[Qgis-developer] show grid on map canvas (similiar to grid used in composer) - strategy?

[Etienne Tourigny]

On Thu, May 10, 2012 at 9:25 AM, Etienne Tourigny
<etourigny.dev at gmail.com> wrote:
> On Thu, May 10, 2012 at 9:06 AM, Nathan Woodrow <madmanwoo at gmail.com> wrote:
>> I think if QgsPluginLayer is a usable option that would be the way to go, or
>> maybe  QgsVectorLayer  but I suspect that you will need a provider for
>> that.
>
> Is there a way we can create a QgsVectorLayer in memory, without using
> a provider? If not , perhaps we could use a OGR in-memory dataset
> ('/vsimem/') - is this used currently somewhere in qgis?

nevermind - just saw QgsMemoryProvider!

Any way the provider classes could be in the API documentation???

>
> Another idea - use a QgsPluginLayer which itself contains a number of
> QgsVectorLayers (e.g. polygon + polylines) to remove the need to
> create a provider - but this might be cumbersome.
>
> I'm definitely interested in collaborating with others in this!
>
> Etienne
>
>>
>> I think having it show up in the legend is a good idea that way it can be
>> turned on and off, styled, and ordered as the user needs.  E.g. sometimes I
>> might like to have yellow grid lines rather then black.
>>
>> - Nathan
>>
>> On Thu, May 10, 2012 at 10:01 PM, Etienne Tourigny <etourigny.dev at gmail.com>
>> wrote:
>>>
>>> On Thu, May 10, 2012 at 1:35 AM, Alister  Hood
>>> <Alister.Hood at synergine.com> wrote:
>>> >> Date: Wed, 9 May 2012 18:00:07 -0300
>>> >> From: Etienne Tourigny <etourigny.dev at gmail.com>
>>> >> Subject: [Qgis-developer] show grid on map canvas (similiar to grid
>>> >>         used in composer) - strategy?
>>> >> To: qgis-developer <qgis-developer at lists.osgeo.org>
>>> >> Message-ID:
>>> >>
>>> >> <CA+TxYvPd-5VHoyCX4UHio9X416hKx9ZGeQ5EnnnQVaDP0L9ZCg at mail.gmail.com>
>>> >> Content-Type: text/plain; charset=ISO-8859-1
>>> >>
>>> >> Hi all,
>>> >>
>>> >> I would like to add support to draw a grid on the map canvas, in a way
>>> >> similar to what is done in the map composer (although perhaps without
>>> >> the annotations on the borders).
>>> >>
>>> >> What should be the approach used?
>>> >>
>>> >> 1) plugin or core?
>>> >> 2) rubberbands or basic plot functions triggered after mapCanvas
>>> >> update?
>>> >>
>>> >> I think both drawing strategies are possible using a plugin.
>>> >>
>>> >> It would be best to write in the core, assuming there is sufficient
>>> >> interest in this, but it will take time to trickle down to the stable
>>> >> version (an argument for making it a plugin).
>>> >>
>>> >> I know the current workaround is to create a vector grid with ftools,
>>> >> but that is a little clunky.
>>> >>
>>> >> Any thoughts?
>>> >> Etienne
>>> >
>>> > Hi,
>>> > I'm not a developer, so this might be a crazy and unnecessary idea, but
>>> > would it be feasible to create a graticule _provider_?
>>> >
>>> > This approach would mean that like grids created with ftools, the grid
>>> > would be created as a layer, but it wouldn't be file based and its extents
>>> > would automatically update.
>>> >
>>> > Unlike the approach used in the composer, this would mean:
>>> > - digitising tools could snap to the grid lines.
>>> > - the identify tool could identify the grid lines.
>>> > - the layer could be used for analysis (e.g. you might want to use it to
>>> > split vector layers).
>>> > - symbology and feature labelling could work just like other vector
>>> > layers.
>>>
>>> Those are pretty cool ideas!
>>> Perhaps a new QgsMapCanvasItem, rather than a provider? Or even a new
>>> QgsPluginLayer or QgsVectorLayer, so this is actually a layer? In this
>>> case the layer would have to be in the legend, whereas it might be
>>> better to hide it from the legend.
>>>
>>> >
>>> > If this was to actually replace the grids in the composer, some
>>> > improvements to feature labelling would be needed.  Some of these would
>>> > probably be good to have anyway, e.g. an option to label both ends of a
>>> > line, and an option to align labels horizontally or vertically on the page,
>>> > rather than N-S or E-W.  I guess the difficult one would be providing a way
>>> > to display labels outside the map frame...
>>>
>>> This kind of modification would require modifying the core rather than
>>> making a plugin I think.
>>>
>>> >
>>> > Regards,
>>> > Alister
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>>
>>