Bug 366245

Summary:	height value used in globe projection leads to blurred images
Product:	[Applications] marble	Reporter:	Rolf Eike Beer <kde>
Component:	general	Assignee:	marble-bugs
Status:	CONFIRMED ---
Severity:	normal	CC:	rahn
Priority:	NOR
Version:	22.08.2
Target Milestone:	---
Platform:	openSUSE
OS:	Linux
Latest Commit:		Version Fixed In:
Sentry Crash Report:

Description Rolf Eike Beer 2016-07-29 15:26:24 UTC

The height values on bigger zoom levels differs from globe to merkator projection, so the tiles will get scaled and everything on them becomes blurred. On high zoom levels there is no reason to not use the same height value, the globe effect is so small it should be entirely ignored there.

Reproducible: Always

Steps to Reproduce:
1. use a map of something like 40x20 kilometers or anything smaller
2. switch between globe and merkator projections
3. observe that the images get blurred in globe
4. zoom in even more, where the same problem will be visible for any other zoom level

Comment 1 Justin Zobel 2022-10-21 23:59:52 UTC

Thank you for reporting this bug in KDE software. As it has been a while since this issue was reported, can we please ask you to see if you can reproduce the issue with a recent software version?

If you can reproduce the issue, please change the status to "CONFIRMED" when replying. Thank you!

Comment 2 Bug Janitor Service 2022-11-05 05:08:54 UTC

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

Comment 3 Rolf Eike Beer 2022-11-07 06:55:00 UTC

Still happens with current version, just toggle between globe and mercator.

Comment 4 Torsten Rahn 2023-04-22 13:54:19 UTC

Yes that is a conceptual problem.
Currently we have several mechanisms in place that try to allow for "crisp" rendering across projections. 
On one hand there is the "discrete" property that can be specified in the maptheme's DGML-file in order to have zooming via the mouse-wheel "locked" to the "best values":

<dgml xmlns="http://edu.kde.org/marble/dgml/2.0">
  <document>
    <head>
      <name>OpenStreetMap</name>
      <zoom>
        <discrete> true </discrete>
      </zoom>
    </head>

In addition to this we have the option to zoom via "+" and "-" which also "locks" to the "best values".

The best values get determined via the methods 

int TextureLayer::preferredRadiusCeil( int radius ) const

and 

int TextureLayer::preferredRadiusFloor( int radius ) const

Their implementation returns "best values" which are chosen relative to the tile dimensions (and their inherent projection which is Mercator for many and Equirectangular for others). This means that the most "crisp" rendering can be achieved if the user-selected projection matches the actual tile-projection.  For all other projections (like spherical) the rendering will differ a bit (resulting in an "apparent height difference" as you described it). A "better" implementation might apply another projedtion-dependent multiplication factor to the "preferredRadiusFloor/Ceil"-result. However that requires some additional "tinkering".