[GRASSLIST:4691] Re: robinson projection

[William K]

And the Van der Grinten.  The wrap-around isn't even useful on this 
projection - it's messed up.  The corners bend up too quickly.

My solution to this wrap-around - divide the source raster into east 
and west halves at 0 long.  Project each separately into half of the 
desired projection, then patch them together.  If you are worried about 
interpolation issues along the join line, another way is to set up a 
mask in the source location in east and west halves.  Project the full 
raster as usual.  Project the mask halves into half of the desired 
projection with a nearest neighbor, patch those together and use it to 
mask the raster.

I have my GLOBE data set up this way.  A little extra projecting work, 
but it does the job.


On Oct 28, 2004, at 9:35 PM, Ian MacMillan wrote:

> I noticed that I had the same problem if I used a Winkel Triple 
> projection instead of a Robinson projection.  It seems like a function 
> that might be used a lot is one that lays down a latlong grid in any 
> projection, but maybe that is just me.  In any case, as a workaround, 
> I made a grid in 5.3 with v.mkgrid (unfortunately not available in 
> 5.7) in my latlong location, projected it into the robinson location 
> with v.proj, and converted it to a 5.7 vector with v.convert.  Worked 
> like a charm.
>
> -Ian
>
>
> On Oct 28, 2004, at 6:12 PM, Ian MacMillan wrote:
>
>> Hi all again, I have a weird problem.  I am trying to make a world 
>> map using the robinson projection.  I have projected in a raster map 
>> of the world into this location, and instead of obtaining the nice 
>> oval-ish shape we are used to, the new raster is a rectangle with 
>> areas at the edges duplicated.  The edges are distorted as they 
>> should be, but there is no way to determine where the edges of the 
>> original map lay.  I figured this is ok if I could project in a 
>> vector box of the world (from a latlong location), and just use that 
>> as a mask.  Trouble is that when I project in a vector area with 
>> bounding coordinates of n=72 s=-72 e=180 w=-180 in latlong space, it 
>> comes into the Robinson location as a box, not an oval-ish shape.  
>> This doesn't make any sense to me.  Is this a problem with proj.4?  
>> Or is it impossible to delineate lines of longitude in the Robinson 
>> projection (measurement units are meters)?
>>
>> Thanks for any input y'all might have,
>> Ian
>>
>
>
-----
William Kyngesburye <kyngchaos at charter.net>
http://webpages.charter.net/kyngchaos/

"Mon Dieu! but they are all alike.  Cheating, murdering, lying, 
fighting, and all for things that the beasts of the jungle would not 
deign to possess - money to purchase the effeminate pleasures of 
weaklings.  And yet withal bound down by silly customs that make them 
slaves to their unhappy lot while firm in the belief that they be the 
lords of creation enjoying the only real pleasures of existence....

- the wisdom of Tarzan