[OpenLayers-Dev] Design for scale-line

Lorenzo Becchi lorenzo at ominiverdi.com
Tue Oct 2 18:15:18 EDT 2007

Ian, have you ever seen Tim Schaub's Scalebar for ka-Map?
that's all JS and CSS:


Ian Mayo wrote:
> Here's the design for my OpenLayers scale control, aimed to offer
> similar functionality to the scale offered in google maps.
> The new control is to be called "ScaleLine".  Yes, there's lots of
> room for improvement there, suggestions welcome.
> Here are the steps I'll take:
> 1. Determine current scale
> 2. Determine width of view in metres
> 3. Determine how wide 10% of view is in metres
> 4. Round width up/down to nearest "round number" in increasing size of units:
>    -- 1,2,5,10,20,50,100,200,500 (metres)
>    -- 1,2,5,10,20,50,100,200,500,1000,2000 (km)
> 5. Calculate size of line of rounded length in screen units
> 6. Draw line of scaled length, with text-label on right-hand size into
> 'div' for this control
> 7. Repeat the above for imperial units
> The Div will have been located using the css-style called .olControlScaleLine
> Questions from me?
> Well, yes.  I've seen from the other controls how to draw plain text
> onto the map.  Drawing my graphic is a little more complex.  Should
> the line and "tails" be an OpenLayer feature?  Or is there another
> method for drawing line-based items.  I suppose I could have a div
> with left, bottom, right borders - with the div-width set to the width
> in step 5 above.
> 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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