scale problem

[Steve Lime]

Scalebar computations will not be particularly accurate with unprojected output
for the reason Simon mentions. For projected output the scalebars produced are
quite good. Since they are raster images they are prone to a bit of rounding error
as the line work is drawn.

Comparisons between the scalebar images and features drawn on the screen are
very sensitive to how your are computing cellsize. MapServer uses a cell center to
cell center pixel model with an extent running from the center of the UL cell to the
center of the LR cell.

Steve

>>> On 10/31/2007 at 4:46 PM, in message <4728F7BD.1050206 at sibern.com.au>, Simon
Haddon <simon at SIBERN.COM.AU> wrote:
> Hi Giuseppe,
> 
> I have a scalebar problem too.  In my case I can draw polygons and lines 
> on the screen which do not even come close to the scalebar depending 
> where in Australia I am.  I know my drawing tools and the distance 
> measurement toos are accurate but the mapserver scalebar is not.
> 
> Looking into the code I discover that the scalebar is only calculated on 
> the equator when using geographics.  This might be related to what you 
> are seeing depending where on the planet you are.  The other problem is 
> related to the project being used and the area.  Since you are dealing 
> in millimeters it could be a real problem.
> 
> I have thought replacing the mapserver created scalebar with a 
> javascript created scale bar or looking at how the scalebar is created 
> and try to make it more accurate.
> 
> Any suggestions anyone
> 
> Cheers,
> Simon Haddon
> 
> Giuseppe De Rossi wrote:
>> Hi 
>> (sorry if this is a repost for you)
>> I've pointed that when
>> I put the scale to 1000 (or 1/1000), in the map 1 mm should be egual to 1
>> meter, well, if I print the map and I try to measure it by using a real
>> meter line I see that the map is stretched.
>> I don't know if it is only my experence. Please, try to print a Map after
>> setting the scale to a normalized value as for example 1/1000, now on your
>> paper try to measure a distance by using a line: the number of n millimeters
>> should correspond to n meters, but the line will measure a different number
>> of millimeters.
>> Is that your experience too ? is there anybody who can explain me this item,
>> and is there solution in order to have a phisical millimeter on the paper
>> when I set the scale to 1/1000 ?
>>
>> Another issue: how can I get the meter (graphical) line under the main map
>> to have normalized values as factor of 10 ie 10,10... 100 meters etc ?
>> The target consists on using the map as a valid measurement tool.
>>
>>
>> thaks to everybody
>>  
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