[ka-Map-users] Optimizing map projection through changing map automatically based upon extent and scale?

[Paul Spencer]

Steve,

it would certainly be possible but it would require custom code in  
the user interface to track scale changes (there is an event emitted  
for this) and to change the map file appropriately.  I believe that  
you would want to overlap the scales such that the same scale appears  
in both maps at the point of switch over, and they should be  
essentially identical at that scale.

Cheers

Paul

On 30-Jan-07, at 12:05 PM, Steve Walker wrote:

> I have read the post and wiki about 'maintaning extents while changing
> maps,' I have a question here which could almost be re-phrased as the
> opposite:  'changing map while maintaining extents' - well almost.
>
> What I would like to do is automatically switch between map files  
> as the
> extent and scale changes.
>
> Example:  Begin with a map of the whole, which may be presented in a
> Robinson projection, or (as is most often the case) unprojected lat- 
> longs.
>
> As a user zooms in and-or pans, switch to a map which utilizes  a
> coordinate system (and perhaps different content) more appropriate  
> to the
> new extents and scale.
>
> Thus, at the scale and extent of a given country, switch to a map  
> whose
> projection is optimal (or at least appropriate) for that country;
>
> Zooming in further, switch to a map representing the appropriate  
> UTM zone;
> panning across UTM zones, seamlessly switch from one UTM map to  
> another.
>
> I can envision creating a set of invisible scale-specific, query-only
> layers which would return an 'optimal' projection and map file name  
> (the
> six-degree-wide UTM zones are easiest to visualize here) based upon a
> specific center-point-scale, then performing a coordinate  
> transformation
> on the center point xy using GEOS/PostGIS to return the transformed
> coordinates.
>
> This seems highly desirable (how many more lat-long maps must we  
> endure!?)
>
> Does this seem feasible?  Sorry I don't understand the JS code  
> enough to
> know where in the code to begin approaching the problem.
>
> -Steve
>
> -- 
> Steve Walker
> Middle Fork Geographic Information Services
> walker at mfgis.com
> 360-671-2505
>
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|Paul Spencer                          pspencer at dmsolutions.ca    |
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|Chief Technology Officer                                         |
|DM Solutions Group Inc                http://www.dmsolutions.ca/ |
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