The APRN network is not really a network at all. It is only the establishment of designated frequencies in cities everywhere for Ken-Cam operators to uplink their images to the nearest APRN node which then hosts the images as WEB pages. These local networks can be as simple or complex as needed to provide the mobile converage needed. A few examples follow:
FREQUENCIES: Frequencies are a local issue only. Typically, only one frequency is needed and it can be shared with other applications. ALso, since only mobiles or remotes uplink on the channel in simplex to the APRN receiver, any simplex frequency can be used. There is no need for the APRN site to transmit anything on the channel back to the user other than a brief 1 second acknowledgment. Thus it is consistent with simplex shared use.
APRN FORMAT: The value added to SSTV by the APRS identification packet cannot be over emphasized. Without this human readable data, the SSTV image is just an un-identifiable picture. But with an APRS packet identifier, then the picture becomes so much more valuable. . All of the following information is added to the picture with APRS:
APRS SSTV SYMBOL: Since 1997, APRS has a well defined SSTV symbol "/T". . Any station sending a packet as an SSTV image identifier packet, should use this symbol. All of the above fields are self explanitory except for the DIRECTION and FOV. . It is proposed that for this symbol and this application, that the normal CSE/SPD field of the packet be interpreted not as CSE/SPD but as DIR/FOV. . The use of CSE to indicate the direction the camera is pointing is relatively straight forward. But we can use the SPD field to include the width of the FOV in degrees. . There is no loss of significance to the actual CSE and SPD fields, because if this packet is being used to identify a picture, then CSE and SPD are meaningless in this context. But DIR and FOV are very valuable. . Imagine an APRS map that can not only show the location that an image was taken, but also the camera direction and FOV with an overlayed WEDGE!
GLOBAL APRN ACCESS: All of the above items of information associated with the image are transmitted in the initial packet by the originator. This is what any APRS packet station wouild capture if he were monitoring the original packet. . But the real value-added by the local APRN-Receiving node is the archiving of that image and that data for on-line retrieval by anyone, anywhere via the internet. In that regard, the APRN takes the originators original APRS packet, parses out the information and after archiving the data, it then re-formats the data into a new standard APRN packet onto the APRS-IS but with the addition of "//URL..." on the end. This "//URL..." is the full URL of the now-saved image. . THis packet being injected into the APRS global Internet System (APRS-IS) is now available anywhere in the world. . The following OBJECT format is suggested:
Where the original image is number nnn originated by WB4APR, and it was received by the KB2SCS APRN node at DDHHMMz and injected into the APRS-IS as an object with these fields:
That makes the image then available worldwide within the APRS-IS system by the simple reference to the APRS object "WB4APRnnn" and then its URL.
de WB4APR, Bob
NOTE! These pages are NOT yet automatic. The purpose of this APRN web page is top show what we COULD do with SSTV. WA8LMF Mirror of WB4APR Website - 21 July 2008