[OpenLayers-Users] Interactive hot spots on a map for large, complex vector geometries

[Rob Marjot]

2014-07-01 23:03 GMT+02:00 Phil Scadden <p.scadden at gns.cri.nz>:

> On 1/07/2014 8:13 p.m., Rob Marjot wrote:
>
>> In my application (and my understanding of a responsive app) this isn't
>> acceptable (anno 2014).
>>
>
> Well your milage will vary. Even at anno 2014, web technology is not  up
> to managing a million vertices by download vector and js processing. If you
> have a small set of vectors then you can do it.


Well, it's not realistic that on the majority of the canvas' pixels there
will be a bend in the geometry. Therefore, the millions of vertices will be
reduced to only a fraction, for a given zoom and extent (by: clipping =>
quantizing => simplifying).


>
>  The usage scenario is going to be very "explorative": in the map there
>> will be all sorts of geometries statically visualized (WMS), while
>> interactive geoms (being query results) are to be drawn (and instantly
>> highlighted on hover) on top of it (in a sidebar, the objects' properties
>> will be listed).
>>
> Well the key there is keeping the interactive geom (query results) down to
> bare minimum size. Dont underestimate the impact of download load time (as
> opposed to interpretation in JS) on responsiveness. I am not sure
> server-side processing to canvas coordinates would be as important as
> generalizing the geometry before sending it.


One approach could be to start the download of vector geometries only after
finish rendering the WMS map. So, the user can already start reading the
map, deciding what to hover over. By that time, ((over)simplified) vectors
will nicely have been received and rendered, so the actual highlighting
will work. Thus implemented, I'm expecting a better user experience that
requiring the user to wait for 1 second again-and-again for each hovered
pixel / location.


>
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