Re: [Mapbuilder-devel] 7-parameter datum transformation bug in Proj4js

[Mike A. <ma...@dm...>]

Andreas,

I've been looking into this and I think there is a problem with the 
Google CS and the datum transformation (Richard and Frank - please feel 
free to jump in here and set me straight).  The Google projection 
doesn't really define a datum from what I can gather so I think it's 
invalid to try and do a datum shift with it.  The datum shift for 
EPSG:31285 going to/from WGS84 seems to work without a problem.

So what I've done in proj4js is to allow a 'datum=none' parameter (and 
added that to the Google def string) which will bypass the datum 
transformation if it is set for either source or destination coordinate 
system.  From my test cases, I'm still seeing differences on the order 
of 100m in the y value and I'm wondering if that's the best we can do in 
this case.

It's probably too late to get this into mapbuilder RC1, but it is set to 
go for RC2.  The updated proj4js files are at: 
https://svn.codehaus.org/mapbuilder/cscs/trunk/proj4js/lib.  Please try 
it out and let me know how it works for you.

Mike

Mike Adair wrote:
> Andreas,
>
> Since we are still using the mapbuilder SVN for proj4js, I think it's 
> best to use the mapbuilder JIRA for bug reports.  I've added a 'proj4js' 
> component for that so they can be assigned to that component until there 
> is a project of it's own for projection related stuff.
>
> For this specific issue, you should definitely be using the toWGS84 
> parameters but I'm not sure why it doesn't work going to 900913.  The 
> test case for it that I have going to and from WGS84 is accurate within 
> about 5mm.  However comparing Proj4 and Proj4js code now for the 
> mercator projection, I'm seeing some differences and the the lat_ts 
> parameter isn't supported.  I'll have a look into that ASAP.
>
> Mike
>
> Andreas Hocevar wrote:
>   
>> Hi,
>>
>> first of all, which is the preferred way of reporting bugs for
>> Proj4js? Because I do not know better, here is a bug report.
>>
>> Recently, I created the new mergeModels example in Mapbuilder trunk.
>> For this example, I have data in EPSG:31285. There is a proj def file
>> for that projection in Mapbuilder trunk, but it is not the latest
>> version of the proj4 definition. The latest version, which is already
>> online at spatialreference.org, contains +toWGS84 parameters for a
>> 7-parameter transformation. But if I use this new version, the
>> conversion to EPSG:900913 results in coordinates that are several km
>> shifted to south.
>>
>> This can easily be tested with the mergeModels examples, when the proj
>> def is updated with the transformation parameters.
>>
>> Mike, it would be great if you could investigate/fix this.
>>
>> Thanks!
>> Andreas.
>>
>>   
>>     
>
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