Re: [Matplotlib-users] basemap scalebar

[Jeff W. <js...@fa...>]

Michael Hearne wrote:
> Jeff - That would replicate the "simple" scale-bar from GMT.  Below is 
> my not-complete attempt at replicating the "fancy" scale bar.  It 
> would need some options for specifying different units (miles, 
> nautical miles, etc.) and perhaps some more attention to spacing of 
> the text from the scale bar and tick marks...
>
> --Mike

Mike:  Very nice!  Do you want the scale to show the true distance on 
the earth (in which case the labels will vary depending on where the 
label is placed), or the distance in map projection coordinates (in 
which case the labels are constant)?  Or perhaps a lat/lon value could 
be given to specify where the scale is true?

-Jeff
>
> from numpy import *
> from matplotlib.toolkits.basemap import Basemap, pyproj
> from pylab import *
> # add drawscale method to Basemap class.
> class Basemap2(Basemap):
>    def drawscale(self,lon,lat,length,yoffset=None):
>        """draw a fancy map scale from lon-length/2,lat-yoffset to
>        lon-length/2,lat-yoffset, label it with actual distance in km"""
>        length = length*1000 #input length is km
>
>        #we need 5 sets of x coordinates (in map units)
>        #center of scale
>        xc,yc = self(lon,lat)
>        #left edge of scale
>        lon1,lat1 = self(xc-length/2,yc,inverse=True)
>        x1,y1 = self(lon1,lat1)
>        #quarter scale
>        lon2,lat2 = self(xc-length/4,yc,inverse=True)
>        x2,y2 = self(lon2,lat2)
>        #three quarter scale
>        lon3,lat3 = self(xc+length/4,yc,inverse=True)
>        x3,y3 = self(lon3,lat3)
>        #right edge of scale
>        lon4,lat4 = self(xc+length/2,yc,inverse=True)
>        x4,y4 = self(lon4,lat4)
>        
>        if yoffset is None: yoffset = 0.1*length
>
>        #plot top line
>        ytop = yc+yoffset/2
>        ybottom = yc-yoffset/2
>        ytick = ybottom - yoffset/2
>        ytext = ytick - yoffset/2
>        m.plot([x1,x4],[ytop,ytop],color='k')
>        #plot bottom line
>        m.plot([x1,x4],[ybottom,ybottom],color='k')
>        #plot left edge
>        m.plot([x1,x1],[ybottom,ytop],color='k')
>        #plot right edge
>        m.plot([x4,x4],[ybottom,ytop],color='k')
>
>        #make a filled black box from left edge to 1/4 way across
>        fill([x1,x2,x2,x1,x1],[ytop,ytop,ybottom,ybottom,ytop],'k')
>        #make a filled white box from 1/4 way across to 1/2 way across
>        fill([x2,xc,xc,x2,x2],[ytop,ytop,ybottom,ybottom,ytop],'w')
>        #make a filled white box from 1/2 way across to 3/4 way across
>        fill([xc,x3,x3,xc,xc],[ytop,ytop,ybottom,ybottom,ytop],'k')
>        #make a filled white box from 3/4 way across to end
>        fill([x3,x4,x4,x3,x3],[ytop,ytop,ybottom,ybottom,ytop],'w')
>        
>        #plot 3 tick marks at left edge, center, and right edge
>        m.plot([x1,x1],[ytick,ybottom],color='k')
>        m.plot([xc,xc],[ytick,ybottom],color='k')
>        m.plot([x4,x4],[ytick,ybottom],color='k')
>
>        #label 3 tick marks
>        text(x1,ytext,'%d' % (0),\
>    horizontalalignment='center',\
>    verticalalignment='top',\
>    fontsize=9)
>        text(xc,ytext,'%d' % (round((length/2)/1000)),\
>    horizontalalignment='center',\
>    verticalalignment='top',\
>    fontsize=9)
>        text(x4,ytext,'%d' % (round((length)/1000)),\
>    horizontalalignment='center',\
>    verticalalignment='top',\
>    fontsize=9)
>
>        #put units on top
>        text(xc,ytop+yoffset/2,'km',\
>    horizontalalignment='center',\
>    verticalalignment='bottom',\
>    fontsize=9)
>
> # setup of basemap ('lcc' = lambert conformal conic).
> # use major and minor sphere radii from WGS84 ellipsoid.
> m = 
> Basemap2(llcrnrlon=-145.5,llcrnrlat=1.,urcrnrlon=-2.566,urcrnrlat=46.352,\
>      rsphere=(6378137.00,6356752.3142),\
>      resolution='l',area_thresh=1000.,projection='lcc',\
>      lat_1=50.,lon_0=-107.)
> # draw coastlines and political boundaries.
> m.drawcoastlines()
> m.fillcontinents()
> # draw parallels and meridians.
> # label on left, right and bottom of map.
> m.drawparallels(arange(0.,80,20.),labels=[1,1,0,1])
> m.drawmeridians(arange(10.,360.,30.),labels=[1,1,0,1])
> # draw a line from x1,y to x2,y and label it with distance in km.
> length = 3000 #kilometers
> x1,y1 = 0.25*m.xmax, 0.25*m.ymax
> lon1,lat1 = m(x1,y1,inverse=True)
> m.drawscale(lon1,lat1,length)
> title('a fancy map scale')
> show()
>
>
>
>
> ------------------------------------------------------
> Michael Hearne
> mh...@us... <mailto:mh...@us...>
> (303) 273-8620
> USGS National Earthquake Information Center
> 1711 Illinois St. Golden CO 80401
> Senior Software Engineer
> Synergetics, Inc.
> ------------------------------------------------------
>
>


-- 
Jeffrey S. Whitaker         Phone : (303)497-6313
NOAA/OAR/CDC  R/PSD1        FAX   : (303)497-6449
325 Broadway                Boulder, CO, USA 80305-3328