[MetaCRS] proj4js and axis order

[Bart van den Eijnden (OSGIS)]

Indeed, thanks for the detailed explanation Chris.

So there are no plans to extend the proj4js projection object with this 
info? That will make it really hard to make a generic WMS 1.3 javascript 
client ..... maybe I can take a shot at it with a few pointers.

Chris, can the axis order info be retrieved through 
spatialreference.org, and if so, how? TIA.

Best regards,
Bart

Christopher Schmidt wrote:
> On Wed, Sep 30, 2009 at 09:11:01AM -1000, Harley Powers Parks wrote:
>   
>> Hi, just curious.
>>
>> What is meant by "axis order"?
>>
>> Axis orientation from the origin..0,0 on a 2D plane? X is horizontal,
>> increase from left to right, decreases from right to left; y is vertical
>> perpendicular to X axis, increase from low to high, decreases from high to
>> low.
>>     
>
> Axis order, as it relates to coordinate systems, is the definition of 
> which axis comes first in a series of coordinates. So, for example, if you
> have Boston, is the point:
>   
>  * lon, lat -- -71, 42
>  * lat, lon -- 42, -71
>  * x, y,   y, x,  x, y, z, etc.
>
> The EPSG database defines, for each projection, the order of the coordinates
> within a set of coordinates. Generally, these coordinates are lat, lon
> ordered in the case of geographic projections, and lon, lat ordered in the
> case of projected coordinate systems.
>
> However, there are exceptions to all of these cases.
>
> More modern WMS specs require clients to know what the coordinate order 
> for a set of coordinates is, and request a bounding box (4-tuple defining
> a 2d box) in that projection. So for Boston, you have to request in
>   
>   srs=EPSG:4326&bbox=41,-72,43,-70
>
> The problem with this is, of course, the fact that in order to make this 
> request correctly, rather than assuming you can just do 'min_x, min_y, 
> max_x, max_y', you have to have a complete knowledge of the coordinate 
> systems that are possible to use in your application, or have some way
> to communicate or obtain that data.
>
> Best Regards,
>   


-- 
Bart van den Eijnden
OSGIS, Open Source GIS
bartvde at osgis.nl
http://www.osgis.nl