[Geomoose-users] Scalebar & Measure

[Brent Fraser]

Paul, Len,

   Our scale problem is a (mostly) map projection issue.  All map projections 
introduce distortions in trying to represent a round(ish) Earth on a flat plane. 
  Mercator is no different: it is like wrapping an up-right cylinder around the 
Earth, projecting light from the center onto the cylinder 
(http://en.wikipedia.org/wiki/Mercator_projection).  As you can imagine the 
distortions get "worse" the further from the equator.   The distortions can be 
modeled as a Point Scale Factor.  At the equator the Point Scale Factor is 1.0, 
at latitude 60 degrees North (or South), the scale factor is 0.5!

   So what's the solution?  Here's mine:

   1. Enhance Proj4 (and Proj4js) to return the Point Scale factor (given the 
projection and a location)
   2. Enhance MapServer and Openlayers to use the Point Scale Factor in 
calculating distances and scale.

I'm trying to drum up interest, but so no takers....
   http://osgeo-org.1803224.n2.nabble.com/Point-Scale-factor-service-td4938743.html
 
http://osgeo-org.1803224.n2.nabble.com/Re-3265-Scale-dependent-layer-switching-error-with-Mercator-td4966902.html

Best Regards,
Brent Fraser

Len Kne wrote:
> The scale bar issue with the web Mercator projection is a limitation of 
> OpenLayers, the application GeoMOOSE 2.x uses to render the map frame. 
>   There has been discussion on the OpenLayers site about providing a 
> patch (this link offers a patch http://trac.openlayers.org/ticket/1890 ) 
> in the next version 2.9.  I’m sure GM will upgrade to OL 2.9, but not 
> sure there is any schedule in place to do this.
> 
>  
> 
> The cursor issue is also kind of fun because it seems each browser 
> handles the custom icons differently.  Here’s the attribute in the 
> mapbook which defines the query for the Identify service:
> 
>  
> 
> cursor="url('cursors/identify2.cur') 9 9,url('cursors/identify2.cur'),auto"
> 
>  
> 
> This makes three attempts to draw the cursor, the first offsets the 
> mouse click 9 pixels from the top and the left.  Firefox can use this 
> value and seems to line the mouse click up pretty good with the 
> crosshair.  However, IE cannot handle the offset adjustment, so it reads 
> the second cursor definition.  There are tools like AT File Mole which 
> can be used to edit the hotspot of a cursor.  Attached is the latest 
> version I have been using for Identify service, again this seems to line 
> the crosshair up pretty well with the mouse click.  If you are using 
> Safari or Chrome, these setting don’t seem to work at all and I would 
> recommend not using customer cursors with those browsers.
> 
>  
> 
> Len
> 
>  
> 
> *From:* Wirth, Paul [mailto:Paul.Wirth at kniferiver.com]
> *Sent:* Saturday, May 01, 2010 9:03 PM
> *To:* 'geomoose-users at lists.sourceforge.net'
> *Subject:* [Geomoose-users] Scalebar & Measure
> 
>  
> 
> Two questions:
> 
>  
> 
> 1.       I have a web Mercator application, and I noticed that the 
> scalebar does not display the correct distance.  For instance, when the 
> scalebar shows a distance of 20 miles, it measures only 13.8 miles.  I 
> know the measure tools are working correctly, so I assume this is a 
> scalebar issue.  Any thoughts on how to fix this?
> 
> 2.       I think this question was asked before, but I can’t seem to 
> find it on the e-mail list.  With the measure tools, the cursor does not 
> start measuring at the “crosshairs” when the user clicks, but rather in 
> the NW quadrant of the crosshairs.  Is there a way to change it so the 
> measure start point will be on the crosshairs?
> 
> 
> ------------------------------------------------------------------------
> 
> ------------------------------------------------------------------------------
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> Geomoose-users mailing list
> Geomoose-users at lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/geomoose-users