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Re: [ferret_users] ppl commands for a Vector overlay on a projection.



Hi Alexander,

I haven't tried your examples in any detail, but I think for the map projection vector overlay to work correctly, you would need to have the vector variables on the same grid as the underlying plot.  That way the x_page, y_page coordinate variables are defined once and are consistent for the plot:

USE RawERA5WindSpeed500Annual.nc
USE RawERA5WindSpeedComp500annual.nc
go mp_mcbryde_fpq
go mp_grid p[D=1]

Set window/asp=0.7 1
SHADE/PALETTE=difference/nolab/LEVELS=(-38, 38, 2) p[D=1], x_page, y_page

let uwnd_ov = uwnd[d=2,gxy=p[d=1]]
let vwnd_ov = vwnd[d=2,gxy=p[d=1]]

VECTOR/overlay/Thickness=0.25/Xskip=60/Yskip=40/set Uwind_ov, Vwind_ov, x_page, y_page
ppl VECSET 0.25,25
ppl VECKEY/NOUSER 3.5,1,,(f3.0," m/s")
ppl vector/overlay




On 6/21/2021 9:05 AM, Alexander Audet wrote:
Hello ferret community,

                    Not sure if this is an impossible combination, but I was trying to see if I could refine my vector overlay over my projected shade. In one method, I try to use PPlus commands after setting up the vector overlay, however, without fail this creates a black map and does not seem to produce the desired effect with the legend.

USE RawERA5WindSpeed500Annual.nc
USE RawERA5WindSpeedComp500annual.nc
go mp_mcbryde_fpq
go mp_grid p[D=1]
go mp_grid Vwind, Uwind
Set window/asp=0.7 1
SHADE/PALETTE=difference/nolab/LEVELS=(-38, 38, 2) p[D=1], x_page, y_page
VECTOR/overlay/Thickness=0.25/Xskip=60/Yskip=40/set Uwind, Vwind, x_page, y_page
ppl VECSET 0.25,25
ppl VECKEY/NOUSER 3.5,1,,(f3.0," m/s")
ppl vector/overlay
GO mp_land
go mp_label 675,80,0,0,0.13  "ERA5"
PPL COLOR,6,50,50,50
Go mp_graticule 0, 360, 20, -90, 90, 20, 6, 1

In another variation, I can use PPlus commands before shading, however, while this does impact the standard vector length, and the format of the vactor key, it does not place the key where desired. It even seems to have mixed results about getting the scale correct, and I think when it gets it correct, it might just be due to rounding.

USE RawERA5WindSpeed500Annual.nc
USE RawERA5WindSpeedComp500annual.nc
go mp_mcbryde_fpq
go mp_grid p[D=1]
go mp_grid Vwind, Uwind
Set window/asp=0.7 1
SHADE/PALETTE=difference/nolab/LEVELS=(-38, 38, 2)/set p[D=1], x_page, y_page
ppl VECSET 0.25,25
ppl VECKEY 1,1,,(f3.0," m/s")
ppl shade
VECTOR/over/NOLABELS/KEY/Thickness=0.25/Xskip=60/Yskip=40 Uwind, Vwind, x_page, y_page
GO mp_land
go mp_label 520,80,0,0,0.13  "ERA5"
PPL COLOR,6,50,50,50
Go mp_graticule 0, 360, 20, -90, 90, 20, 6, 1

I can live without the scale placement as I can always move it in illustrator, though it may be a pain to keep it the correct size when resizing my images, however not being able to control the scale could be a dealbreaker.

Cheers!

Alexander

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