| wrong results... [message #43811] |
Mon, 02 May 2005 06:49  |
elias
Messages: 13
Registered: April 2005
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Junior Member |
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Hi,
The following problem probably has something to do with definitions of
floating, integer etc, but I don't really know to solve it (although i
am sure the solution will be simple in the end...).
I have a data file that, amongst others, contains some longitude
columns. The longitude data is defined from -180 to 180 deg in this
data file. For some consistency with some other analysis I did before,
I want to convert it to 0-->360 deg.
So simply, I ask when it reads a longitude <0 to do: lon=360+lon
However, I am getting in the new data file created, values of longitude
more than 600 sometimes.... I am not sure why this happens
Below I post this simple code.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
PRO restruct, fil, output
;reads data file of moon l-shell
;crossings and restructures its data
;so that:
;Cassini and Moon longitude>0
;(Cassini-Moon) longitude>0
filetemplate=ASCII_Template(fil)
data=Read_ASCII(fil,Template=filetemplate)
crossings=n_elements(data.field1)
openw, lunit, /get_lun, output
for i=0L,crossings-1 do begin
if data.field3[i] lt 0 then begin
data.field3[i]=360+data.field3[i]
endif
if data.field6[i] lt 0 then begin
data.field6[i]=360+data.field6[i]
endif
dlon=data.field6[i]-data.field3[i]
if dlon lt 0 then begin
data.field3[i]=360+data.field3[i]
endif
thisformat='(f14, 7f14)'
printf, lunit, data.field1[i], data.field2[i],$
data.field3[i], data.field4[i],$
data.field5[i], data.field6[i],$
data.field7[i], dlon, format=thisformat
endfor
free_lun, lunit
end
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| Re: wrong results... [message #43924 is a reply to message #43811] |
Tue, 03 May 2005 15:56  |
Ken Mankoff
Messages: 158
Registered: February 2000
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Senior Member |
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On Tue, 3 May 2005, yp wrote:
> Kenneth Bowman wrote:
>>
>> lon = (lon + 360.0) MOD 360.0
>>
>
> Thats brilliant!
>
>> By the way, the reverse transformation is
>>
>> lon = lon - (LONG(lon)/180)*360.0
>>
>
> This is great too; but how to parse the last element? Using the
> above transformation, 180.0 becomes -180.0 at both ends. This does
> transform the coordinate exactlty for all elements except +180.0.
> Of course, zonally 180 = -180 from a geographic perspective.
The IDL astronomy library has a CIRRANGE procedure (circle range)
that forces things to 0->360. It is pretty easy to modify it to a
RANGECIR procedure that does the -180 to 180 range. Works for
radians too via a keyword. Check it out, it might be a good starting
place.
-k.
--
http://spacebit.dyndns.org/
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