[GRASSLIST:2374] Re: v.proj help

[Christian G. Tveen]

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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