[ncl-talk] Difficulty overlaying xy line overtop polygon and background text

[Adam Phillips]

Hi Andrew,
I (unfortunately) have plenty of experience with draw order issues with
polygons, polylines and text. It can get quite frustrating. If memory
serves, there's a weird quirk where NCL only listens to one tfPolyDrawOrder
setting for all polygons/polymarkers/polylines/gsn*text, regardless if you
set this 3 different ways in 3 different resource lists.

You spoke of two issues you are having:
*1 - When the polygons get drawn, regardless of whether I set the draw
order to PreDraw or not, they are on top of the xyline and the
points/labels.*
I don't see this issue in the plot you sent, so I must be missing
something. The orange line is on top of the green and beige polygon boxes.

*2 - The other issue I have is that I am trying to get the xy-line and the
point labels to be on top of the text that I overlay (such as the
"Elevated" label in the attached image).*
This issue I do see, as the "8" on the 7am Monday reading is getting
overwritten by the "Elevated" text.

Things to try (in no particular order):
1 - For any text that you want to be on top (and overlay everything else)
call these sections of code *after* you call draw(plot). This
technically should fail, but it's a work around I've used successfully
before.
2 - Along the same lines, try moving different code sections around,
calling the text/polylines etc that you want on top as near to the end as
possible. Again, the order of your code shouldn't alter anything, but
sometimes it does.
3 - If this is going to be a static image, the sizes of everything are not
changing and the NDC coordinates of anything will not change, and you are
not paneling, the big hammer would be to draw the polygons, the gsn_csn_xy
line, the line value labels, and the legend. Then call draw(plot), but then
use gsn_text_ndc to place the "High/Moderate..." exactly where you want it.
4 - Use gsn_add_text instead of gsn_text if you can.

This is definitely a weakness in NCL's graphics. It would be great if NCL
had something akin to what is done with other software with layers, where
you can say put this label on top of this line on top of this polygon and
so on.  When I have a number of polygon/polyline/polymarker calls, and I
have to mess with the draw order of the various objects, I know that
there's a good chance that I will have to partake in a fair bit of trial
and error.  Hopefully you are able to figure things out.
Hope the above helps,
Adam





On Sun, Sep 5, 2021 at 8:36 AM Andrew Kren - NOAA Federal via ncl-talk <
ncl-talk at mailman.ucar.edu> wrote:

> Hi ncl-talk,
>
> Sorry for the bother. I am making an xy plot where I plot the xy-line
> along with points labeling the values at certain intervals. I am
> overlapping polygons to specify different levels of the xy values using
> gsn_add_polygon. When the polygons get drawn, regardless of whether I set
> the draw order to PreDraw or not, they are on top of the xyline and the
> points/labels. I even set my xyline draw order to PostDraw and that does
> not seem to alleviate it. The other issue I have is that I am trying to get
> the xy-line and the point labels to be on top of the text that I overlay
> (such as the "Elevated" label in the attached image). I was not able to
> find a setting to set the draw order of text so any input is appreciated.
>
> I appreciate any help you can provide. I attached my script for
> convenience.
>
> --
>
> Andrew Kren
> Meteorologist
> NOAA's National Weather Service
> Raleigh Forecast Office
> 1005 Capability Drive, Suite 300
> Raleigh, North Carolina 27606
> voice: 919-326-1035
> mailto: andrew.kren at noaa.govhttp://www.weather.gov/rah
>
>
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-- 
Adam Phillips
Associate Scientist,  Climate and Global Dynamics Laboratory, NCAR
www.cgd.ucar.edu/staff/asphilli/   303-497-1726

<http://www.cgd.ucar.edu/staff/asphilli>
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