GRIDS and Graticule

[Jeff de La Beaujardiere]

François TOURDE wrote:
> It seems that the {MIN|MAX}{ARCS|INTERVALS|SUBDIVIDE} parameters
> doesn't works correctly on my .map file.

I finally figured out how to configure this properly: instead of trying 
a combination of several of these parameters, use only the ONE parameter 
that produces the desired effect. For example, if you want a fixed grid 
at some interval, then specify MININTERVAL. If you want a reasonable 
number of lines no matter what the zoom, specify MINARCS. (I have found 
that 'MINARCS 5' and 'LABELFORMAT DDMM' gives good results for 
geographic coordinates.

If you look in the source code mapfile.c, the function loadGrid has a 
switch statement such that only the first matching directive is used. 
They appear in this order:

MINARCS
MAXARCS
MININTERVAL
MAXINTERVAL
MINSUBDIVIDE
MAXSUBDIVIDE

The documentation at 
http://mapserver.gis.umn.edu/doc44/mapfile-reference.html#grid should be 
corrected because it gives a false impression. It should say something 
like this:

<quote>
The number of arcs to draw is controlled by any ONE of the following 
parameters.  Mapserver will inspect the GRID object and search for these 
parameters in this order and will obey the first one it finds:

MINARCS [double]

     The minimum number of arcs to draw in the bounding box.

MAXARCS [double]

     The maximum number of arcs to draw in the bounding box. [NOT TESTED]

MININTERVAL [double]

     The interval between gridlines, independent of bounding box size.

MAXINTERVAL [double]

     The interval between gridlines, independent of bounding box size. 
No discernible difference between MININTERVAL and MAXINTERVAL.

MINSUBDIVIDE [double]

     The minimum number of segments to use when rendering an arc.  [NOT 
TESTED]

MAXSUBDIVIDE [double]

     The maximum number of segments to use when rendering an arc.  [NOT 
TESTED]
</quote>


-Jeff DLB