[GRASSLIST:5938] Re: Multiple coordinate systems

[Phillip J. Allen]

John,

With being a geochemist I often have to work with samples taken along 
lines (north & non-north) and plot them on a UTM map.  I personally just 
load all my data into a database (I like PostgreSQL, but anything is 
good) which has grid and utm coordinate columns.  Then I have a few 
functions (in postgresql and MS Access) that based upon the usergrid 
base-point and degrees of rotation from north, transform all my 
coordinates to UTM or geographic.  For me it's always more convient to 
let my database handle all the coordinate transformations because often 
there is a mixture of samples collected with UTM, usergrid, or 
geographic coordinates or even drill/trench samples (that have a collar 
point, orientation, and from-to distances).  Now with all the samples 
having the same type of coordinates everything can be pulled into the 
map as one big layer if necessary.  And regenerations are faster.

Your e-mail indicates that you are dealing with geophysics and I will 
guess that you are trying to overlay some of those lovely non-north 
grids based upon lines that the project geo layed out for you.  I know 
they are necessary but they drive me crazy too.  But again I have been 
hearing that PostGIST with possibly or can now handle grid data.  In the 
future I think rdms based data will be the proper route even for 
cross-sections such as IP lines.  For one of my clients I have 
PostgreSQL views that transform the sample coordinates (UTM E/N/Elev) to 
user-defined cross-sections coordinates to plot them up in ArcView or 
MapInfo.     

good luck,

Phillip J. Allen
Consulting Geochemist/Geologist
Lima Peru
e-mail: paallen at attglobal.net


John Harrop wrote:

> Hi,
>
> I've not been able to come up with a comfortable way of handling 
> projects with multiple coordinate systems in grass.  Perhaps I'm 
> missing something...
>
> Our typical project uses at least two coordinate systems.  One is a 
> local coordinate system oriented by data collection methods and used 
> for processing of such data.  The second is usually a UTM projection 
> and most final maps are produced in this projection.  The relationship 
> between the two is a simple shift and rotate operation since the areas 
> we are working with are quite small.
>
> I can see how to transform one mapset while importing into another 
> mapset, but after that is done you obviously have a potential map 
> version conflict when one but not the other is updated with new data.
>
> Is there a way to overlay different projections and/or non-earth 
> coordinate systems in grass on-the-fly?  (Similar to how MapInfo and 
> other systems handle it.)
>
> Any comments folks?
>
> Thanks,
>
> John Harrop
>
>