[mapserver-users] ScaleHint

[Rob Atkinson]

Daniel Morissette wrote:

> Rob Atkinson wrote:
> >
> > Yep - ignoring this functionality will definitely make the software less than
> > safe to deploy.
> >
>
> Rob,
>
> I'm not sure to understand why deploying a server as it is today would
> be unsafe?  Could you please specify the risk?  If there is a problem
> (other than the absence of the ScaleHint in the capabilities) I would
> like to address it.
>
> Note that in the current implementation if MAXSCALE is exceeded then
> the layer is simply not drawn... so if the risk you were expecting was
> an overload of hte server then it is not the case.
>

Cool - I misunderstood the original message then. Its not mapserver per se that
would be a problem but a configuration that did not restrict scale for large data
sets.

>
> > Well behaved clients will respect the scale-hint. The mapserver should, IMHO,
> > generate an error if the scale hint is exceeded - its not quite as strong as
> > that but it really ought to be mandatory behaviour.
> >
>
> I see your point, but I would personally opt for a smoother behavior,
> that is: not rendering the layer in the result image if scalehint is
> exceeded... the reason being that very simple clients that ignore
> scalehint would rather receive a blank image than an error IMHO... and
> it is assumed that well behaved clients will *not* request anything
> outside of scalehint, so what we do in this case is irrelevant to them.
>

Agree with you - noting that a blank image format is a valid error response. And
the second way you phrased it is better than the first: not rendering is not as
sensible as not requesting in the first place!

>
> I haven't found anything in the 1.1.0 spec about what the expected
> behavior is when a request outside of scalehint is received... I'll
> forward the question to the WMS-Dev list to make sure that what we do in
> MapServer is in line with what the others servers do and expect.
>

This is what I meant when I said that this behabviour is not currently mandated.

>
> --
> ------------------------------------------------------------
>  Daniel Morissette               morissette at dmsolutions.ca
>  DM Solutions Group              http://www.dmsolutions.ca/
> ------------------------------------------------------------
>   Don't put for tomorrow what you can do today, because if
>       you enjoy it today you can do it again tomorrow.
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