[gradsusr] Basemap with polar projection in circle frame

[David Nielsen]

Dear Grads users,

I am trying to use a north polar stereographic projection with basemap to
cover land areas in Grads.

Using the combination of set lat/lon and mproj suggested in basemap's
script, I get a nice map framed with a square:

'set lat 0 90'
'set lon -180 180'
'set mproj nps'
'set mpvals -180 180 50 90'
...
'set rgb 88 200 200 200'
'basemap L 88 1 L'



No problem there. Now, I would like to get rid of the corners of the
square, setting the minumin latitude to 50 and using the "set frame"
command, aiming to get a circle-shaped figure:

'set lat *50* 90'
'set lon -180 180'
'set mproj nps'
'set mpvals -180 180 50 90'
*'set frame circle'*
...
'set rgb 88 200 200 200'
'basemap L 88 1 L'

But then I get some pieces of land streching out of the circle:



Trying other mpdset and basemap resolutions doesn't solve the problem.

It can get even more messy with different map domains:




Has someone run into this or found a solution to this bug?

Many thanks in advance,
David
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