[mapserver-users] PHP Mapscript delivers map with larger extent than requested

[Moen, Paul T.]

Where are you setting the map size?

$map->setSize($pwide,$ptall);

You may need to set the size of the map before you set the extents.

Paul

On Oct 26, 2009, at 11:44 AM, Chuck Jungmann wrote:

> I am using MapScript with PHP because I want to be able to request a  
> map
> with a url, change the content-type and send saveImage directly to
> STDOUT.
>
> An example (relative) URL:
> map.php?lat=42.056542&lon=-88.035765&ext=300&pwide=500&ptall=500
>
> Where "ext" is the width, in meters, on the ground (difference in
> longitude), "ptall" and "pwide" are the pixel dimensions of the  
> desired
> map bitmap.  If my server returns the map image I request, I can have
> the client calculate the coordinates of any pixel on the map image
> without having to bother the server.
>
> The server uses pwide/ptall and ext to determine difference in  
> latitude,
> then the corners of the rectangle for MapObj::setextent().
>
> Before I got your response, I was doing everything in lat/lon
> coordinates, but something in your note made me realize that I should
> use the native projection which is in meters for fewer calculations  
> and
> an easier set of numbers to check the output.
>
> Here is the stripped-out code (functions merged, error-checking
> removed):
>
> // load a minimal map, add layer with specific map:
> $map = ms_newMapObj("/mapdata/minmap.map");
> $map->setProjection("init=epsg:26916");
> $lay = ms_newLayerObj($map);
> $lay->set("name", "tempRaster");
> $lay->set("status", MS_ON);
> $lay->set("type", MS_LAYER_RASTER);
> $lay->set("data", "taxmap.tif");
> $lay->setProjection("init=epsg:26916");
>
> // projection objects for converting point
> $projlatlon = ms_newprojectionobj("proj=latlong");
> $proj26916 = ms_newprojectionobj("init=epsg:26916");
>
> $pt = ms_newPointObj();
> $pt->setXY($lon,$lat);
> $pt->project($projlatlon, $proj26916);
>
> $halfTall = $ext * $pwide / $ptall / 2;
> $halfWide = $ext / 2;
>
> $map->setextent($pt->x-$halfWide, $pt->y-$halfTall, $pt->x+$halfWide,
> $pt->y+$halfTall);
>
> Given the example above, the extent values I use are:
> 414145.897891, 4656422.994605, 414445.897891, 4656722.994605,
> exactly 300 meters X and Y.
>
> Immediately after $map->setextent(), I look at the values of
> $map->extent and the values are:
> 414095.793507, 4656422.994605, 414496.002275, 4656722.994605
> the differences are 400.21 X, 300 Y.  4/3 is familiar as screen ratio,
> but I don't see why that would apply here.
>
> Here is the .tfw file for the map (confirming square pixels):
> 0.205001999999928690
> 0.0
> 0.0
> -0.205001999999928690
> 413698.77641943324
> 4656861.2550850855
>
> Thanks for your response.  I apologize for not including all this
> information in my first note, but too many times I have spent a lot of
> time writing a note like this only to get no responses.
>
> Chuck Jungmann
>
>
>
>
>
> My MapServer version info:
> MapServer version 5.0.3 OUTPUT=GIF OUTPUT=PNG OUTPUT=JPEG OUTPUT=WBMP
> OUTPUT=SVG SUPPORTS=PROJ SUPPORTS=AGG SUPPORTS=FREETYPE
> SUPPORTS=WMS_SERVER SUPPORTS=WMS_CLIENT SUPPORTS=WFS_SERVER
> SUPPORTS=WFS_CLIENT SUPPORTS=WCS_SERVER SUPPORTS=FASTCGI
> SUPPORTS=THREADS SUPPORTS=GEOS INPUT=EPPL7 INPUT=POSTGIS INPUT=OGR
> INPUT=GDAL INPUT=SHAPEFILE
>
>
>
> On Sun, 2009-10-25 at 01:06 -0400, Stephen Woodbridge wrote:
>> Chuck Jungmann wrote:
>>> I am a new user of MapServer, using version 5.0.3 from the Ubuntu
>>> repositories.  I attempted to compile everything from source, had  
>>> some
>>> trouble, then decided to use the repository shortcut at least  
>>> until I
>>> understood how the application works.
>>>
>>> I am writing an application where the browser requests a map by  
>>> setting
>>> the src attribute of an img object.  Identifying locations on the
>>> resulting map requires that the application knows the extent.
>>>
>>> I calculate the extent of the map from various values, and use the  
>>> same
>>> algorithms on the server so the browser and the server agree on the
>>> dimensions without having to negotiate.  However, when I request  
>>> the map
>>> from MapServer, the extent of the resulting map is always larger  
>>> (both x
>>> and y dimensions) than what I requested, although still centered  
>>> on the
>>> same point.
>>>
>>> Is this behavior normal (I don't want to beat my head against the  
>>> wall
>>> searching for an irrelevant math error)?  Is there some setting that
>>> might cause MapServer to more closely match my requested extent?   
>>> Could
>>> this be an error that was fixed in a more recent version of  
>>> MapServer?
>>>
>>> Any words of wisdom would be appreciated.
>>
>> Chuck,
>>
>> There are a number of conditions that may make mapserver checnge the
>> extents requested.
>>
>> 1) mapserver assumes square pixels, so if you ask for an extents that
>> has a different aspect ratio than that of you image size then  
>> mapserver
>> will make adjusts.
>>
>> 2) if you ask for extents and a scale, I think, mapserver will use  
>> the
>> extents to determine the center and then adjust the extents to the  
>> scale
>>
>> Are you using the CGI interface? what does you request look like? You
>> need to give us more concrete examples that we can try here to test  
>> out
>> and explain what is happening. What version of mapserver are you  
>> using?
>>
>> /path/to/mapserv -v
>>
>> Will report how it was build with options and version number.
>>
>> -Steve W.
>>
>
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