Mapscript Re-Projection : Calculating zooms

[Stefan Schwarzer]

Hmm, sorry to show up again here.

I am not too sure how to handle the following request(s) (by the same  
user):

	1) the first map in the browser shows up in the original projection,  
i.e. geographic
	2) now the user changes to say Mollweide, and request a redraw of  
the map
	3) the reprojection is being done in the background via the two  
lines mentioned below,
	     the map displayed in the browser now in global view and  
Mollweide projection
	4) the user now makes a second request - either adding a layer or by  
zooming in

So, now the incoming extent coordinates (imgext) are like this:

	-18040095.70 -9020047.85 18040095.70 9020047.85

instead of

	-180 -90 180 90

I have now the possibility to
	- calculate the values (in meter) back into DD
	- do the zoom in
	- and project the map again into Mollweide

I probably would use something like this

	$mollweide=ms_newprojectionObj("proj=moll,lon_0=0,x_0=0,y_0=0" );
	$newproj = ms_newprojectionObj 
("proj=longlat,ellps=WGS84,datum=WGS84,no_defs" );
	$oRect= ms_newRectObj();
	$oRect->setextent(-18040095.70, -9020047.85, 18040095.70, 9020047.85);
	$oRect->project($mollweide,$newproj);
	$map->setextent( $oRect->minx, $oRect->miny, $oRect->maxx, $oRect- 
 >maxy );

	and then reproject it again into Mollweide?

Seems rather "cumbersome"....

Stefan


> Jacob, Nicol,
>
> Ahhhh.... bit irritating these different coding possibilities...
>
> Ok, I met the original definition to all layers AND the map file:
> 	
> 	PROJECTION
> 		'init=epsg:4326'
> 	END
>
> and when using
>
> 	$newproj="proj=robin,lon_0=0,x_0=0,y_0=0"; // projection string of  
> your new projection
> 	$map->setProjection($newproj,MS_TRUE);
>
> it indeed works!
>
> Great, thanks a lot guys for that help!!!
>
> Best regards,
>
> Stef
> 	
>
>
> On Aug 24, 2006, at 10:05 AM, Delfos, Jacob wrote:
>
>> Hi Stefan,
>>
>> Yes, you do have to specify which projection each layer is in,  
>> otherwise when they are reprojected you will run into trouble (if  
>> it doesn't know where to reproject FROM, it won't be able to do  
>> i). It's not too hard, though.
>>
>> You should not have to recalculate the extent; it should be  
>> automatic. Definitely don't try to change the numbers  
>> (coordinates) without changing the projection (that would be bad).
>>
>> Try this:
>>
>> $newproj="proj=robin,lon_0=0,x_0=0,y_0=0"; // projection string of  
>> your new projection
>> $map->setProjection($newproj,MS_TRUE);
>>
>> I think that ought to be all.  The MS_TRUE makes it pick the best  
>> fit to the current extent in the new projection. Make sure your  
>> projection string is valid.
>>
>> regards,
>>
>> Jacob
>>
>>
>>
>> From: UMN MapServer Users List [mailto:MAPSERVER- 
>> USERS at LISTS.UMN.EDU] On Behalf Of Stefan Schwarzer
>> Sent: 24 August 2006 15:35
>> To: MAPSERVER-USERS at LISTS.UMN.EDU
>> Subject: Re: [UMN_MAPSERVER-USERS] Mapscript Re-Projection on-the-fly
>>
>> Jacob & Nicol,
>>
>> thanks for your feedback.
>>
>> But I am still struggling. Just to clarify: I wonna reproject not  
>> individual layers, but my whole map.
>>
>> Jacob, does "For this, it is required that your layer has a  
>> projection object with the native projection of that layer." that  
>> mean that for each single layer I have to specify the original  
>> projection? (Geographic in my case)
>>
>> As Nicol stated I need to "recalculate" the extent, at least when  
>> using different units (going from DD to Meters).
>>
>> But then, I found that piece of code (slightly changed):
>>
>> $newproj=ms_newprojectionObj("proj=robin,lon_0=0,x_0=0,y_0=0");
>> $latlon=ms_newprojectionObj 
>> ("proj=longlat,ellps=WGS84,datum=WGS84,no_defs");
>> $oldext=ms_newRectObj();
>> $oldext->setextent(-180,-90,180,90);  //this is the extent of my  
>> map in geographic
>> $oldext->project($latlon,$newproj);  //reproject to Robinson
>> $map->setextent($oldext->minx,$oldext->miny,$oldext->maxx,$oldext- 
>> >maxy);  //set the new map extent
>>
>> And another one going like this:
>>
>> $projInObj = ms_newProjectionObj( "+proj=tmerc ".
>>   "+lat_0=49 ".
>>   "+lon_0=-2 ".
>>   "+k=0.999601 ".
>>   "+x_0=400000 ".
>>   "+y_0=-100000 ".
>>   "+ellps=airy ".
>>   "+towgs84=375,-111,431,0,0,0,0");
>>
>> with this info in the mapscript documentation...
>>  int setProjection(string proj_params, boolean bSetUnitsAndExtents)
>>         Set map projection and coordinate system.  Parameters are  
>> given as
>>         a single string of comma-delimited PROJ.4 parameters.
>>         The argument : bSetUnitsAndExtents is used to  
>> automatically update
>>         the map units and extents based on the new projection.  
>> Possible
>>         values are MS_TRUE and MS_FALSE. By defualt it is set at  
>> MS_FALSE
>>
>> So, what should I use? And where is coming the
>>
>> $map -> setProjection
>>
>> into play?
>>
>> Thanks for any clarification.
>>
>> Stefan
>>
>>
>>
>> On Aug 24, 2006, at 7:59 AM, Delfos, Jacob wrote:
>>
>>> Stefan,
>>>
>>> Your question is not entirely clear. You can not re-project an  
>>> individual layer on-the-fly, because php_mapscript does not re- 
>>> write the dataset (hence its projection will always be the same);  
>>> you CAN however change the projection of the map (using  
>>> setProjection, as you did), which means all layers in the map get  
>>> re-projected (the dataset remains unchanged, though). For this,  
>>> it is required that your layer has a projection object with the  
>>> native projection of that layer. This will cause the layer to be  
>>> reprojected along with the map. Is this what you are trying to do?
>>>
>>> You *may* have to save your mapfile, or your session, in order  
>>> for it to take effect, depending on your setup.
>>>
>>> regards,
>>>
>>> Jacob
>>>
>>>
>>> From: UMN MapServer Users List [mailto:MAPSERVER- 
>>> USERS at LISTS.UMN.EDU] On Behalf Of Stefan Schwarzer
>>> Sent: 24 August 2006 13:45
>>> To: MAPSERVER-USERS at LISTS.UMN.EDU
>>> Subject: Re: [UMN_MAPSERVER-USERS] Mapscript Re-Projection on-the- 
>>> fly
>>>
>>> Hey,
>>>
>>> I can't imagine that such a question stays unanswered in the  
>>> mapserver community...
>>>
>>> I meanwhile added a:
>>>
>>> $map -> setProjection("init=epsg:26711");
>>>
>>> to my code, but nothing happens - meaning: no error message but  
>>> no reprojection either.
>>>
>>> Can anyone help me out?
>>>
>>> Thanks in advance.
>>>
>>> Stefan
>>>
>>>
>>> On Aug 22, 2006, at 10:47 AM, Stefan Schwarzer wrote:
>>>
>>>> Gush,
>>>>
>>>> I couldn't find any precise information about how to re-project  
>>>> layers on-the-fly via PHP Mapscript. Here and there (via  
>>>> MailingList and Google) bits and pieces, but altogether it  
>>>> didn't help me a lot. Though I would have said that this is a  
>>>> basic question. But perhaps too basic, so everbody finds out by  
>>>> himself?
>>>>
>>>> So, can anyone let me know - giving a coding example - how to re- 
>>>> project a mapfile on-the-fly from for example Lat/Long (global  
>>>> view) to Lambert or Robin?
>>>>
>>>> Thanks a lot for your help!
>>>>
>>>>
>>>
>>
>

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