| "TRUE" map projections [message #3431] |
Tue, 24 January 1995 13:34  |
afl
Messages: 51
Registered: December 1994
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Member |
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How can one obtain (for example) a "true" Mercator map
projection in IDL? Sounds rather academic, doesn't it?
But in a given window if one issues
IDL> map_set, /merc, /cont, /grid, /usa, limit=[15,-130,50,-60]
vs.
IDL> map_set, /merc, /cont, /grid, /usa, limit=[15,-180,50,-30]
I guaranteee you the "shape" of the geographical boundaries
will be different. There must be a single, proper aspect ratio for
a map to be called a "true" Mercator projection. Is IDL capable
of producing "true" map projections, or is one able to arbitarily
re-shape the projection into any form he wishes such that the
specification of the projection is all but pointless? Does one
simply say "hmmmm, looks good to me" and move onto the next task?
--
Andrew F. Loughe email: afl@cdc.noaa.gov
University of Colorado, CIRES voice: (303) 492-0707
Campus Box 449 fax: (303) 497-7013
Boulder, CO 80309-0449 USA
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| Re: "TRUE" map projections [message #3473 is a reply to message #3431] |
Tue, 31 January 1995 05:54  |
Serdar Manizade
Messages: 15
Registered: December 1994
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Junior Member |
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afl@bjerknes.NoSubdomain.NoDomain (Andy Loughe) wrote:
>
> In article <3gjeud$t4g@post.gsfc.nasa.gov>, Serdar Manizade <manizade@osb1.wff.nasa.gov> writes:
> |> afl@bjerknes.NoSubdomain.NoDomain (Andy Loughe) wrote:
> |> > ...
> |> > than I--> "Use the /ISO keyword in your map_set call."
> |> > Is the ISO keyword a documented feature in IDL?
> |> > "No comment."
> |> ...
> |> I tried it. I did not find iso mentioned in the on-line documentation
> |> for map_set. (I am running: IDL. Version 3.6 (sunos sparc).)
> |> ...
> I am running IDL Version 3.6.1a (sunos sparc), and the /ISO
> keyword works with map_set. I cannot vouch for earlier versions.
Thanks to Andy Loughe and Marion Legg. I updated to 3.6.1a and
now have the /iso keyword to map_set. Now if only I had some
documentation to understand what it does...
Serdar
EG&G/ NASA Wallops Flight Facility, Virginia, USA
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| Re: "TRUE" map projections [message #3479 is a reply to message #3431] |
Mon, 30 January 1995 14:54 |
afl
Messages: 51
Registered: December 1994
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Member |
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In article <3gjeud$t4g@post.gsfc.nasa.gov>, Serdar Manizade <manizade@osb1.wff.nasa.gov> writes:
|> afl@bjerknes.NoSubdomain.NoDomain (Andy Loughe) wrote:
|> > ...
|> > than I--> "Use the /ISO keyword in your map_set call."
|> >
|> > Is the ISO keyword a documented feature in IDL?
|> >
|> > "No comment."
|>
|> Perhaps you are speaking tongue-in-cheek, but I am gullible, so
|> I tried it. I did not find iso mentioned in the on-line documentation
|> for map_set. (I am running: IDL. Version 3.6 (sunos sparc).)
|>
|> IDL> map_set
|> % Compiled module: MAP_SET.
|> IDL> map_set,/iso
|> % Keyword ISO not allowed in call to: MAP_SET
|> % Execution halted at $MAIN$ .
|>
|>
I am running IDL Version 3.6.1a (sunos sparc), and the /ISO
keyword works with map_set. I cannot vouch for earlier versions.
--
Andrew F. Loughe email: afl@cdc.noaa.gov
University of Colorado, CIRES voice: (303) 492-0707
Campus Box 449 fax: (303) 497-7013
Boulder, CO 80309-0449 USA
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| Re: "TRUE" map projections [message #3483 is a reply to message #3431] |
Mon, 30 January 1995 11:33 |
Serdar Manizade
Messages: 15
Registered: December 1994
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Junior Member |
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afl@bjerknes.NoSubdomain.NoDomain (Andy Loughe) wrote:
> ...
> than I--> "Use the /ISO keyword in your map_set call."
>
> Is the ISO keyword a documented feature in IDL?
>
> "No comment."
Perhaps you are speaking tongue-in-cheek, but I am gullible, so
I tried it. I did not find iso mentioned in the on-line documentation
for map_set. (I am running: IDL. Version 3.6 (sunos sparc).)
IDL> map_set
% Compiled module: MAP_SET.
IDL> map_set,/iso
% Keyword ISO not allowed in call to: MAP_SET
% Execution halted at $MAIN$ .
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| Re: "TRUE" map projections [message #3495 is a reply to message #3431] |
Fri, 27 January 1995 09:32 |
zawodny
Messages: 121
Registered: August 1992
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Senior Member |
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In article <3gb5au$o3i@post.gsfc.nasa.gov> Serdar Manizade <manizade@osb1.wff.nasa.gov> writes:
> I repost my note since subject was missing. Apologies.
> Serdar Manizade <manizade@osb1.wff.nasa.gov> wrote:
>>
>> zawodny@arbd0.larc.nasa.gov (Joseph M Zawodny) wrote:
>>> possible I use "circular" map projections and the SET_ISOXY routine. But,
>>
>> Where is the SET_ISOXY routine?
>>
>> When I produce a map, I have to pull out my ruler and measure the
>> latitude and longitude scales to see if I got the scaling right. I
>> make adjustments whenever I change my output map aspect ratio or the
>> coordinates of the map. Especially important at high latitudes.
>
This is my version of the routine set_isoxy. It was part of a system of
routines writen by the original author. I hacked it a bit to work by
itself without the need for the other routines. It works for what I use it
for but it may nolonger function as the original author intended. I make
no claims of functionality for either myself or the original author. Look
it over, try it out and hack it further to suit your needs.
PRO SET_ISOXY, XMN0, XMX0, YMN0, YMX0
;+
;----------------------------------------------------------- -------
; Name: SET_ISOXY.PRO
; Purpose: Set XY isotropically (equal x and y scale).
; Category: Graphics.
; Calling sequence: SET_ISOXY, XMN, XMX, YMN, YMX
; Inputs:
; XMN = minimum data x. in.
; XMX = maximum data x. in.
; YMN = minimum data y. in.
; YMX = maximum data y. in.
; Optional input parameters:
; Outputs:
; Optional output parameters:
; Common blocks: ISOXY_COMMON = what parts of data window to lock in place.
; Side effects:
; Restrictions:
; Routines used:
; Procedure:
; Modification history:
; 3 Sep, 1986. R. Sterner. Johns Hopkins U APL
; Jun 14, 1990. J.M. Zawodny NASA LaRC modified for standalone to V-2.0
;----------------------------------------------------------- -------
;-
COMMON ISOXY_COMMON, X_LOCK, Y_LOCK
IF N_PARAMS(0) EQ 0 THEN BEGIN
PRINT,'SET_ISOXY, XMN, XMX, YMN, YMX
PRINT,' XMN, XMX = desired min and max X.
PRINT,' YMN, YMX = desired min and max Y.
PRINT,' Either XMN, XMX or YMN,YMX will be adjusted to force equal scaling in
PRINT,' X and Y in the set screen window. At least the specified range will
PRINT,' be covered in both X and Y, but a greater range will be covered in one.
RETURN
ENDIF
IF N_ELEMENTS(X_LOCK) EQ 0 THEN X_LOCK = 'XMD' ; defaults.
IF N_ELEMENTS(Y_LOCK) EQ 0 THEN Y_LOCK = 'YMD'
XMN = XMN0 ; copy so changing values
XMX = XMX0 ; won't change them in caller.
YMN = YMN0
YMX = YMX0
; if !p.position not set default to largest area possible
m=where(!p.position ne 0.,count)
if(count eq 0) then !p.position=[0.,0.,1.,1.]
IDX = (!p.position(2)-!p.position(0))*!d.x_vsize ; plot position
IDY = (!p.position(3)-!p.position(1))*!d.y_vsize ; side lengths
DX = FLOAT(XMX - XMN) ; data window side lengths.
DY = FLOAT(YMX - YMN)
YMD = .5*(YMN + YMX) ; data window midpoint.
XMD = .5*(XMN + XMX)
IF (DX/DY) GE (IDX/IDY) THEN BEGIN ; adjust Y range.
DY2 = .5*DX*IDY/IDX ; half new Y range.
DX2 = .5*DX ; half old X range.
ENDIF ELSE BEGIN ; adjust X range.
DX2 = .5*DY*IDX/IDY ; half new X range.
DY2 = .5*DY ; half old Y range.
ENDELSE
;--------- lock window -----------------
CASE X_LOCK OF ; lock x.
'XMN': XMX = XMN + DX2 + DX2 ; lock x min.
'XMD': BEGIN ; lock x mid.
XMN = XMD - DX2
XMX = XMD + DX2
END
'XMX': XMN = XMX - DX2 - DX2 ; lock x max.
ENDCASE
CASE Y_LOCK OF ; lock y.
'YMN': YMX = YMN + DY2 + DY2 ; lock y min.
'YMD': BEGIN ; lock y mid.
YMN = YMD - DY2
YMX = YMD + DY2
END
'YMX': YMN = YMX - DY2 - DY2 ; lock y max.
ENDCASE
!x.range=[XMN, XMX]
!y.range=[YMN, YMX]
RETURN
END
--
Joseph M. Zawodny (KO4LW) NASA Langley Research Center
Internet: j.m.zawodny@larc.nasa.gov MS-475, Hampton VA, 23681-0001
TCP/IP: ko4lw@ko4lw.ampr.org Packet: ko4lw@n4hog.va.usa.na
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| Re:"TRUE" map projections [message #3496 is a reply to message #3431] |
Fri, 27 January 1995 08:00 |
Serdar Manizade
Messages: 15
Registered: December 1994
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Junior Member |
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I repost my note since subject was missing. Apologies.
Serdar Manizade <manizade@osb1.wff.nasa.gov> wrote:
>
> zawodny@arbd0.larc.nasa.gov (Joseph M Zawodny) wrote:
>> possible I use "circular" map projections and the SET_ISOXY routine. But,
>
> Where is the SET_ISOXY routine?
>
> When I produce a map, I have to pull out my ruler and measure the
> latitude and longitude scales to see if I got the scaling right. I
> make adjustments whenever I change my output map aspect ratio or the
> coordinates of the map. Especially important at high latitudes.
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