[Geomoose-users] Scalebar & Measure
Brent Fraser
bfraser at geoanalytic.com
Thu May 27 12:33:06 EDT 2010
In general, no; using the geodesic is preferred.
There might be some user confusion if you put a coordinate grid on the map (say
at a 10000 meter interval) and the user measures between the grid lines and gets
a value different than the grid interval. But that can be solved with
education/doc.
Brent
Dan Little wrote:
> Is there ever a reason why geodetic would be avoided (besides the compute cost in doing the math). Also, I'm vehemently against adding arbitrary parameters to the XML definition.
>
>
>
>
> ----- Original Message ----
>> From: Brent Fraser <bfraser at geoanalytic.com>
>> To: Dan Little <danlittle at yahoo.com>
>> Cc: Len Kne <lkne at houstoneng.com>; "geomoose-users at lists.sourceforge.net" <geomoose-users at lists.sourceforge.net>
>> Sent: Thu, May 27, 2010 11:11:14 AM
>> Subject: Re: [Geomoose-users] Scalebar & Measure
>>
>> How about omething like:
>
> <tool name="measure"
>> title="Measure" type="internal" action="measure"
>> geodesic="false"/>
> <tool name="measurearea" title="Measure Area"
>> type="internal" action="measurearea" geodesic="false"/>
>
> Note the
>> default would be true so the implementer would need to turn it off if they
>> wanted distances on the mapping plane.
>
>
> Hmm. Does this imply I could
>> have both geodesic AND map measures at the same time by creating these tools as
>> well:
>
> <tool name="measure2" title="Measure Ground Dist"
>> type="internal" action="measure" geodesic="true"/>
> <tool
>> name="measurearea2" title="Measure Ground Area" type="internal"
>> action="measurearea" geodesic="true"/>
>
> Brent
>
> Dan Little
>> wrote:
>> Probably just make it the default setting inside of the
>> tools.
>>
>>
>> ----- Original Message ----
>>> From:
>> Brent Fraser <
>> href="mailto:bfraser at geoanalytic.com">bfraser at geoanalytic.com>
>> To: Len Kne <
>> href="mailto:lkne at houstoneng.com">lkne at houstoneng.com>
>>> Cc:
>> "
>> href="mailto:geomoose-users at lists.sourceforge.net">geomoose-users at lists.sourceforge.net"
>> <
>> href="mailto:geomoose-users at lists.sourceforge.net">geomoose-users at lists.sourceforge.net>
>> Sent: Thu, May 27, 2010 10:02:01 AM
>>> Subject: Re: [Geomoose-users]
>> Scalebar & Measure
>>> Good.
>>
>> Should we just hard-code it within Geomoose (as below), or
>> provide a
>> configuration parameter in the mapbook?
>>
>>
>> Brent
>>
>> Len
>>> Kne wrote:
>>> Very nice!
>> Worked great and is much simpler than the way I was doing the calculation.
>>
>>> Len
>>>
>>>
>>> -----Original
>> Message-----
>>> From: Brent Fraser [mailto:
>>>
>> ymailto="mailto:
>> href="mailto:bfraser at geoanalytic.com">bfraser at geoanalytic.com"
>> href="mailto:
>> href="mailto:bfraser at geoanalytic.com">bfraser at geoanalytic.com">
>> ymailto="mailto:bfraser at geoanalytic.com"
>> href="mailto:bfraser at geoanalytic.com">bfraser at geoanalytic.com]
>> Sent: Wednesday, May 26, 2010 1:53 PM
>>> To: Len Kne
>>> Cc:
>> '
>>> ymailto="mailto:
>> ymailto="mailto:geomoose-users at lists.sourceforge.net"
>> href="mailto:geomoose-users at lists.sourceforge.net">geomoose-users at lists.sourceforge.net"
>> href="mailto:
>> href="mailto:geomoose-users at lists.sourceforge.net">geomoose-users at lists.sourceforge.net">
>> ymailto="mailto:geomoose-users at lists.sourceforge.net"
>> href="mailto:geomoose-users at lists.sourceforge.net">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:
>>>
>> href="mailto:
>> href="mailto:Paul.Wirth at kniferiver.com">Paul.Wirth at kniferiver.com">
>> ymailto="mailto:Paul.Wirth at kniferiver.com"
>> href="mailto:Paul.Wirth at kniferiver.com">Paul.Wirth at kniferiver.com]
>> *Sent:* Saturday, May 01, 2010 9:03 PM
>>>>> *To:* '
>> ymailto="mailto:
>> href="mailto:geomoose-users at lists.sourceforge.net">geomoose-users at lists.sourceforge.net"
>> href="mailto:
>> href="mailto:geomoose-users at lists.sourceforge.net">geomoose-users at lists.sourceforge.net">
>> ymailto="mailto:geomoose-users at lists.sourceforge.net"
>> href="mailto:geomoose-users at lists.sourceforge.net">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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