MapDisplayLab

[Jody Garnett-2]

Some javascript/style in this post has been disabled (why?)

Hi Michael;

Going over one of the example you provided (http://geotools.org/examples/displaylab.html)

... and I have a question :-)

You used the filter produced when they click ... and process the features into a Set<FeatureId>

Set<FeatureId> IDs = new HashSet<FeatureId>();
            try {
                while (iter.hasNext()) {
                    SimpleFeature feature = iter.next();
                    IDs.add(feature.getIdentifier());

                    System.out.println("   " + feature.getIdentifier());
                }

            } finally {
                iter.close();
            }

And then to display the features you create a Rule with ...

selectedRule.setFilter(ff.id(IDs));

Can I ask why you do not use the original filter? 

It could be:

- speed - avoiding a spatial test during every render - and using a feature id test would be fast

- teaching - it could be an excuse to process a feature collection

I am finding the page clear and well written; so I am loath to change anything :-)

I also usually produce a different filter when checking where someone clicks; I produce a 3x3 pixel bounding box; and then:

1) transform it to mappane crs (ie world coordinates)

2) transofrm it to the data crs (ie data coordinates)

On the grounds that a BoundingBox query is often the fastest spatial query you can do, faster then dwithin with less hard math.

Jody

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[mbedward]

Hi Jody,

> You used the filter produced when they click ... and process the features
> into a Set<FeatureId>
>
> Set<FeatureId> IDs = new HashSet<FeatureId>();

<snip>

> And then to display the features you create a Rule with ...
>
> selectedRule.setFilter(ff.id(IDs));
>
> Can I ask why you do not use the original filter?

I thought it might make each step a little more obvious, but now that
you point it out I'm not sure that it doesn't just make it seem more
complex :-)

You choose (and if any other list members have an opinion please speak
up - we'd love the feedback).

> It could be:
> - speed - avoiding a spatial test during every render - and using a feature
> id test would be fast
> - teaching - it could be an excuse to process a feature collection
> I am finding the page clear and well written; so I am loath to change
> anything :-)
> I also usually produce a different filter when checking where someone
> clicks; I produce a 3x3 pixel bounding box; and then:
> 1) transform it to mappane crs (ie world coordinates)
> 2) transofrm it to the data crs (ie data coordinates)
> On the grounds that a BoundingBox query is often the fastest spatial query
> you can do, faster then dwithin with less hard math.

Yes - that would be much better practice (and I'm noting it down for
my own future reference !). But do you think it would make the example
look even more complicated ?  On the other hand, perhaps when someone
has reached the point of braving this one we shouldn't be treating
them as a beginner and therefore your suggestion here would be better.

I was also planning to put a line or two of text on the page to
accompany each code box - you know, old-fogey style :)

Michael

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