[Qgis-developer] Fwd: Re: Memory Layers - some proposals

[Matthias Kuhn]

Forwarded to list


-------- Forwarded Message --------
Subject: 	Re: [Qgis-developer] Memory Layers - some proposals
Date: 	Thu, 25 Sep 2014 06:04:19 -0800
From: 	Gary Sherman <gsherman at geoapt.com>
Organization: 	GeoApt LLC
To: 	Matthias Kuhn <matthias.kuhn at gmx.ch>
CC: 	gsherman at geoapt.com



On 9/25/14 1:10 AM, Matthias Kuhn wrote:
> Aren't there two different possibilities in which such layers can be used:
>
>   * As a scratch layer for the user, which he may want to save in the end
>   * As a means for plugins to show information to the user
>
> In the first scenario, the user may actually want to save the
> information because he realized in the process of drawing it, that it's
> valuable to him (if he would have known from the beginning, he could
> have started with a permanent layer type). In this case it would be nice
> to make the user aware of the risk of loosing data and offer him a
> simple way to save it (to an OGR supported format).
>
> In the second scenario, the information may be completely reproducible
> by the plugin or the information drawn by the user intercepted by the
> plugin and redirected to suitable places. In such a scenario a "Do you
> want to permanently save?" dialog would not be appropriate. And
> therefore there should be a possibility to disable it.

I agree---I have a plugin that uses memory layers to display information
abstracted from a database (with no QGIS data provider). This
functionality is essential and should not be changed, rather additional
features added to support interactive use through the UI.
>
> On the other hand, I also tend to use my /tmp folder on my machine for
> data I use to play around for the next couple of minutes but that I am
> completely aware of that it can be lost anytime (and I don't want my
> computer to ask me: "Hey, you have saved that download to /tmp and I'm
> going to delete it now, is that ok for you?"). So I tend to disagree
> with Sandros "why would you want to loose the data?" and answer it with
> "because it's intermediate, volatile and/or temporary."
>
> All in all: there are two scenarios, one with manual operation, one with
> plugins. The second one needs to be controlled by python, the first one
> is about awareness. This awareness can be achieved by one or more of the
> following
>
>   * Icons
>   * Message bar (e.g. when starting to digitize "You are digitizing on a
> temporary layer. Do you want to convert it to a permanent layer? Click
> here.")
>   * Message box when removing the layer from the canvas/closing the app
> "There is unsaved information, you will loose it unless you donate 5$ to
> the QGIS project. Click here"
>
> Or did I get this wrong?
>
> Matthias
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