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

[Miller, Craig]

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
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