Object and Item Reports¶
Objects and ItemsAny APRS station can manually report the position of an APRS entity (e.g. another station or a weather phenomenon). This is intended for situations where the entity is not capable of reporting its own position.
APRS provides two types of report to support this:
-
- Object Reports
- Item Reports
Object Reports specify an Object’s position, can have an optional timestamp, and can include course/speed information or other Extended Data. Object Reports are intended primarily for plotting the positions of moving objects (e.g. spacecraft, storms, marathon runners without trackers).
Item Reports specify an Item’s position, but cannot have a timestamp. While Item reports may also include course/speed or other Extended Data, they are really intended for inanimate things that are occasionally posted on a map (e.g. marathon checkpoints or first-aid posts). Otherwise they are handled in the same way as Object Reports.
Objects are distinguished from each other by having different Object names. Similarly, Items are distinguished from each other by having different Item names.
Implementation Recommendation: When an APRS Object/Item is displayed on the screen, the callsign of the station sending the report should be associated with the Object/Item.
Replacing an Object / Item¶
A fundamental precept of APRS is that any station may take over the reporting responsibility for an APRS Object or Item, by simply transmitting a new report with the same Object/Item name.
The replacement report may specify the existing location or a new location.
The original station will cease transmitting an Object/Item Report when it sees an incoming report with the same name from another station.
Killing an Object / Item¶
To kill an Object/Item, a station transmits a new Object/Item Report, with a “kill” character following the Object/Item name.
Implementation Recommendation: When an Object/Item is killed it should be removed from display on the screen. However, the data associated with the Object/Item should be retained internally in case it is needed later.
Additional Amplifying Comments about Objects
Object Report Format¶
An Object Report has a fixed 9-character Object name field, which may consist of any printable ASCII characters, including embedded spaces. Trailing spaces are used to make the field 9 characters wide. These are not part of the name. Object names are case-sensitive.
The ; is the APRS Data Type Identifier for an Object Report, and a * or _
separates the Object name from the rest of the report:
* indicates a live Object.
_ indicates a killed Object.
- The position may be in lat/long or compressed lat/long format, and the report may also contain Extended Data. Compressed Objects arenot recommended for use on RF due to incompatibilities. For 1 foot precision, use the !DAO! format.
An Object always has a timestamp.
The Comment field may contain any appropriate APRS data (see the Comment Field section in Chapter 5: APRS Data in the AX.25 Information Field).
Why is the Comment field restricted to 36 or 43 characters? Chapter 3 states that the Information part can be up to 256 characters.
APRS 1.1: The compressed version is not recommended.
| Object Report Format — with Lat/Long position | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| ; | Object Name | * or _ | Time DHM / HMS | Lat | Sym Table ID | Long | Symbol Code | Course/Speed | Comment (max 36 chars with Data Extension, or 43 without) |
| Power/Height/Gain/Dir | |||||||||
| Radio Range | |||||||||
| DF Signal Strength | |||||||||
| Area Object | |||||||||
| 1 | 9 | 1 | 7 | 8 | 1 | 9 | 1 | 7 | 0-36/43 |
| Examples ;LEADER˽˽˽*092345z4903.50N/07201.75W>088/036 A live Object. At 2345 hours zulu on the 9th of the month, the “Leader” was in the car at 49°3'30"N/72°1'45"W, heading 88 deg at 36 knots. ;LEADER˽˽˽_092345z4903.50N/07201.75W>088/036 The same Object, now killed. |
Bytes:
| Object Report Format — with Compressed Lat/Long position - not recommended. | |||||
|---|---|---|---|---|---|
| ; | Object Name | * or _ | Time DHM / HMS | Compressed Position Data /YYYYXXXX$csT | Comment |
| 1 | 9 | 1 | 7 | 13 | 43 |
| Example ;LEADER˽˽˽*092345z/5L!!<*e7>7P[ The “Leader” was in the car at 49°30'00"N/ 72°45'00"W, heading 88 deg at 36.2 knots. |
Bytes:
Item Report Format (not recommended)¶
An Item Report has a variable-length Item name, 3–9 characters long. The name may consist of any printable ASCII characters, including embedded space, except ! or _ because they are the field terminator.
Item names are case-sensitive.
Note that the name field is variable length, rather than fixed, as with objects.
The ) is the APRS Data Type Identifier for an Item Report, and a ! or _
separates the Item name from the rest of the report:
! indicates a live Item.
_ is the Item “kill” character.
The position may be in lat/long or compressed lat/long format. There is no provision for a timestamp. The report may also contain Extended Data.
The Comment field may contain any appropriate APRS data (see the Comment Field section in Chapter 5: APRS Data in the AX.25 Information Field).
APRS 1.1: The Item Format is not recommended on RF due to incompatibilities.
Bytes:
| Item Report Format — with Lat/Long position - Not Recommended | ||||||||
|---|---|---|---|---|---|---|---|---|
| ) | Item Name | ! or _ | Lat | Sym Table ID | Long | Symbol Code | Course/Speed | Comment (max 36 chars with Data Extension, or 43 without) |
| Power/Height/Gain/Dir | ||||||||
| Radio Range | ||||||||
| DF Signal Strength | ||||||||
| Area Object | ||||||||
| 1 | 3-9 | 1 | 8 | 1 | 9 | 1 | 7 | 0-36/43 |
| Examples )AID#2!4903.50N/07201.75WA First Aid Station #2 is at 49°3'30"N/72°1'45"W. (/A is the symbol for Aid Station). )G/WB4APR!53˽˽.˽˽N**002˽˽.˽˽Wd A rare DX station “somewhere in England”. (\d is the symbol for DX Spot). )AID˽#2_4903.50N/07201.75WA** The First Aid Station has closed down. |
Bytes:
| Item Report Format — with Compressed Lat/Long position - Not Recommended | ||||
|---|---|---|---|---|
| ) | Item Name | ! or _ | Compressed Position Data /YYYYXXXX$csT | Comment |
| 1 | 3-9 | 1 | 13 | 43 |
| Example )MOBIL!**5L!!<*e79sT Mobil Gas Station is at 49°30'00"N/72°45'00"W. (\9** is the symbol for Gas Station). |
Area ObjectsUsing the \l symbol (i.e. the lower-case letter “L” symbol from the Alternate Symbol Table) it is possible to define circle, line, ellipse, triangle and box objects in all colors, either open or filled in, any size from 60 feet to 100 miles.
These Objects are useful for real-time events such as for a search-and-rescue, or adding a special road or route for a special event.
The Object format is specified as a 7-character APRS Data Extension
Tyy/Cxx immediately following the l Symbol Code. For example:
;OBJECT˽˽˽*ddmm.hhN**dddmm.hhW l** Tyy/Cxx
where:
T is the type of object shape.
/C is the color of the object.
yy is the square root of (the latitude offset in degrees / 1500).
xx is the square root of (the longitude offset in degrees / 1500).
On the receiving end:
offset_in_degrees = (offset_in_packet^2) / 1500
NOTE: This specification originally had a scaling factor of 100. http://www.aprs.org/aprs11/areaobjects.txt contains the correction to make it 1500. All of the modern applications checked use 1500.
The object type and color codes are as follows:
| T | Object Type |
|---|---|
| 0 | Open circle |
| 1 | Line (offset: down/right) |
| 2 | Open ellipse |
| 3 | Open triangle |
| 4 | Open box |
| 5 | Color-filled circle |
| 6 | Line (offset: down/left) |
| 7 | Color-filled ellipse |
| 8 | Color-filled triangle |
| 9 | Color-filled box |
| /C | Object Color | Intensity |
|---|---|---|
| /0 | Black | High |
| /1 | Blue | High |
| /2 | Green | High |
| /3 | Cyan | High |
| /4 | Red | High |
| /5 | Violet | High |
| /6 | Yellow | High |
| /7 | Gray | High |
| /8 | Black | Low |
| /9 | Blue | Low |
| 10 | Green | Low |
| 11 | Cyan | Low |
| 12 | Red | Low |
| 13 | Violet | Low |
| 14 | Yellow | Low |
| 15 | Gray | Low |
- Triangles are always isosceles triangles, oriented vertically and the points of reference are the top APEX and the lower right corner.
- Circles are defined by a square box referenced by the upper left corner and the center.
- Lines are referenced to the upper end.
The 'offset reference' position of the object is the upper left corner
of the object and the offsets are the distance from the lower right
corner (or center of a circle) back to this "offset reference" position.
(An exception is the special case of a type-6 line which is drawn down
and to the left).
Here are some examples of Object Position Reports. The latitude and longitude offsets are each 4 minutes = 4/60 degree = 100/1500 of a degree), so
yy = xx = √100 = 10.
;SEARCH˽˽˽*092345z4903.50N**07201.75W l 710/310**
A high intensity cyan filled ellipse, yy=10, xx=10
;SEARCH˽˽˽*092345z4903.50N**07201.75W l 8101310**
A low intensity violet filled triangle, yy=10, xx=10
Further, with the line option (Type 1 and Type 6) it is possible to specify a “corridor” either side of the central line. The width of the corridor (in miles) either side of the line is specified in the comment text, enclosed by {}.
For example:
;FLIGHTPTH*4903.50N**07201.75W l 610/310{100}**
A high intensity cyan line, with a 100-mile corridor either side
Note: The color fill option should be used with care, since a color-filled object will obscure information displayed underneath it.
Signpost Objects/Items¶
Signpost Objects/Items (with the symbol \m) display as a yellow box with a 1–3-character overlay on them. The overlay is specified by enclosing the 1–3 characters in braces in the comment field. Thus a signpost with {55} would appear as a sign with 55 on it.
For example:
)I91˽3N!4903.50N**07201.75Wm{55}**
This was originally designed for posting the speed of traffic past speed measuring devices, but can be used for any purpose.
Implementation Recommendation: Signposts should not display any callsign or name, and to avoid clutter should only be displayed at close range.
.
Obsolete Object Format¶
Some stations transmit Object reports without the ; APRS Data Type Identifier. This format is obsolete. Some software may still decode such data as an Object, but it should now be interpreted as a Status Report.