[mapguide-users] Is their a major flaw with theming point data?

[Jason Birch]

That might be tough to support properly given the complexity of the
stylization, especially because they can scale, be offset, etc based
on attributes.

Basically, you're stuck in a chicken/egg situation where you need the
data to calculate the symbol MBRs to figure out how much data to
request :)

Jason

On 2010-02-16, Miller, Craig <craig.miller at spatialminds.com> wrote:
> With the points, you could only fetch an over-post if there is a point layer
> that has a large symbol.  You could use the radius of the symbol to
> determine how much additional area to fetch.  You'd need MBRs for every
> possible symbol to be rendered before setting the map window MBR and
> fetching data.
>
> Craig
> On Tue, Feb 16, 2010 at 2:37 PM, Jason Birch <jason at jasonbirch.com> wrote:
>
>> How would you handle this James?
>>
>> The spatial intersection that MapGuide performs with the current
>> viewport's
>> extents is critical to performance when you are dealing with large amounts
>> of data, and many of the FDO data sources are optimized using R-Tree (or
>> similar) indices to return only the data which is currently in view.
>>
>> I guess you could conceivably fetch an over-post of the current extents by
>> some factor, but that would only work for a subset of point symbols (those
>> where the maximum dimensions of the theming is < half the expanded extent
>> dimension, and it would mean that everyone has to live with the decreased
>> performance of the over-fetch.
>>
>> A few options:
>>  - Make the over-fetch percentage or distance configurable per server, per
>> map, or per-layer
>>  - Only apply the over-fetch to points (there are actually cases where the
>> same problem happens with lines and polygons, so I don't think this is
>> valid)
>>
>> I personally feel that the current behaviour is generally OK, but there
>> are
>> definitely cases where you wouldn't want features missed just because
>> their
>> mid-point isn't in the current view extents.
>>
>> Regardless of the solution, I think this would take some work, so might
>> require some funding or somehow making it important to one of the
>> developers.
>>
>> Jason
>>
>>
>> On 16 February 2010 12:06, JamesDudden  wrote:
>>
>>> I understand how it happens and it does make sense but it renders the
>>> theming of points useless if they are going to be anything larger than a
>>> few
>>> pixels.
>>>
>>> I think it would be good to see future versions of Mapguide become more
>>> intelligent and be able to cope with theming of points.
>>>
>>>
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>>
>
>
> --
> Craig Miller
> Geospatial Software Architect
>