[GRASS-user] Display of lat long with WTM83, NAD83 based map

[Hamish]

John wrote:
> I have an aerial photo referenced with WTM83, NAD83. It is loaded into 
> GRASS and I can successfully overlay a grid such as this:
> 
> 	d.grid size=50 origin=0,0  color=0:255:255 bordercolor=0:0:0
> 
> However, this displays the coordinates with the above reference (meter 
> based).  I would like to display latitude and longitude in degrees.

The -g or -w flags are for this.

> Do I need to modify the image file to do this?

No.

> Are there options in GRASS to display lat long without changing the 
> image file?

The -g or -w flags are for this.
 
> Because d.grid -g option wants a lat long database

No it doesn't. It is for drawing lat long lines in a projected location.
Actually in a lat/lon location you specifically don't want to use the -g flag.

> and I can't seem to generate the -w option from gis.m, I am not sure where
> to go with this.

I'm not sure about using -w from gis.m, a GUI programmer would have to comment,
but the minimal difference between the WGS84 and NAD83 should mean there isn't
too much difference between the two methods anyway. (but do overlay the two to
check)

Note that 'd.grid -g size=50' will draw a 50 degree planetary-scale grid, you
probably want something like size=0:00:30 for a 30" grid.

It all should work. I suspect you are 99% of the way there and only have to
adjust the grid size.


good luck,
Hamish



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