Different lat-lon grid size for geographic grids

[alf]

When setting locations at high latitudes, the meridians / parallels spacing ratio tend to be small. Find attached an example of a lcc grid with projection at high lats (lcc_geogrid.png).

In order to have a better output we could introduce parameters for optional separate ew and ns (geo)grid sizing.

Also it will be important to set a minimum/maximum for grid drawing, so we can avoid cluttering the maps as soon as meridians become too dense (e.g. in polar areas).

Alessandro Frigeri

[alf]

Geogrid for lcc projection at high latitudes: effect of a single 'size' parameter for geogrid

[hamish]

work around: run d.grid at the desired longitude spacing, and then again with the grid size set to the latitudes you want grid lines at.

so for your example:

d.grid -g size=2
d.grid -g size=86:12
d.grid -g size=86:18

Hamish

[hamish]

btw, I just fixed d.grid + geogrid longitude label placement in all branches for meridians which deviated to grid-north by many degrees (e.g. zoomed-out LCC projections).

Hamish

[hamish]

new direction= option added in devbr6 r57699 to allow only drawing east-west or north-south grid lines. run the module twice with two different size intervals to get the custom effect. I'll try to find a few minutes to port it to g7 in the morning.

for drawing fiducial marks it would be better to have the size= option optionally take a second parameter, but I don't like overloading the parameter definition like that very much, and adding two new size_ew= and size_ns= options like g.region does for res= clutters the option list and Required-> parser setting, so isn't great either.

happy to entertain better ideas..

Hamish

[hamish]

merged into trunk in r57714.