Exif GPS directory and descriptor updates

[nagix]

GPSDirectory

• Add TAG_H_POSITIONING_ERROR (0x001F), which was added in the Exif 2.3 specification

GPSDescriptor

• Add a description for TAG_DOP providing a decimal version of rational numbers
• Add a description for TAG_SPEED providing a decimal version of rational numbers with unit
• Add a description for TAG_DEST_LATITUDE providing a DMS representation of rational numbers
• Add a description for TAG_DEST_LONGITUDE providing a DMS representation of rational numbers
• Add a description for TAG_DEST_DISTANCE providing a decimal version of rational numbers with unit
• Add a description for TAG_PROCESSING_METHOD and TAG_AREA_INFORMATION providing a string representation using the character code stored in the first 8 bytes of the byte array
• Add a description for TAG_H_POSITIONING_ERROR providing a decimal version of rational numbers with unit

[drewnoakes]

Fantastic, as always :)

[nagix]

I borrowed text decoding code from ExifDescriptorBase.getUserCommentDescription() to implement a descriptor for TAG_PROCESSING_METHOD and TAG_AREA_INFORMATION, but should we add a new common method in TagDescriptor and make them use it?

[drewnoakes]

Yes, that method looks complicated enough that it should be extracted into TagDescriptor and reused.

[nagix]

Ok, I created #334 for that.