[OpenLayers-Dev] Design for scale-line

[Ian Mayo]

thanks for the support Paul.

and I thought I was sooo close.  Yet more details of OpenLayers
projections to learn....  Thanks for the pointers anyway,

regards,
Ian.

On 05/10/2007, Paul Spencer <pspencer at dmsolutions.ca> wrote:
> Hi Ian,
>
> looks like nicely written code :)  I'm sure this will be very useful
> to have as a Control in OpenLayers.  I have a few comments:
>
> 1) you have a problem with tabs vs spaces in code formatting that
> made my eyes wonky in a couple of places.
>
> 2) you do not seem to be accommodating the current units of the map -
> I use different projections, often in meters.  From the docs:
>
> units
>
> {String} The map units.  Defaults to 'degrees'.  Possible values are
> 'degrees' (or 'dd'), 'm', 'ft', 'km', 'mi', 'inches'.
>
> So you need to check to see what map.units is before converting
>
> 3) If the units are decimal degrees, you should adjust the
> calculation based on the current latitude of the center using the
> cosine of the latitude.  This was from a distance measuring tool I
> did a while back:
>
> d = d * Math.cos(2 * Math.PI * map.center.lat / 360);
>
> 4) you will need to accomodate the spherical mercator stuff too ...
> loads of people use that
>
> Cheers
>
> Paul
>
> On 5-Oct-07, at 10:22 AM, Ian Mayo wrote:
>
> > Hi all, I have a working demonstrator at:
> > http://dev.openlayers.org/sandbox/ianmayo/openlayers/examples/
> > controls.html
> >
> > At the top-right of the plot you'll see the current scale represented
> > as a bar.  As far as I can see, the implementation seems sound - I
> > just have to polish off the unit tests (the earlier tests were more
> > associated with me learning how the scaling works).
> >
> > Aaah, and yes, please break it & report as appropriate.  I'd also
> > appreciate hearing what configurable options people may want.
> > Currently we have m/km on the top and ft/mi on the bottom - switching
> > between the correct set to use depending on how far we've zoomed in.
> > Does anybody want to be able to configure to use other units?
> >
> > Ian.
> >
> > On 02/10/2007, Ian Mayo <ian at planetmayo.com> wrote:
> >> Here's the design for my OpenLayers scale control, aimed to offer
> >> similar functionality to the scale offered in google maps.
> >> Any advice?
> >>
> >> thanks in advance for any support,
> >> Ian.
> >>
> >> p.s.  Should I have written this content into a wiki page?
> >> Opinions welcome.
> >>
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>
> +-----------------------------------------------------------------+
> |Paul Spencer                          pspencer at dmsolutions.ca    |
> +-----------------------------------------------------------------+
> |Chief Technology Officer                                         |
> |DM Solutions Group Inc                http://www.dmsolutions.ca/ |
> +-----------------------------------------------------------------+
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