Hi! Sorry for not answering this for a day or so. First of all thanks to Ed and Frank for helping me out on this one!
What you explain is what I figured happened. But I still do not quite understand why proj cannot transform my coordinates to the new system with the latitude shifted. I have read one similar e-mail on this list from 2005(although I cannot find it now) which asked the same question. Espen On 17/01/2008, Ed McNierney <[EMAIL PROTECTED]> wrote: > Espen - > > Yes, that should be what you expect. If you change the latitude of true > scale, then you're changing the relationship between the size of a > degree of longitude at a given latitude. Normally the line of 60 > degrees North latitude is "stretched" horizontally to be larger than it > should be. It is displayed so that it appears that one degree of > longitude (at that latitude) is the same size as one degree of longitude > at the Equator (instead of being only half as long). That makes it > appear to be the same size as a degree of latitude and therefore you can > easily interpolate coordinates because they are the same size. > > When you change the latitude of true scale to 60 degrees North, you are > making every degree of longitude equal 0.5 degrees of latitude, and you > can no longer treat them as simple X/Y coordinates to read latitude and > longitude. You need to keep in mind that you are really using a > different projection, so your coordinate system is going to be > different. > > - Ed > > -----Original Message----- > From: UMN MapServer Users List [mailto:[EMAIL PROTECTED] On > Behalf Of Espen Isaksen > Sent: Wednesday, January 16, 2008 5:41 PM > To: [email protected] > Subject: Re: [UMN_MAPSERVER-USERS] Plate Carre with latitude shift > > To further discuss this topic. I created a map of Europe in a regular > EPSG:32662(proj=eqc) and one map of Europe with a latitude shift to 60 > degrees north: > > Map of Europe in 32662: > http://bildr.no/view/143324 > > Map of Europe with latitude shift: > http://bildr.no/view/143325 > > The latter is close to what I want. However, if I move my zoom in to > some part of the nordic countries, the decimal degree coordinates will > no longer correspond with my coordinates in my 32662 projection with > the latitude shift. Why is this? > > Espen > > > On 16/01/2008, Espen Isaksen <[EMAIL PROTECTED]> wrote: > > > EPSG:4326 is a geographic coordinate system, and the coordinates > are in > > > decimal degrees. +proj=eqc is a projected coordinate system and the > > > coordinates are meters. The location (-180,90) would be roughly > > > (-20000000,100000). > > > > > > Essentially eqc (ie. equidistant cylindrical or Plate Carree) is > just > > > a rescaling of EPSG:4326 from degrees to meters. > > > > > > > Ok I understand this. > > > > > I'm afraid I just don't get what you hope to accomplish with > +lat_ts=60. > > > Are you hoping to get one projected meter being one meter on the > ground > > > at 60N as opposed to it being one meter at the equator as is the > default? > > > I'm not aware of proj=eqc supporting any such option. > > > > Yes I am trying to change the projection such that it gets less > > distorted in areas near the north pole. I tried to set the mapfile > > like this: > > > > EXTENT 593674.73 6669772.29 594581.49 6670417.57 > > PROJECTION > > "+proj=eqc +lat_ts=60 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 > > +datum=WGS84 +no_defs +units=m" > > END > > > > which seems to create an quite ok map. Much better than setting > > +lat_ts=0. Although I do not understand why Mapserver creates a map > > over a different area than what my original decimal degree areas > > indicates(I used proj to convert them)? > > > > By the way my original decimal degree coordinates are: > > 10.6661 59.9155 10.6824 59.9213 > > > > Perhaps what I am doing is just nonsense... > > > > Espen > > >
