[gradsusr] Create boolean map applying threshold

[Alauda arvensis]

Thank you very much Doug! Works perfectly. You made my day!

Cheers,
Chris
On Fri, Jun 24, 2011 at 2:00 PM, Clark, Douglas B. <dbcl at ceh.ac.uk> wrote:

> Chris,
>
> You need to define a variable along the lines of
>
> define newvar=const(const(maskout(var,var-2),1),0,-u)
>
> where var is the existing variable that you want to apply the threshold to.
>
> This is a rather complex expression, so you might want to build it up in
> parts (e.g. 3 lines), starting with the inner maskout so you can work out
> what's going on. See the GrADS documentation for the maskout and const
> functions.
>
> In fact I think this will set newvar to 1 where var>=2 (i.e. >= rather than
> > ), so if you really want to exclude values that are "exactly" (meaning
> "close to"!) 2 you could use something like "var-2.00001".
>
> In any case, check that you get the answer you want/expect!
>
> (Your example didn't work because you were manipulating scalar variables in
> the GrADS scripting language, not gridded variables.)
>
> Doug
>
>
>
> From: gradsusr-bounces at gradsusr.org [mailto:gradsusr-bounces at gradsusr.org]
> On Behalf Of a.arvensis at gmail.com
> Sent: 24 June 2011 11:28
> To: gradsusr at gradsusr.org
> Subject: [gradsusr] Create boolean map applying threshold
>
> Dear Grads users,
>
> I have a grid with varying values (t). From this grid I want to create a
> boolean grid where a value of (1) is assigned to all grid cells above a
> certain threshold (2) and the value of (0) is assigned to all other values.
> This would be something like:
>
> if (t > 2); t = 1; else t = 0; endif
>
> The line above does not work and my feeling is that such conditional
> statements cannot be applied to grid cells, but are rather meant to control
> the flow of your script. What approach is appropriate? Thank you very much
> in advance!
>
> With kind regards,
> Chris
> --
> This message (and any attachments) is for the recipient only. NERC
> is subject to the Freedom of Information Act 2000 and the contents
> of this email and any reply you make may be disclosed by NERC unless
> it is exempt from release under the Act. Any material supplied to
> NERC may be stored in an electronic records management system.
> _______________________________________________
> gradsusr mailing list
> gradsusr at gradsusr.org
> http://gradsusr.org/mailman/listinfo/gradsusr
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20110624/5e67ecbb/attachment-0003.html