Fwd: [MAPSERVER-USERS] Problems calculating MAXSCALES

[Daniel Morissette]

Glad to hear that Trac prevents reopening closed tickets by default. 
This is not a bad thing since that ticket was closed in a previous 
release and reopening tickets usually leads to confusion.

I'd suggest you open a new ticket and refer to the original one that you 
were trying to reopen.

Daniel


Rob wrote:
> Sorry - didnt reply to whole list
> 
> 
> ---------- Forwarded message ----------
> From: Rob <gis at vanbooth.com>
> Date: 2008/8/13
> Subject: Re: [MAPSERVER-USERS] Problems calculating MAXSCALES
> To: Tamas Szekeres <szekerest at gmail.com>
> 
> 
> I was unable to reopen the ticket with comments - "TICKET_APPEND
> privileges are required to perform this operation"
> 
> If someone else could reopen on my behalf, this is what I wrote for
> the comments -
> 
> I've recently updated from 4.8.6 to 5.0.2 and fallen foul of this
> defect, where layers are not visible when I would expect them to be.
> 
> I'm in OSGB Projection (epsg:27700) but I didn't include this
> information in my sample mapfiles, in case it was a projection related
> issue.  My implementation uses mapscript rather than the cgi mapserv
> process, but I have been testing using shp2img.
> 
> 4.8.3 Mapfile
> 
> {{{
> MAP
>  EXTENT 200000 200000 266145 266145
>  IMAGECOLOR 255 255 255
>  IMAGETYPE png
>  RESOLUTION 96.000000
>  SIZE 500 500
>  STATUS ON
>  TRANSPARENT TRUE
>  UNITS METERS
>  NAME "Base"
>  IMAGEQUALITY 75
> 
>  LEGEND
>    IMAGECOLOR 255 255 255
>    KEYSIZE 20 10
>    KEYSPACING 5 5
>    LABEL
>      SIZE MEDIUM
>      TYPE BITMAP
>      BUFFER 0
>      COLOR 0 0 0
>      FORCE FALSE
>      MINDISTANCE -1
>      MINFEATURESIZE -1
>      OFFSET 0 0
>      PARTIALS TRUE
>    END
>    POSITION LL
>    STATUS OFF
>  END
>  WEB
>    IMAGEPATH "c:\tmp\"
>    IMAGEURL "/"
>    QUERYFORMAT text/html
>    LEGENDFORMAT text/html
>    BROWSEFORMAT text/html
>  END
>  LAYER
>    MAXSCALE 500000
>    MINSCALE 0
>    NAME "Land"
>    STATUS ON
>    TRANSPARENCY 100
>    TYPE RASTER
>    UNITS METERS
>    DATA "C:\Documents and Settings\Administrator\Desktop\gb\gbpng.tif"
>  END
> END
> }}}
> 
> 
> 5.0.2 Mapfile
> 
> {{{
> MAP
>  EXTENT 200000 200000 266145 266145
>  IMAGECOLOR 255 255 255
>  IMAGETYPE png
>  RESOLUTION 96.000000
>  SIZE 500 500
>  STATUS ON
>  TRANSPARENT TRUE
>  UNITS METERS
>  NAME "Base"
>  OUTPUTFORMAT
>    NAME "png"
>    MIMETYPE "image/png"
>    DRIVER "GD/PNG"
>    EXTENSION "png"
>    IMAGEMODE "PC256"
>    TRANSPARENT TRUE
>  END
>  PROJECTION
>    "init=epsg:27700"
>  END
>  LEGEND
>    IMAGECOLOR 255 255 255
>    KEYSIZE 20 10
>    KEYSPACING 5 5
>    LABEL
>      SIZE MEDIUM
>      TYPE BITMAP
>      BUFFER 0
>      COLOR 0 0 0
>      FORCE FALSE
>      MINDISTANCE -1
>      MINFEATURESIZE -1
>      OFFSET 0 0
>      PARTIALS TRUE
>    END
>    POSITION LL
>    STATUS OFF
>  END
>  WEB
>    IMAGEPATH "c:\tmp\"
>    IMAGEURL "/"
>    QUERYFORMAT text/html
>    LEGENDFORMAT text/html
>    BROWSEFORMAT text/html
>  END
>  LAYER
>    DEBUG 5
>    MAXSCALEDENOM 500000
>    MINSCALEDENOM 0
>    NAME "Land"
>    STATUS ON
>    TRANSPARENCY 100
>    TYPE RASTER
>    UNITS METERS
>    DATA "C:\Documents and Settings\Administrator\Desktop\gb\gbpng.tif"
>  END
> END
> }}}
> 
> GBPNG.TFW
> 
> {{{
> 333.333333333
> 0.000
> 0.000
> -333.333333333
> 166.66666666
> 649833.33333333
> }}}
> 
> Any 1000x1000 image should work.
> 
> Running shp2img against 4.8.3 will produce a valid image.  Running
> shp2img against 5.0.2 does not.
> 
> Code is currently
> 
> 
> {{{
> center_y = (extent.miny+extent.maxy)/2.0;
>   md = (width-1)/(resolution*msInchesPerUnit(units, center_y)); /*
> remember, we use a pixel-center to pixel-center extent, hence the
> width-1 */
>   gd = extent.maxx - extent.minx;
>   *scale = gd/md;
> }}}
> 
> For the extents in the mapfiles, this gives a scale of 500997
> 
> Previously, using (width) instead of (width-1), we would have had 499993
> 
> My desktop GIS product seems to agree with the calculation to result
> in 499993, judging by the bbox it requests when zooming to 1:500,000
> 
> Full mapserver-users conversation is here -
> http://www.nabble.com/Problems-calculating-MAXSCALES-td18926188.html
> _______________________________________________
> mapserver-users mailing list
> mapserver-users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-users


-- 
Daniel Morissette
http://www.mapgears.com/