GPSImgDirection, GPSDestBearing documentation?

[obetz]

Hi all,

where can I find a detailed description of the GPS Tags? I have the "CIPA DC-008-Translation- 2016" but IMO it's somewhat fuzzy.

For example, I wonder what GPSImgDirection and GPSDestBearing are intended to represent.

The docs state that GPSDestBearing is "the bearing to the destination point". But from which position other than the camera position? The camera position comes to mind but...

GPSImgDirection is often used as the direction the camera pointed to, so what might "bearing" be different?

BTW: Should it/they be calculated if GPSDestLongitude/Latitude or GPSLongitude/Latitude are set or modified manually?

The MWG guidance mentions neither direction nor bearing as far as I see.

Could ExifTool do this calculation or is it to be done by the application?

The same might apply to GPSDestDistance. And how is it related to Subject Distance?

After all:

Can it be that these tags are either misleading named or abused? In my imagination, one GPS receiver will be at the camera position but hardly at the target/destination/shown position, and the destination position will be determined by other means than "GPS".

Oliver

[StarGeek]

Yeah, the specs are a bit fuzzy

GPSImgDirection is "Direction of image when captured, values range from 0 to 359.99."

GPSDestBearing is "the bearing to the destination point. The range of values is from 0.00 to 359.99."

Hmmm...  I'd interpret that as GPSDestBearing is the direction of movement, while GPSImgDirection the camera is facing.  For example, if you were traveling North, but looked to the left as you took a picture, then  GPSImgDirection would be 0.0, while GPSDestBearing would be 270.

I think iPhone6+ might capture both these items, so if you know someone with one, you could test it out.

[obetz]

Hmmm...  I'd interpret that as GPSDestBearing is the direction of movement

no, the direction of movement is GPSTrack.

And since the movement doesn't need to be directed to the "destination point", I don't think that bearing is related to the movement but only to the position(s).

It also can't be a relative bearing because GPSDestBearingRef can be only "T" and "M" yet related to "North". A relative bearing doesn't depend on magnetic deviation.

I know Iphone owners but I wouldn't rely on Apple regarding this issue.

Oliver

[Phil Harvey]

The GPSDest tags refer to the direction to the programmed destination point.

- Phil

[StarGeek]

The GPSDest tags refer to the direction to the programmed destination point.

It sounds like searching under GPS Navigation would reveal more info regarding the more obscure tags.  For example Definition of Bearing in GPS Navigation.

[obetz]

Hi Phil,

The GPSDest tags refer to the direction to the programmed destination point.

If I interpret this correctly, you say that GPSDestLongitude/Latitude does not describe the position of the object shown but some coordinates I had set in my GPS device for navigation purposes e.g. the next waypoint I want to go to?

From a (GPS-) technical point of view, that would make sense. My GPS device indeed has waypoints I navigate to and theses waypoints are not the positions of the objects shown. And then also the distinction between heading (to GPSDestLongitude/Latitude, correct?) and GPSImgDirection (where I headed the camera) would be clear.

But MWG Guidlines "5.8.3 Location Shown (GPS Latitude/Longitude)" tell me that GPSDestLongitude/Latitude ("GPS data: Exif GPS (34853:[19-26], 0x8825:[19-26]) [...] can be read directly without any reconciliation being required".

Recommends MWG to use the Exif tags differently than intended by JEITA?

Oliver

[Phil Harvey]

Hi Oliver,

GPSDestLongitude/Latitude does not describe the position of the object shown but some coordinates I had set in my GPS device for navigation purposes e.g. the next waypoint I want to go to?

Exactly.

to GPSDestLongitude/Latitude, correct?

Yes.

But MWG Guidlines "5.8.3 Location Shown (GPS Latitude/Longitude)" tell me that GPSDestLongitude/Latitude ("GPS data: Exif GPS (34853:[19-26], 0x8825:[19-26]) [...] can be read directly without any reconciliation being required".

Recommends MWG to use the Exif tags differently than intended by JEITA?

Right.  I don't know if I had noticed this before, but the MWG is using the GPSDest tags for the "Location Shown".  This is not their original purpose.  (Assuming I am correct about their original purpose, which seems clear to me from my background using GPS for sonar surveys back in the mid 90's -- I always assumed that the EXIF GPS specification was based on the NMEA protocol, so the GPSDest tags should be based on the $GPRMB NMEA sentence.)

- Phil

[obetz]

Hi Phil,

Recommends MWG to use the Exif tags differently than intended by JEITA?

Right.  I don't know if I had noticed this before, but the MWG is using the GPSDest tags for the "Location Shown".  This is not their original purpose.  (Assuming I am correct about their original purpose, which seems clear to me from my background using GPS for sonar surveys back in the mid 90's -- I always assumed that the EXIF GPS specification was based on the NMEA protocol, so the GPSDest tags should be based on the $GPRMB NMEA sentence.)

So the interesting question is what use is "right" or at least safe today even if it differs from the historic idea.

The MWG suggestion is in my opinion much more useful for describing images than some waypoint I had in my navigation system.

And MWG should explain this rededication.

Oliver