[mapguide-internals] MapGuide RFC 69 - Rendering Layer Styles

Fri Jun 26 11:11:43 EDT 2009

I'm not familiar with the specifics of FDO ordering, but yes if FDO had a way for you to set an "ordering filter" that controls how features are returned, then that would be the preferred way to address this since it would mean only one query.

But this just shifts the performance issue to FDO.  How would commonly-used providers like SHP and SDF implement that efficiently?

You may have another option - implement a utility which creates a data set optimized for a theme:
* the utility will read the layer definition containing the themes
* it will query the original data set once using each rule's filter, and write those features to a new data set (it needs to be a format which returns features in the order they were written)
* update your layer to use the new data set - the features will come in with the right order

-----Original Message-----
From: mapguide-internals-bounces at lists.osgeo.org [mailto:mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Zac Spitzer
Sent: Thursday, June 25, 2009 11:55 PM
To: MapGuide Internals Mail List
Subject: Re: [mapguide-internals] MapGuide RFC 69 - Rendering Layer Styles

So based on that, if FDO supported ordering both issues, that being
Scott's label
problem and the overlay of roads might be solved?

http://trac.osgeo.org/fdo/ticket/516

would that be more efficient than respecting the layer style order and
would also
allow complex overriding of the rendering order simply by manipulating
the column
used for order by?

z

On Fri, Jun 26, 2009 at 1:42 PM, Walt
Welton-Lair<walt.welton-lair at autodesk.com> wrote:
> In MapGuide the order of the rules has no influence at all on the feature rendering order or the label rendering order.  Features are processed in the order that FDO returns them.  If a feature corresponding to a local road is returned by FDO before a feature corresponding to a highway, then the local road gets rendered first - below the highway.
>
> Labels are processed in reverse order.  As we iterate over the features for all layers we build up a list of candidate labels.  Feature 1 on layer 1 adds its candidate labels, then feature 2 on layer 1, ...  Once all features on all visible layers have been processed we do the final processing of labels.  We iterate over the list of candidate labels in reverse order - top down in rndering order.  The last feature on the topmost layer has the first crack at displaying its labels.  Then the next-to-last feature on the topmost layer, and eventually you move to the next lower layer.
>
> This is the way MapGuide has worked since the very beginning (pre-MapGuide 6.5).
>
>
> I'm going to bed...
>
> ________________________________________
> From: scotth at mpowerinnovations.com [scotth at mpowerinnovations.com]
> Sent: Thursday, June 25, 2009 11:29 PM
> To: Walt Welton-Lair; MapGuide Internals Mail List
> Subject: RE: [mapguide-internals] MapGuide RFC 69 - Rendering Layer Styles
>
>        using Style Order
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 7bit
>
> Welt That was confusing...Are you saying if I put complex linestyles on highways and labels but leave local roads   simplex thats why the local road labels render before myy complex linestyle roads no matter how far up I promote thhem in thhhe theme...I have the same problem with polygons...If I move townships, villages, or cities to the top of my theme of muniipalities it seems to have no effect onlabeling priority at all...it seems almost random
>
> -----Original Message-----
> From: Walt Welton-Lair <walt.welton-lair at autodesk.com>
> Sent: Thursday, June 25, 2009 10:07 PM
> To: MapGuide Internals Mail List <mapguide-internals at lists.osgeo.org>
> Subject: RE: [mapguide-internals] MapGuide RFC 69 - Rendering Layer Styles
>        using Style Order
>
> "Can some elaborate on how the server currently handles this?"
> Handles what?
>
> The current code iterates once over the features (ignore the compound line style example).  For every feature it evaluates the filters defined by the rules (in the order that the rules are specified).  Once it finds a matching rule it applies its style to the feature.
>
> With compound line styles we make a pass over all the features for each line style.  So for a compound line style containing M styles we make M FDO queries.
>
> With rendering passes (RFC 29) we also iterate over all the layer's features for each rendering pass.  The more passes you define the more queries you make.
>
> How to implement your RFC?
>
> option 1
> - Make a pass over the features for each rule.
> - During each pass only render the features that satisfy the rule for that pass.
> - If there are M rules you will make M FDO queries.
> => performance (speed) will be unacceptable for anything more than a few themes
>
> option 2
> - Make one query against all the features, remembering (in memory?) all the feature information (attributes / geometry) needed by stylization.
> - During the initial pass render the features for the first rule.
> - Iterate over the remaining rules in order, rendering the features for each rule.
> => performance (memory use) will be unacceptable for data sources containing large numbers of features
> => this approach goes against the MG architecture of not keeping feature data in memory during stylization (we already break that rule with labels which is what leads to high memory usage spikes for some maps)
>
> option 3
> - Allocate one image per rule.
> - Make one query against all the features, and render each feature into the image corresponding to the rule it satisifes.
> - Merge all images at the end.
> => performance (speed + memory) will be unacceptable for anything more than a few themes
>
> option 4
> ???
>
>
> ________________________________________
> From: mapguide-internals-bounces at lists.osgeo.org [mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Zac Spitzer [zac.spitzer at gmail.com]
> Sent: Thursday, June 25, 2009 10:36 PM
> To: MapGuide Internals Mail List
> Subject: Re: [mapguide-internals] MapGuide RFC 69 - Rendering Layer Styles      using Style Order
>
> At the moment the only way to achieve this is to split the road network out into
> multiple layers which is rather ugly.
>
> Taking a road network as the example here, it's only at the
> intersections where this
> problem occurs.
>
> Can some elaborate on how the server currently handles this?
>
> z
>
> On Fri, Jun 26, 2009 at 12:28 PM, Walt
> Welton-Lair<walt.welton-lair at autodesk.com> wrote:
>> "Proposed solution: Add support to the rendering engine to render layer styles in ordered passes."
>>
>> I'd like to see some concrete suggestions in the RFC on how to actually do this efficiently.  Just consider a conservative use case - say around 10  rules.
>>
>> Walt
>> ________________________________________
>> From: mapguide-internals-bounces at lists.osgeo.org [mapguide-internals-bounces at lists.osgeo.org] On Behalf Of Zac Spitzer [zac.spitzer at gmail.com]
>> Sent: Thursday, June 25, 2009 9:29 PM
>> To: MapGuide Internals Mail List
>> Subject: [mapguide-internals] MapGuide RFC 69 - Rendering Layer Styles using    Style Order
>>
>> I have posted a new RFC
>>
>> http://trac.osgeo.org/mapguide/wiki/MapGuideRfc69
>>
>> --
>> Zac Spitzer -
>> http://zacster.blogspot.com
>> +61 405 847 168
>> _______________________________________________
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>> mapguide-internals at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/mapguide-internals
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>> mapguide-internals at lists.osgeo.org
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>>
>
>
>
> --
> Zac Spitzer -
> http://zacster.blogspot.com
> +61 405 847 168
> _______________________________________________
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> mapguide-internals at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapguide-internals
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-- 
Zac Spitzer -
http://zacster.blogspot.com
+61 405 847 168
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