[GRASSLIST:10326] Re: robinson (winkel) projection

[Ian MacMillan]

William, I have not seen this with my Robinson locations.  Are you sure 
about this?  Could it be that your original dataset was using a sphere 
but you imported it into a wgs84 location.  I had this trouble 
originally with Smith and Sandwell data.  Seems like a major bug if 
your observation is true.  Has anyone else ever seen this with Robinson 
projections?

-Ian


On Feb 15, 2006, at 11:00 AM, William Kyngesburye wrote:

> One important thing I found - use a sphere, not an ellipsoid.  If you 
> use an ellipsoid, there will be an approx. 20000m N-S shift at around 
> 45 deg N and S (for the Robinson, at least), which is quite noticable 
> at any scale.  I agonized over this for a while, using WGS84 ellipsoid 
> out of habit, and even thought it was a bug, until I figured out the 
> cause.  -> use a sphere for global projections.
>
>
> On Feb 15, 2006, at 12:29 PM, Ian MacMillan wrote:
>
>> Otto, I have made some robinson locations for my work, and the 
>> process is pretty straight forward.  After selecting 'create new 
>> location' when first opening grass, select that you would like to use 
>> 'Other Projection' when asked for your coord. system.  When asked to 
>> specify your projection name, just use 'robin'.  Select your datum as 
>> usual.  You will then have to input your central parallel, central 
>> meridian, and preferred units.  For most robinson projections that 
>> you see in atlases, the central parallel is the equator (0), and the 
>> central meridian is the Greenwich meridian (also 0).  I usually use 
>> meters as my preferred units.
>>
>> Degrees would be really nice as a standard unit for these kinds of 
>> projections, but since their absolute length varies depending on your 
>> location on the earth, they can't be used in grass.  My workaround to 
>> this has been to make a vector grid in a latlong location that is 
>> spaced about ten or fifteen degrees apart for the entire earth.  I 
>> then project (with v.proj) that vector file into my robinson location 
>> as a first step so that I can see where I am in the world.
>>
>> Once you are done with all of that, use r.proj and v.proj at your 
>> leisure in your new location.
>>
>> Hope this helps,
>> Ian
>>
>> On Feb 15, 2006, at 4:25 AM, Otto Dassau wrote:
>>
>>> Hi,
>>>
>>> I would like to convert a lat/lon map into a robinson (winkel) 
>>> projection.
>>>
>>> does anybody has experience with the creation of a robinson (winkel)
>>> projektion in GRASS? It seems to be supported (robin, winkel,...) 
>>> but I
>>> haven't found out, how to create a robin location in GRASS and which
>>> parameters a normaly used.
>>>
>>> thanks
>>>   Otto
>
> -----
> William Kyngesburye <kyngchaos at kyngchaos.com>
> http://www.kyngchaos.com/
>
> [Trillian]  What are you supposed to do WITH a maniacally depressed 
> robot?
>
> [Marvin]  You think you have problems?  What are you supposed to do if 
> you ARE a maniacally depressed robot?  No, don't try and answer, I'm 
> 50,000 times more intelligent than you and even I don't know the 
> answer...
>
> - HitchHiker's Guide to the Galaxy
>
>
 >
 >
What happens if a big asteroid hits Earth? Judging from realistic 
simulations involving a sledge hammer and a common laboratory frog, we 
can assume it will be pretty bad.
  - Dave Barry


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