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CGContour with and without cell_fill keyword [message #89925]

Mon, 29 December 2014 09:03

envi35@yahoo.ca
Messages: 48
Registered: March 2005

Member

Hi all, I'm using CGContour to make maps of vegetation index. I found my maps look quite different when I plot with or without the /cell_fill keyword as in the following lines:

CGContour,lai,lon,lat,/cell_fill,c_colors=c_colors,Levels=us erLevels,max_value=dmax,min_value=dmin,C_CHARTHICK=2,/overpl ot, Color=black,missingvalue=nan

CGContour, lai,lon,lat,c_colors=c_colors,Levels=userLevels,max_value=dm ax,$
min_value=dmin,C_CHARTHICK=2,/overplot, Color=black,missingvalue=nan

I know David suggests using cell_fill for projected maps or data with missing values, I thought that's just for making the map looks good, e.g. without holes etc., but not different maps.

The map without the cell_fill keyword shows larger values (more realistic to me)than the map with the keyword. Does anybody knows why? Which map is correct?

Thanks very much,
Jenny

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Re: CGContour with and without cell_fill keyword [message #89926 is a reply to message #89925]

Mon, 29 December 2014 09:32

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Jenny writes:

>
> Hi all, I'm using CGContour to make maps of vegetation index. I found my maps look quite different when I plot with or without the /cell_fill keyword as in the following lines:
>
> CGContour,lai,lon,lat,/cell_fill,c_colors=c_colors,Levels=us erLevels,max_value=dmax,min_value=dmin,C_CHARTHICK=2,/overpl ot, Color=black,missingvalue=nan
>
> CGContour, lai,lon,lat,c_colors=c_colors,Levels=userLevels,max_value=dm ax,$
> min_value=dmin,C_CHARTHICK=2,/overplot, Color=black,missingvalue=nan
>
> I know David suggests using cell_fill for projected maps or data with missing values, I thought that's just for making the map looks good, e.g. without holes etc., but not different maps.
>
> The map without the cell_fill keyword shows larger values (more realistic to me)than the map with the keyword. Does anybody knows why? Which map is correct?

The one with the CELL_FILL keyword is correct. The other is completely
wrong. :-)

http://www.idlcoyote.com/color_tips/fill_colors.html

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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Re: CGContour with and without cell_fill keyword [message #89927 is a reply to message #89926]

Mon, 29 December 2014 10:14

envi35@yahoo.ca
Messages: 48
Registered: March 2005

Member

On Monday, December 29, 2014 12:32:39 PM UTC-5, David Fanning wrote:
> Jenny writes:
>
>>
>> Hi all, I'm using CGContour to make maps of vegetation index. I found my maps look quite different when I plot with or without the /cell_fill keyword as in the following lines:
>>
>> CGContour,lai,lon,lat,/cell_fill,c_colors=c_colors,Levels=us erLevels,max_value=dmax,min_value=dmin,C_CHARTHICK=2,/overpl ot, Color=black,missingvalue=nan
>>
>> CGContour, lai,lon,lat,c_colors=c_colors,Levels=userLevels,max_value=dm ax,$
>> min_value=dmin,C_CHARTHICK=2,/overplot, Color=black,missingvalue=nan
>>
>> I know David suggests using cell_fill for projected maps or data with missing values, I thought that's just for making the map looks good, e.g. without holes etc., but not different maps.
>>
>> The map without the cell_fill keyword shows larger values (more realistic to me)than the map with the keyword. Does anybody knows why? Which map is correct?
>
> The one with the CELL_FILL keyword is correct. The other is completely
> wrong. :-)
>
> http://www.idlcoyote.com/color_tips/fill_colors.html
>
> Cheers,
>
> David
>
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
> Sepore ma de ni thue. ("Perhaps thou speakest truth.")

Thanks! David. I guess the map with neither Fill nor Cell_Fill is more wrong?

Jenny

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Re: CGContour with and without cell_fill keyword [message #89930 is a reply to message #89927]

Mon, 29 December 2014 11:49

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Jenny writes:

> Thanks! David. I guess the map with neither Fill nor Cell_Fill is more wrong?

I think the point is, if you are going to fill your contour plot with
colors, the colors should match the contour intervals displayed on the
plot. They don't if you set FILL, they do if you set CELL_FILL, when
doing contouring onto a map projection.

I don't know what "more wrong" means in the above context. I do know it
is usually a mistake to choose the version that "looks better" if
scientific accuracy is what you are aiming for. :-)

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thue. ("Perhaps thou speakest truth.")

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