[GRASSLIST:2375] Re: v.proj help

[Christian G. Tveen]

Forgot to mention that fixing the WIND to use meters instead of lat-lng, 
the d.vect works fine.

Regards.


Christian G. Tveen wrote:

> Thanks a lot!!!
> I had't really realized that units had to be meters (I'm very much 
> used to only use lat/lng even in projected maps.)
>
> I have two further questions: From where did you obtain the precise 
> values for the boundaries ? (I saw my rounded values written by v.proj)
>
> A more general question is how to obtain the initial WIND/DEFAULT_WIND 
> file. When starting out, I only have the LL boundaries. Do I manually 
> calculate the Mercator boundaries for those files, or is there a 
> clever way ? (g.region initially requires a DEFAULT_WIND file, so 
> somehow I need a boot-strap)
>
> Best regards
> Christian
>
> Glynn Clements wrote:
>
>> Christian G. Tveen wrote:
>>
>>  
>>
>>> Then I've tried to project the data to mercator projection, into a 
>>> new handmade location. Here I cant display the projected data ! The 
>>> projection was done by inserting the following PROJ_INFO into the 
>>> new location/PERMANENT:
>>>
>>> name: Mercator
>>> proj: merc
>>> ellps: clark66
>>> lat_0: 57.0
>>> lon_0:11.0
>>> zone: -1
>>>   
>>
>>
>> lat_0 isn't a valid parameter for that projection.
>>
>>  
>>
>>> To get the WIND and DEFAULT_WIND files, I did a g.region on the 
>>> imported file and changed the projection to 99
>>> The WIND file looks like:
>>>
>>> proj: 99
>>> zone:0
>>> north: 57:54:28N
>>> south: 54:24:11N
>>> east:    15:33:24E
>>> west: 7:38:57E
>>> cols: 99
>>> rows: 44
>>> e-w resol: 0:04:47.54
>>> n-s resol: 0:04:46.75
>>>   
>>
>>
>> This isn't valid. The region boundaries and resolution have to be
>> specified in the map's coordinate system (i.e. feet/metres, not
>> degrees).
>>
>>  
>>
>>> I think the
>>> THen v.proj -s input=ponet location=global mapset=dk
>>>
>>> The output is somewhat big numbers:
>>> north: 7911408
>>> south: 7211788
>>> east 502391
>>> west 364972
>>>   
>>
>>
>> If I project your lat/lon region into the location:
>>
>>     name: Mercator
>>     proj: merc
>>     ellps: clark66
>>     lat_ts: 0.0000000000
>>     lon_0: 11.0000000000
>>     k_0: 1.0000000000
>>
>> I end up with:
>>
>>     north:      7904761.9047619
>>     south:      7206349.20634921
>>     west:       -369444.44444444
>>     east:       504166.66666667
>>
>> Which isn't that far off, except for the Western boundary. Maybe
>> something doesn't like the negative coordinate; most map projections
>> choose their parameters so that coordinates are always positive (e.g.
>> by adding a false Easting or Northing).
>>
>>  
>>
>

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