[ka-Map-users] Switching maps, same scale

Paul Spencer pspencer at dmsolutions.ca
Thu Mar 30 08:36:01 EST 2006


its possible but requires a little bit of code to make it happen.

The first thing you need to do is intercept the call to mySetMap in  
the <select> in index.html.  You can do this by modifying the  
<select> to call your own function or my modifying mySetMap in  

I'll describe modifying mySetMap in startUp.js.  Currently this  
function reads:

function mySetMap( name ) {
     myKaMap.selectMap( name );

To get the new map to load at the same center and scale as the  
previous map, we have to pre-set the extents of the new map before  
selecting it (um, wouldn't it be nice if you could pass new extents  
or centerpoint and scale to selectMap! - I've added this to kaMap.js  
in cvs).

Looking in kaMap.js at selectMap, if the new map has a center point  
ad scale set in an array aZoomTo then it will apply it right away.   
If aZoomTo is not set, it will use the currentExtents array.  So all  
we need to do is grab the current extents or current center and scale  
and apply that to the new map before selecting it.  Center point and  
scale is more accurate since kaMap will often zoom out one scale to  
show given extents (probably a rounding error somewhere).  So the  
modified mySetMap is:

function mySetMap( name ) {
     var scale = myKaMap.getCurrentScale();
     var centerX = (extents[0] + extents[2])/2;
     var centerY = (extents[1] + extents[3])/2;
     myKaMap.aMaps[name].aZoomTo = [centerX, centerY, scale];
     myKaMap.selectMap( name );

if you are using the cvs version after my commit this morning, you  
can modify this as:

function mySetMap( name ) {
     var scale = myKaMap.getCurrentScale();
     var extents = myKaMap.getGeoExtents();
     var centerX = (extents[0] + extents[2])/2;
     var centerY = (extents[1] + extents[3])/2;
     myKaMap.selectMap( name, [centerX, centerY, scale] );



On 30-Mar-06, at 2:25 AM, Sten-Helge Henriksen wrote:

> Hi list!
> In my Ka-Map setup I have two types of maps, raster and vector,  
> which are
> covering the same geographical area.
> When I am using one map type at a low scale and want to switch over  
> to the
> other map type, I have to start all over again and manually change the
> scale to the same as on the previous map.
> Is there a way to keep those to maps at the same scale? That is  
> when the
> user switch map the same scale is maintained. And if so, how?
> Sten-Helge Henriksen
> _______________________________________________
> ka-Map-users mailing list
> ka-Map-users at lists.maptools.org
> http://lists.maptools.org/mailman/listinfo/ka-map-users

|Paul Spencer                           pspencer at dmsolutions.ca   |
|Applications & Software Development                              |
|DM Solutions Group Inc                 http://www.dmsolutions.ca/|

More information about the ka-Map-users mailing list