[GRASS-user] UTM values.

[Micha Silver]

ambrish dhaka wrote:

> I have the following Long lat and UTM values from the converters.
Can you explain what you mean by "converters"?
>
> 24.5N -2711052
> 41E    -702655
>
> 47N -5209532
> 84E  -271930
As you probably know, the two lon values above are in widely separated 
UTM zones. 41E is in zone UTM37N while 84E is in zone UTM 45N. These two 
UTM zones are actually two *different* projections - with different 
origins.
Just to give another example:
Jerusalem is at 35.21E x 31.78N. It is located in UTM zone 36N, and the 
UTM coords work out to 709266 x 3518175
Damascus is slightly east of Jerusalem at 36.32E x 33.5N. But this city 
is in UTM zone 37N so the coordinates are 251031 x 3709934.
Similar to your case, a location further east has a *smaller* X 
coordinate in UTM since it has shifted to the next zone.
>
> The problem is while defining the region. you can see the UTM value of 
> 84E is smaller than the value of 41E, which is the value of west 
> bounds. The problem is that why the converter is giving the lesser 
> values for higher longitude which the QGIS refuses to accept and also 
> if I put the random value of 2000000 for the east bounds, i.e., 
> against the 84E bounds the desired region is shown by the red box but 
> the longitude value is more than 100E which is very large area.
> So this puzzle needs to be resolved. Kindly provide me the correct UTM 
> values for above bounds and which converter to use. Also, the datum 
> changes from 37 to 45 N so I decide to define an average datum of 41N 
> for my projection; is it ok!
UTM is not suitable for geographic regions with a very large E-W extent.

Regards,
Micha
>
> Thanks!
> Ambrish Dhaka
>