Re: [matplotlib-devel] radial grids broken on polar?

That's right, Eric.  I think having resolution be an attribute of the 
artist (and not the projection) is the "path" of least resistance here.  
To clarify, however, the interpolation (more specifically, whether to 
interpolate) should remain a function of the projection, not the path.  
That's the important point that lead to it ending up in the wrong place 
in the first place.  If we aim to keep the generalization that all grid 
lines are the same kind of object regardless of the projection, and 
therefore set a high resolution parameter on all the grid lines, we 
wouldn't want this to slow down the standard rectilinear axes.  As long 
as the standard axes don't obey the parameter, then would should be 
fine.  It's somewhat confusing, but I also am seeing this the resolution 
parameter on artists as more of an implementation detail than a public 
API.  If someone wants to interpolate their data, IMHO that should be 
the user's responsibility, since they know the best way to do it.  This 
functionality isn't really about data points, IMHO.

The more difficult change seems to be being backward compatible about 
the Polar plot accepting a resolution argument.  I'm not even certain 
that it's worth keeping, since as you suggest, it makes more sense for 
it to be a property of the artist.  I'd almost prefer to raise a warning 
if the user provides a resolution argument (other than 1) to Polar 
rather than trying to make it work.  Is anyone actually using it, other 
than to set it to 1 on 0.98.x versions?

I should have some time to work on this today.

Mike

Eric Firing wrote:
> Eric Firing wrote:
>> Jae-Joon Lee wrote:
>>> The default resolution (which is used to interpolate a path in polar
>>> coordinate) has change to 1 at some point. And because of this, a
>>> radial grid becomes a 0-length line. Increasing the resolution will
>>> bring back your gridlines.
>>
>> This is not the right solution, though.  There was a reason for the 
>> change in default resolution to 1--it gives the expected behavior for 
>> plotting a line between two points in polar coordinates--and it is 
>> not going back.  The inability to set resolution on a per-artist 
>> basis is a serious problem that doesn't seem to have a simple 
>> solution.  Until one can be found, some sort of special case handling 
>> will be needed for the radial grid lines.
>>
>> Eric
>
>
> Expanding on this: it looks like a possible solution is to attach a 
> new "resolution" attribute to the Path object.  This would ordinarily 
> be None, but could be set to another value when the Path is created 
> (or later).  Then the PolarTransform.transform_path method (and the 
> same in other curvilinear projections) could use that value, if not 
> None, to control interpolation.  Some additional changes would be 
> needed to apply this to the radial gridlines.
>
> Now it is not clear to me that resolution should be an attribute of 
> the PolarAxes at all--the interpolation is done by a path method, so 
> that method doesn't need a resolution parameter at all if resolution 
> is a Path attribute.  Except for backwards compatibility.  Comments, 
> Mike?
>
> I can't implement it right now, but if no one comes up with a better 
> solution, or wants to implement something like this one, then I can do 
> it in a day or two.
>
> (Of course, I may not be seeing a stumbling block.)
>
> Eric

-- 
Michael Droettboom
Science Software Branch
Operations and Engineering Division
Space Telescope Science Institute
Operated by AURA for NASA