allow custom formatter when using the hover tool

[scaine1]

Background
The python library geoviews (http://geoviews.org/) uses bokeh as a backend when interactive plotting geographical data is required.
Typically data on a latitude/longitude grid is converted to a Web Mercator projection and displayed using bokeh.

The Issue
When using the hover tool on data transformed in to Web Mercator format, the user is shown the transformed values for latitude/longitude rather than the original latitude/longitude values.
Attached is an image that shows this issue

There have some discussions on how to solve this issue at holoviz/geoviews#100 and it seems the consensus would be that the nicest way to solve the problem would be if a custom formatter could be applied to the hover tool.
This would allow the Web Mercator transformed data could be transformed back to latitude/longitude values when displayed by the hover tool.

As this feature does not already exist I expect that it may be a niche issue relating to geoviews, however would adding a custom formatter to the hover tool be something you would be willing to consider?

[bryevdv]

@scaine1 I think my immediate preference would be to :

• add a generic CustomJSFormatter that is similar to several other "CustomJS" type models elswhere in Bokeh.

• Add an example that demonstrates how to use it to format mercator values

• Holoviews and other high level tools can use it to provide "built in" support at that level

[scaine1]

sounds ideal to me!

[bryevdv]

@scaine1 Are you interested in working up this feature as a contribution? (Just asking, I could not tell if that's what you meant above by willing to consider)

[scaine1]

Unfortunately at this point I think it is beyond my abilities.
When I said ".. willing to consider .." I meant would the bokeh team be willing to consider adding this feature for me and other geoviews users. Sorry for not being clear.
Having said that, if you don't have anyone to work on it I could potentially dedicate some time over the next couple of months to learn how bokeh works and come up with a solution.

[bryevdv]

@scaine1 no worries I just wanted to clarify. I think this is useful enough that I will probably try to get to it sooner rather than later, but if you are looking to get involved with a project don't let that stop you, there's plenty of other issues :)

[github-actions]

This issue has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs.