| Re: UTM map [message #40265 is a reply to message #6894] |
Fri, 30 July 2004 01:16   |
sso
Messages: 13
Registered: February 2002
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Junior Member |
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Ben Tupper <btupper@bigelow.org> wrote in message news:<2mps37Fq1sctU1@uni-berlin.de>...
> Sverre Solberg wrote:
>> Is there any possibility to draw a rectangular grid (with typically
>> 30x40 grid cells in XxY direction) on a standard UTM map in idl? What
>> I'm looking for is a standard plot presenting numerical model results
>> with the grid cells coloured according to the values. The map itself
>> is easy enough to make but when overplotting squares with fixed
>> distance (in meters) the grid lines get "zig-zaged" when converted to
>> lat/lon. Do I e.g. have to split the grid lines into an extremely dens
>> row of UTM coordinates and then convert to lat/lon? A bit awkward. As
>> far as I know, idl hasn't any functionality for UTM map coordinates,
>> or am I wrong?
>>
>
> Hi,
>
> Starting with IDL 5.6, the handy MAP_PROJ_**** routines have made life a lot
> easier to deal with map coordinate conversions. These should help you with the
> forward and backward coordinate transformations. I'm not sure if this will help
> answer your question... which is ... well, what is your question again?
>
> Someday I'm gonna write a guide to mapping in IDL and throw in a nice GUI
> interface to the MAP_PROJ_INIT function. Just as soon as I figure it all out.
> Considering that I have frequently fussed with mapping in IDL for a long time
> and still have to start from scratch each time, it could be a while.
>
> Ben
Thanks. We are still using the 5.5 version so upgrading will be good
then. The problem which is now partly solved, was the following: I
have a rectangular UTM grid with a grid spacing of 5km in x- and
y-direction. I use your utm_to_ll routine to convert (each grid cell)
to geo. coordinates. However, when plotting this on top of the map
produced by the map_set,/trans routine the grid looks like it's
handdrawn with "bumpy" grid lines. I thought this was due to the
UTM->geo conversion but discovered that it was only seen on the screen
or if printed to a bitmap file. When making e.g. a cgm (or PS) file
the lines are perfectly straight. So this helps a lot, but still I'm
confused why the lines are not staight on the screen, and since this
is part of widget system with a clickable map, it's still a slight
problem.
Sverre
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