[Geomoose-users] Scalebar & Measure

[Len Kne]

Very nice!  Worked great and is much simpler than the way I was doing the calculation.  

Len

-----Original Message-----
From: Brent Fraser [mailto:bfraser at geoanalytic.com] 
Sent: Wednesday, May 26, 2010 1:53 PM
To: Len Kne
Cc: 'geomoose-users at lists.sourceforge.net'
Subject: Re: [Geomoose-users] Scalebar & Measure

Len(and others interested in measuring),

   Here's my solution to the measure problem:

In main.js somewhere around line 138 add the two lines below marked with a "//BWF":

	Tools['measure'] = new 
OpenLayers.Control.GeoMooseMeasure(OpenLayers.Handler.MeasurePath, 
measureToolOptions);
	Tools['measure'].geodesic = true;  //BWF

	Tools['measurearea'] = new 
OpenLayers.Control.GeoMooseMeasure(OpenLayers.Handler.MeasurePolygon, 
measureToolOptions);
	Tools['measurearea'].geodesic = true;  //BWF

Thoughts?

Brent


Brent Fraser wrote:
> 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?
>>
>>
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