Specify overview IFD subfile type and IFD order#14
Open
jleben wants to merge 1 commit intocogeotiff:masterfrom
Open
Specify overview IFD subfile type and IFD order#14jleben wants to merge 1 commit intocogeotiff:masterfrom
jleben wants to merge 1 commit intocogeotiff:masterfrom
Conversation
rouault
reviewed
Nov 29, 2022
|
|
||
| The IFDs shall be linked by the pointers (the offset of the first IFD in the file header and the offset of the next IFD in each IFD) so that the full resolution image is first, followed by the overviews. | ||
|
|
||
| Each IFD representing an overview shall have the tag NewSubfileType (254) with a value of 1, indicating the "reduced resolution image" subfile type. |
Collaborator
There was a problem hiding this comment.
IFDs representing a mask should have value 4
IFDs representing the overview of a mask should have value 5
Author
There was a problem hiding this comment.
Thanks, I'll study this suggestion and update the pull request.
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
In order to recognize overviews as such, GDAL needs overview IFDs to have the NewSubfileType tag equal to 1, and that overview IFDs follow the full resolution image according to the order given by the pointers. This is also the minimal requirement that any COG processing software would need in order to identify overviews as such and to associate them with the full resolution image.
This pull request formalizes the above requirements.
In addition, this pull request changes the word "structure" to "layout" to emphasize the distinction between the layout of data in the file versus the logical order of IFDs given by the pointers.