Make repeated WGS84-Mercator conversion stable #897
Merged
Conversation
This file contains 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
Includes test which passes with these changes in place. Also added and updated Javadoc. This is a more minimal changeset than originally proposed, to facilitate review and contain risk from changing heavily used math functions.
abyrd
commented
Oct 19, 2023
Comment on lines
+139
to
+141
| // Find width and height in whole pixels, handling the case where the right envelope edge is on a pixel edge. | ||
| int height = (int) Math.ceil(latToFractionalPixel(wgsEnvelope.getMinY(), zoom) - north); | ||
| int width = (int) Math.ceil(lonToFractionalPixel(wgsEnvelope.getMaxX(), zoom) - west); |
There was a problem hiding this comment.
Note that this is a key part of the PR, using ceil() to handle the case where the projected value already lies exactly on a pixel boundary.
This was referenced Oct 19, 2023
ansoncfit
approved these changes
Oct 20, 2023
|
A corresponding or related UI PR is https://github.com/conveyal/ui/pull/1985, where I made some comments about coordinating behavior between the two sides. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
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Outdated suggestions cannot be applied.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.
This PR supersedes #892, which has been split into multiple PRs. This is a more minimal changeset than originally proposed, to facilitate review and contain any risk from changing heavily used math functions.
As recently discussed: regional request bounds are specified in WGS84 coordinates, which are converted to web Mercator extents when regional tasks are processed. Repeating a regional analysis with the same bounds as an existing one requires the the UI to look at the web Mercator bounds of an existing analysis, then convert them to WGS84 to create the new regional analysis request. This creates a feedback loop between WGS84 and web Mercator where WGS84 bounding boxes lie exactly on the edges of Mercator pixels, creating a literal edge case for the function
WebMercatorExtents#forWgsEnvelopeandpopulateTask.This PR revises the way web Mercator extents are created to handle this edge case. This change is reinforced with additional factory methods that should handle any numerical instability or lack of precision in the repeated conversions.
The eventual real fix for this is #893.
This PR includes a test of repeated conversions, which fails without these changes and passes with these changes.
Javadoc was also added and updated.