[GRASS-dev] [bug #5454] (grass) ps.map scaling not correct when projection units are feet

[Hamish Bowman via RT]

this bug's URL: http://intevation.de/rt/webrt?serial_num=5454

Request number 5454 was commented on by 'hbowman' (Hamish Bowman). 
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Cc: grass-dev at grass.itc.it

here it is:

ps.map/map_setup.c

    /* set the scale */
    if (!PS.scaletext[0]) sprintf(PS.scaletext, "1 : %.0f",
	39.37 * 72.0 * (PS.w.east - PS.w.west) / PS.map_pix_wide);

that assumes east-west is in meters. It should be using the distance()
fn to return distance in meters like ps.map/scale.c does.

39.37 is meters->inches; 72.0 is inches to PostScript units (points, as
in font size of 10 is 10/72" tall when printed)



do_scalebar.c was assuming input segment length was in meters too.

should be:

    /* convert scale size to map inches */
    length = (sb.length / scale_size) *
	G_database_units_to_meters_factor() * METERS_TO_INCHES;


This could very well be what is breaking the scale for lat/lon:
   http://intevation.de/rt/webrt?serial_num=3096
(although due to curvature that will never be correct for both dims)



Hamish



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