[ncl-talk] emphasize every parts of a line with different colors according to its y value.

[Alan Brammer]

my bad, forgot to switch out one of my personal shortcuts in the demo function. 
< df(wks, plot) 
===
> draw(plot)
> frame(wks)


> On 30 Dec 2016, at 14:59, Alan Brammer <abrammer at albany.edu> wrote:
> 
> ok, so there are multiples ways to plot a line.  
> Here’s my method which is over complicated for a single line but has massive speed benefits if you want to plot multiple lines.  
> 
> Similar to the previous replies, you can use the relatively undocumented gsSegments and gsColors resources to do pretty much what Rick describes but with better scaleability. 
> 
> Attached function with hopefully sufficient comments to explain whats going on and includes an inline demo function at the bottom I put together a while back.  
> 
> To run the demo either load the script and call colored_line_demo() or comment out lines 127/128 and then `ncl add_colored_line.ncl` will run it as the main script. 
> 
> Note to devs, attached in this script is an extended version of get_color_index() to accept an array of "value". Could this be included in the main function, it's a trivial edit and retains backwards compatibility. 
> 
> 
> <add_colored_line.ncl>
> Alan.
> 
> 
>> On 30 Dec 2016, at 14:21, Guido Cioni <guidocioni at gmail.com <mailto:guidocioni at gmail.com>> wrote:
>> 
>> I was going to reply with a similar recipe :) 
>> 
>> Basically, when drawing the line you have to split every segment and assign a color based on the average value of the y in that segment. 
>> This is just an hint, you will have to complete the code.
>> 
>> Assuming you have x,y which are your data values:
>> 
>> levels=fspan(min(y), max(y), 20)  ; define the levels for the colors, you can change this but it will always depend on the number of segments
>> 
>> cmap = read_colormap_file("amwg_blueyellowred") ; define the colormap that you want to use
>> 
>> do i=0,dimsizes(y)-1  ; loop over the segments 
>>    res at xyLineColors=GetFillColor(levels,cmap,avg((/y(i),y(i+1)/)))
>>    gsn_polyline(wks,plot,(/x(i),x(i+1)/),(/y(i),y(i+1)/),lres) 
>> end do
>> 
>> Guido Cioni
>> http://guidocioni.altervista <http://guidocioni.altervista/>.org
>> 
>>> On 30 Dec 2016, at 17:35, Rick Brownrigg <brownrig at ucar.edu <mailto:brownrig at ucar.edu>> wrote:
>>> 
>>> Hi,
>>> 
>>> I don't know of any way of doing this other than to draw the line piecewise.  What about something like:
>>> 
>>> datadims = dimsizes(data)  ; assuming your data is 2xN
>>> numlinesegs = datadims(1) - 1
>>> linesegs = new((/ numlinesegs/), graphic)
>>> do i=1,numlinesegs
>>>   color = ....appropriate logic to determine the color here...
>>>   res at gsLineColor = color
>>>   linesegs(i) = gsn_add_polyline(wks, plot, data(0, i-1:i), data(1, i-1:i), res)
>>> end do
>>> 
>>> This is not particularly efficient, and there may be better ways of doing this, but that should work.
>>> 
>>> HTH...
>>> Rick
>>> 
>>> 
>>> On Fri, Dec 30, 2016 at 12:48 AM, grace <313695096 at qq.com <mailto:313695096 at qq.com>> wrote:
>>> Hi:
>>>   All,I am trying to  draw a line  that emphasize every parts of it with different colors.
>>> I have found the example xy_12.ncl which highlight the wanted part by split the data.
>>> But I want to draw a line which have different colors according to its y numberical value,just like the plot below.
>>> <0356412F at 5DA70B25.65116658.png>
>>> If I split the data ,that would be a huge work.
>>> Have anybody drawed plot like this ?Any information will be appreciated.
>>>  
>>>  
>>> 
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