[Geoprisma-dev] Attribute filtering

[Etienne Dube]

Hey Julien,

Digging deeper into GeoExt, I've come across the FormPanel widget which 
is somewhat close to what we need. It's quite basic (supports only a 
list of criteria that are combined by AND or OR, no possibility to 
combine different logical operators and set their precedence) but 
nevertheless that's a good starting point, and it's easier to use than 
the GXP widget I mentioned. I'll play with that for a while before 
trying to reinvent the wheel, and will try to build a GP widget around 
it. GeoExt (and ExtJS itself) is more complex than I expected, it's 
taking me some time wrapping my brain around it...

Etienne



On 02/11/2010 12:30 PM, Julien-Samuel Lacroix wrote:
> Hi,
>
> After giving it some thought on my side, I think the best way to go is 
> as you describe. Develop a GeoExt UX that allow attribute filtering 
> and apply it only on the client side in the beginning. Then when we 
> will want more performance, we will add a WFS service type in 
> GeoPrisma and modify the UX to support WFS Filter.
>
> I advise you to contact the GeoExt-dev list right away though. You 
> will probably have some nice feedback. Also create yourself a sandbox 
> in GeoExt SVN and put your code there.
>
> Julien
>
> On 10-11-02 10:06 AM, Etienne Dube wrote:
>> Hi Alexandre,
>>
>> We don't need access control based on filters for this specific project,
>> but it's still something that's on our wishlist. I see that as somewhat
>> different from the attribute filtering widget, since this kind of access
>> control would have to be implemented server-side (probably by putting
>> some logic in the proxy) to offer any real security.
>>
>> I started coding a first chunk of the widget, and will post to
>> GeoExt-dev when I have something to show.
>>
>> Thanks for your feedback,
>>
>> Etienne
>>
>>
>>
>>
>> On 01/11/2010 8:12 AM, Alexandre Dube wrote:
>>> Etienne,
>>>
>>> I totally agree that this could be a GeoExt.ux widget. All the
>>> features you mentioned about it have no direct dependence on
>>> GeoPrisma. A thread could be started on the GeoExt-DEV ML.
>>>
>>> In you project, do you need any access control using filtering ? For
>>> example, "restrict the data X to a given extent and a given attribute
>>> having a specific value to the user Y". If so, that could be discussed
>>> here.
>>>
>>> Regards,
>>>
>>> Alexandre
>>>
>>>
>>> On 10-10-29 03:11 PM, Etienne Dube wrote:
>>>> Hi guys,
>>>>
>>>> We have a new requirement in one of our projects, that involves
>>>> attribute filtering on a vector layer. What's needed is a widget that
>>>> allows the user to filter the features to be displayed by specifying
>>>> an attribute, an operator and a comparison value. One or more of
>>>> these criteria could be combined using logical operators (AND/OR) to
>>>> create more complex queries; eventually multiple filtering
>>>> expressions could be combined by forming a tree of conditions,
>>>> similar to what the OGC Filter Encoding standard describes. Such a
>>>> feature has already been discussed previously (see ticket
>>>> http://trac.osgeo.org/geoprisma/ticket/38).
>>>>
>>>> I spent some time defining the problem and exploring what tools could
>>>> be used to solve it. A few thoughts:
>>>>
>>>> - We could offer two different modes for this widget:
>>>>
>>>> 1. A preconfigured mode, in which the choices of attributes (and
>>>> possibly operators) to filter on, along with the logical operators
>>>> used to combine these criteria, would be defined in the widget's
>>>> configuration. Different preconfigured query templates could be
>>>> defined in this way, for every layer the widget applies to. The user
>>>> would only have to fill in the values to filter on.
>>>>
>>>> 2. An "expression builder" mode. In this case, the choice of
>>>> attributes, operators and any logical combination (AND/OR) or
>>>> criteria would be left to the user, and a GUI panel would be provided
>>>> to build these expressions. This mode mostly targets GIS specialists
>>>> and other power users who have an understanding of boolean logic, in
>>>> order to fulfill various free-form querying needs.
>>>>
>>>> - Initially we could provide support for vector layers only.
>>>> OpenLayers already provides the OpenLayers.Filter classes to build
>>>> the filtering expressions, and is able to do filtering on the client
>>>> side. However, since it's not a particularly efficient way of doing
>>>> things, a way to pass the filter expression to the service would be
>>>> desirable. As Yves mentioned in ticket #38, FeatureServer offers
>>>> basic attribute filters as criteria passed in key/value pairs in a
>>>> GET request, but this support is quite limited: it seems that only 1
>>>> criteria per attribute is accepted, there's no way to combine
>>>> multiple criteria using AND/OR operators (AND is the default when
>>>> specifying a filter for more than 1 attribute) and only the PostGIS
>>>> data source is supported for attribute filters. Short of extending FS
>>>> and its protocol, a solution could be to add a WFS proxy and pass a
>>>> Filter Encoding expression in the request (as you may know, OL
>>>> already has the logic to generate an ogc:Filter element from
>>>> OpenLayers.Filter objects).
>>>>
>>>> - Support for filtering WMS layers (issued from vector sources) would
>>>> be a good idea too. I believe it's possible by passing an ogc:Filter
>>>> as part of a SLD in the GetMap request.
>>>>
>>>> - OpenGeo developed a QueryPanel widget (it's in their GXP
>>>> repository) that offers similar functionality; see
>>>> http://workshops.opengeo.org/geoext/more_ogc/app.html. I've not been
>>>> able to make it work yet, and from what I see it can only apply
>>>> filters on WFS and WMS layers. Nevertheless, this could be a good
>>>> starting point.
>>>>
>>>> - For the moment we can settle with text boxes for entering filter
>>>> values, but it would be interesting to offer other control types
>>>> (date picker, selection list). Another cool feature to have would be
>>>> the ability to populate such selection lists with domain values (e.g.
>>>> coming from a catalog table in the DB). However I'm not aware if any
>>>> feature service (be it FeatureServer, WFS or MapFish Server) can do
>>>> that kind of stuff, and I think it wouldn't be extremely elegant to
>>>> have to establish an off-the-band connection to the data source for
>>>> retrieving those domain value lists.
>>>>
>>>> I think that the widget could be developed as a GeoExt ux first,
>>>> since it's usefulness goes beyond the scope of GeoPrisma. I'm writing
>>>> here to have some initial feedback, and I'm open to continue the
>>>> discussion on the GeoExt dev mailing list if you feel it would be
>>>> more relevant there.
>>>>
>>>> Ideas, suggestions and corrections are welcome.
>>>>
>>>> Etienne
>>>>
>>>
>>>
>>
>>
>


-- 
Etienne Dubé
Consultant / Développeur

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