[Proj] ITRF96/UTM 36N conversion
Jose Gonçalves
jagoncal at gmail.com
Sun Aug 9 07:18:07 EST 2009
Mr. Gerald Evenden can clear your doubts about GEOD, since he is the author
of the program. I have used it only occasionally.
Anyway some comments on your experiments: If you are comparing distances at
millimetre level be aware that when you round your geographic coordinates
with 3 decimal places in seconds you are introducing an error of up to 1.5
cm, so your distance can be affected by a few centimetres. You can increase
the decimal places of the proj output (-W5, for 5 decimal places in seconds
or use decimal degrees).
If your distances are that small, i.e., just a few meters, then you can
calculate the distance in UTM just as the Euclidean distance
(sqrt((x2-x1)^2+(y2-y1)^2)). The deformation in UTM projection (within one
zone) is most of the times smaller than 40 cm per km, and you can calculate
it and apply it if needed.
Regards
Jose Gonçalves
2009/8/8 fernandohoze <muranyum at yahoo.com>
>
>
> José Alberto Gonçalves wrote:
> >
> > In order to convert UTM-36N to long-lat with output in decimal degrees
> you
> > can use the following PROJ command line:
> > proj -I -f "%.9f" +ellps=WGS84 +proj=utm +zone=36
>
> Thank you all for your replies. I tried the command José wrote (with -r
> flag
> - thanks Gerald) and it worked well. The command also works without
> reformatting the input.
>
> About calculating distance between two points... José, I examined the
> program you recommended but and I have some results but I need to make sure
> that they are correct. Here is what I did:
>
> First of all, here are the input points:
>
> 4415488.923061 481668.789218
> 4415490.272973 481668.977703
>
> I found latitude and longtitude using the following command:
>
> proj -r -I -f "%.9f" +ellps=WGS84 +proj=utm +zone=36
>
> Results:
>
> 32.785593500 39.889265833
> 32.785595667 39.889278000
>
> So, when I wrote these into Google Maps (in reverse order,) it correctly
> showed the points:
>
> 39.889265833 32.785593500
> 39.889278000 32.785595667
>
> Then, I executed the following geod command:
>
> geod +ellps=WGS84
>
> As input I wrote the above numbers. As output I received the latitude and
> longtitude in degree/minute/second format:
>
> 39d53'21.357"N 32d47'8.137"E 180d
> 39d53'21.401"N 32d47'8.144"E 180d
>
> Then, I executed this command for distance calculation:
>
> geod +ellps=WGS84 -I +units=km
>
> And entered the above coordinates as input:
>
> 39d53'21.357"N 32d47'8.137"E 39d53'21.401"N 32d47'8.144"E
>
> The result was:
>
> 6d59'12.829" -173d0'47.167" 0.001
>
> 0.001 at the end of the result tells that the distance is around 0.001 km
> that is 1 meters. So, I tried the command with +units=m and the result was
>
> 6d59'12.829" -173d0'47.167" 1.368
>
> That is 1.368 meters, which seems to be correct. I did the same calculation
> using http://www.movable-type.co.uk/scripts/latlong.html this web page
> and
> the result was 0.001369 km. So, I guess I used the correct commands. The
> inputs I used for the web page were like that:
>
> Lat 1: 39 53 21.357N
> Long 1: 32 47 8.137E
> Lat 2: 39 53 21.401N
> Long 2: 32 47 8.144E
>
> There is one problem here that I don't get. When I use cm or dm for +units
> option, I still get 1.368 insted of 136.8 for cm and 13.86 for dm.
> Actually,
> if I don't use any +units option, I still get 1.368 as the result. Is there
> something wrong with the command I use or am I missing something?
>
> I also tried everything above with the following inputs:
>
> 4415475.022910 481656.729116 918.850000
> 4415473.636002 481656.540539 918.850000
>
> And in the end I got 1.195 as the results, which is reasonable. The web
> site
> gave 0.001194 km.
>
> I tried to write everything I did step by step. Could you please tell me if
> above calculations are correct or not. Also I would appreciate if you tell
> me a command that would do all the computation above.
> --
> View this message in context:
> http://n2.nabble.com/ITRF96-UTM-36N-conversion-tp3404575p3409993.html
> Sent from the PROJ.4 mailing list archive at Nabble.com.
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