Provide user with option to control tile resolution hierarchy

[Keith Hughitt]

In order to make it possible for users interested in a particular type of non-SDO data (e.g. SWAP) which has a native resolution other than 0.6''/s, it would be useful to provide a mechanism to break away from the default zoom hierarchy.

Currently Helioviewer.org forces users to use one specific zoom hierarchy. This has a couple of advantages:

(1) Higher cache re-use
(2) Prevents minor browser differences in scale computation from creating two near-identical tiles

If the user was provided with a way to change this scale, these issues should be addressed or avoided, as much as possible.

POSSIBLE SOLUTION:

Create a drop-down in the user settings dialog where the user can select from different instruments. Helioviewer.org will then choose zoom-levels based on factors of that instrument's native zoom scale. By rounding to ~2-3 decimal places, most of the browser math differences would probably also be avoided. Most users probably won't bother to change this setting so the extra tiles in the cache should not be too bad, and by letting the user choose from a list of instruments instead of providing a free-form field, there is still the possibility for some cache re-use.

At the end of the day HV.org is still just a browse tool so even if the images are not perfect factors of the native image scale that is okay.

[Keith Hughitt (keith-hughitt)]

Might be nice to also include the actual scale in the dropdown list, e.g.:

SDO (0.6''/px)
SOHO (2.63''/px)
etc

(also, to be more clear: replace "instrument" with "observatory" in discussion above)