[Geomoose-users] Possible Bug / Issue with the scale - geomoose 2.2?

[Brent Fraser]

That does sound like a bug.  Does it exist in v2.4?

Best Regards,
Brent Fraser


On 1/12/2012 2:33 PM, Mark Volz wrote:
>
> Brent,
>
> I found that measuring on screen works fine, however I agree with you 
> it is not a good idea.  The issue that I am having is that the 
> reported scale on the scale drop down list located at the bottom of 
> the screen appears to be incorrect when compared to the measuring 
> tools, or Arcgis.  For example the scale 1:864 on GeoMOOSE appears to 
> be the same scale as 1:1200 on ArcMap, and when I measure 1 foot on 
> the screen in either application I get 1200 feet.  Long story short, I 
> think that the scale text on the dropdown menu is only 72% as large as 
> it should be.   That's why I think it is a bug, but in either case I 
> am not going to push the issue any further.
>
> Mark Volz
>
> GIS Specialist
>
> *From:*Brent Fraser [mailto:bfraser at geoanalytic.com]
> *Sent:* Thursday, January 12, 2012 2:56 PM
> *To:* Mark Volz
> *Cc:* GeoMOOSE Users List
> *Subject:* Re: [Geomoose-users] Possible Bug / Issue with the scale - 
> geomoose 2.2?
>
> Mark,
>
>   The glib answer is "don't measure on the screen".  Now for the long 
> answer....
>
>   I did an evaluation of the scale in GeoMoose v1.6.1 a couple of 
> years ago and found the same problem as you.  Back then (before 
> OpenLayers), there was a GeoMoose config setting called 
> MAP_PIXELS_PER_INCH with a default setting of 72.  When I adjusted it 
> to my screen's dpi the scale was fine.  I expect there is a similar 
> setting in OpenLayers (DOTS_PER_INCH?).  But the problem is you can't 
> depend on a monitor having a particular dpi (the browser can look it 
> up though).  Here's some of the chatter from Sept 2009 (it that email 
> archived somewhere?):
>
>
>   I'm not really too concerned about the map scale on the screen,
> but I wanted to make sure I understood how Mapserver/Geommoose/FPDF was scaling
> the images (since the printed scale is very important).
>   
> So the first step is to get the screen scale close:
>   
>     Measuring the boxes in the link you provided below (https://gis.ci.stpaul.mn.us/10in-test.html), I saw that they were 5%
> too big (the 10cm box measured 10.5cm).  I looked up the "pixel pitch" of my
> monitor (0.281 mm/pixel), calculated the dpi (90.391), set that value (it was
> originally set to 96 dpi) in the Display (Control
> panel->display->settings->advanced->general), rebooted. ... Perfect!
>   
>     Now to measure my graticule.  With "MAP_PIXELS_PER_INCH = 72" in the Geomoose
> config.js file, the grid spacing was about 20% too small; not good.  I changed
> my site settings from "MAP_PIXELS_PER_INCH = 72" to MAP_PIXELS_PER_INCH =
> 90.391; ... Perfect!
>   
>   
> The bottom line is, while most (all?) monitor drivers dpi setting may be off,
> Geomoose would be better off doing the calculation as Bob pointed out below,
> rather than "hard-coding" it in the site settings.
>   
>     Now I need to look at the printed map scale process...
>
> ==================================================================
>
>     To sum up:
>   
> 1. Printing to Scale
> --------------------
>     I made some mods to v1.6.1 to pass the value of the ScaleBox to the PHP
> printing system, and added some code to re-calc the extents of the map portion
> of the page.   It seems to work well.  If others are interested, I can talk with
> Dan to get the changes integrated into geomoose-trunk (AKA v1.6.1+).   Some
> parts may even be useful for GM v2.
>   
> 2. Map to Scale on the Screen
> -----------------------------
>     There's no need to adjust your display driver DPI setting, just set the
> MAP_PIXELS_PER_INCH value in Geomoose's config.js and you'll get a map displayed
> exactly to scale.  However, this value will be used for all client screens (and
> they likely all have different DPI), so unless one of your users complains,
> don't bother.
>   
> 3. Better Screen Scale
> ----------------------
>     A low priority enhancement for GM v2 would be to have the JavaScript
> calculate the screen resolution (see Bob's earlier posting in this thread) to
> get the screen scale to within 5%-ish (instead of the current 20% to 30%).
>
>
>
>
> Best Regards,
> Brent Fraser
>
>
> On 1/12/2012 12:47 PM, Mark Volz wrote:
>
> Hello,
>
> I noticed that the text on the scale dropdown is incorrect.  For 
> example, I measured 1 foot on my screen, which measured out to be 1200 
> feet on the map; which works out to be a scale of 1:1200.  The stated 
> scale on the textbox on the bottom of the screen reported that the 
> scale is 1:864 not 1:1200, which it should be.  I noticed that 
> 864/1200 is .72, which mapserver assumes a 72 DPI, so I don't know if 
> that has something to do with the scale being incorrect.
>
> This bug / issue is on all of many of the 2.2 sites that I are out there.
>
> Thanks
>
> Mark Volz
>
> GIS Specialist
>
>
>
>
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