[Qgis-psc] RFC for Data Frames

[Benedict Holland]

Hi all,

So this then asks a fairly fundamental question: what exactly would I be
developing? The data frame could handle rendering but I suppose that it
would just be a question of if want the QgsProject to handle it or push it
down a level. I like the idea of data frames handling it the more I think
about it however. This would actually closely mimic what the QgsProject
does currently. If we go down this route, would it be fair to call it a
subproject ie QgsSubproject? I think that this would fully encapsulate the
idea that I am creating a way to generate projects which would have
multiple layers, link to different subprojects, have a canvas, legend,
display properties, interactions with the Composer, etc. I like this name
also because it has a direct link to QgsProject in that a QgsProject is
made up of QgsSubproject objects. This is a logical grouping which makes
more sense than data frames.

The huge downside to this is that a change like this could break a lot more
code than a smaller change like just having the data frame be a simple
collection of layers. I would be impacting quite a lot of code with these
changes. I am not familiar enough with how a canvas is actually displayed
yet or how the composer displays objects to know if my changes would force
a lot of changes. I don't particularly want to be rewriting most of QgsCore
as a first project, alone.

Also a huge problem that I see with this project is that I don't have a
good way of coding in the way that is specified in the CODING doc where I
would have something like load() loadNew() because I
am fundamentally changing what entire classes do and how they relate to
each other. If no one else is working in this area then I can basically do
what needs to be done but merging code when object relationships change is
very difficult and I have not seen a great way to manage that process. If
there are no complaints then I will edit the RFC to reflect the
QgsSubproject principal and send out an updated RFC to the list serve.

Thanks,
~Ben

On Wed, Jan 9, 2013 at 11:15 AM, Marco Hugentobler <
marco.hugentobler at sourcepole.ch> wrote:

>  Hi Benedict
>
> It is a good direction to go towards multiple views / dataframes. This is
> a frequent feature-wish and it is good to know someone is working on it.
>
> The RFC is centered around data frames as layer collections, but I think
> it would involve more than just QgsProject and QgsMapLayer. E.g. every
> frame could have it's own canvas / layer set / output crs (maybe even
> legend, overview map). Therefore, the term data frame may need to be
> changed.
>
> Once you are working on QgsProject, don't forget that layers and whole
> groups can be embedded from other projects / frames.
>
>
> Regards,
> Marco
>
>
>
> On 09.01.2013 01:04, Benedict Holland wrote:
>
> Hi All,
>
>  I don't know if I can actually call this project data frames as I don't
> know if that is TMed by ESRI but regardless the concept is the same. The
> RFC is located here:
>
>  http://hub.qgis.org/wiki/quantum-gis/Data_Frames
>
>  This would be a substantial change to the current architecture of
> QgsProjects and the relationship between QgsProjects and QgsMapLayers. I
> have been a professional developer for about 6 years or so and have worked
> on projects much larger than this but not in c++ for quite some time. I do
> though use best practices including unit tests and documentation as part of
> a standard development procedure and I applaud your requirements that these
> be included in this feature. While I do expect this will change
> the architecture I do not expect much will break unless previous releases
> cannot load a project file from a future release but honestly, there is
> little I or anyone else can do about that now except tell people to
> upgrade. If there isn't currently a way to handle future releases then I
> will also create a method for doing that and file it under the same RFC
> linked above.
>
>  Let me know what you can think. I am eager to get working on this as it
> would make life substantialy easier for me in the direct future.
> ~Ben Holland
>
>
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>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Weberstrasse 5, CH-8004 Zürich, Switzerlandmarco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee
>
>
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