[GRASS-user] re-order boundaries by relative position along polyline

Thu Apr 2 15:31:24 PDT 2015

Hi,

Once again, I am reminded that complex spatial analysis in other software
can usually be reduced to a couple of lines of code in GRASS-- thanks!

Here is a fun question. Suppose you have a set of line segments, or
boundaries that are the result of a digitizing process that generated
segments out of "order":

      2             4              1           3
O---------+-----------------+------------+------O

'O' = start / end point
'+' = vertex

... in this case "order" is associated with order in which records appear
in the attribute table and the order in which segments are drawn on the
screen.

Is there a module, or set of modules that could be used to re-order the
segments so that the order of records in the attribute table and drawing
order is:

      1             2              3           4
O---------+-----------------+------------+------O

Note that I do not wan't to shuffle the linkages between geometry and
attributes, rather, I would like to re-order the segments and attribute
table according to the linear position within the set of contiguous
boundaries or polyline.

Here is an example set of lines in ASCII format, WGS84 GCS.

ORGANIZATION:
DIGIT DATE:
DIGIT NAME:   dylan
MAP NAME:
MAP DATE:     Thu Apr  2 11:46:34 2015
MAP SCALE:    1
OTHER INFO:
ZONE:         0
MAP THRESH:   0.000000
VERTI:
B  6 1
 -118.71960108 36.71846736
 -118.71946261 36.71783146
 -118.71905508 36.71717314
 -118.71863837 36.71610377
 -118.71807413 36.71546352
 -118.71786286 36.71527706
 2     132
B  3 1
 -118.7153795 36.73403608
 -118.71537992 36.73272737
 -118.71538933 36.73177277
 2     133
B  3 1
 -118.71536851 36.76205202
 -118.7153724 36.7609144
 -118.71537619 36.75980591
 2     150
B  2 1
 -118.73128842 36.69749903
 -118.73130166 36.69760244
 2     175
B  5 1
 -118.71538933 36.73177277
 -118.7153944 36.73125742
 -118.71573607 36.73044156
 -118.71618977 36.72875872
 -118.71651025 36.72811846
 2     581
B  15 1
 -118.71651025 36.72811846
 -118.71661716 36.72766138
 -118.71660977 36.7273294
 -118.71645785 36.72668322
 -118.71689758 36.7261392
 -118.71724087 36.72567564
 -118.71747107 36.7248177
 -118.71753527 36.72390024
 -118.71787045 36.72307308
 -118.71797278 36.72237579
 -118.71781832 36.72073331
 -118.71825483 36.72004703
 -118.71908689 36.71948153
 -118.71963768 36.71863545
 -118.71960108 36.71846736
 2     602
B  8 1
 -118.7180943 36.70872005
 -118.71827421 36.7083356
 -118.71841915 36.7080259
 -118.7190169 36.70752707
 -118.72008403 36.70694237
 -118.72042476 36.70636815
 -118.72049695 36.70608245
 -118.7212077 36.70547966
 2     604
B  15 1
 -118.7212077 36.70547966
 -118.721692  36.70506892
 -118.72256889 36.70442599
 -118.72372477 36.702873
 -118.72417965 36.70213899
 -118.72496002 36.70190631
 -118.72660809 36.70183505
 -118.72765407 36.70118732
 -118.72831767 36.70100376
 -118.72866574 36.7007615
 -118.72887421 36.70026501
 -118.72998965 36.69849669
 -118.73066541 36.69798083
 -118.73118943 36.69770441
 -118.73130166 36.69760244
 2     609
B  8 1
 -118.7153867 36.75138736
 -118.7153804 36.7500365
 -118.7153634 36.7464107
 -118.7153465 36.742785
 -118.7153296 36.7391593
 -118.71533791 36.73753527
 -118.7153438 36.7363838
 -118.7153795 36.73403608
 2     610
B  13 1
 -118.71786286 36.71527706
 -118.71763335 36.71507451
 -118.71748992 36.71480774
 -118.71754381 36.71369999
 -118.71750723 36.7131568
 -118.71786592 36.71228789
 -118.71745106 36.71129755
 -118.71716489 36.71079564
 -118.71709787 36.71043286
 -118.71712906 36.71006868
 -118.71740871 36.70978478
 -118.717644  36.709369
 -118.7180943 36.70872005
 2     612
B  7 1
 -118.71411256 36.77582538
 -118.71445897 36.77550631
 -118.71478471 36.77508229
 -118.7149828 36.77446623
 -118.71532537 36.77406797
 -118.7153339 36.7717931
 -118.71534777 36.76808916
 2     613
B  3 1
 -118.71534777 36.76808916
 -118.71536   36.7645405
 -118.71536851 36.76205202
 2     622
B  4 1
 -118.71537619 36.75980591
 -118.7153848 36.7572883
 -118.7153973 36.7536622
 -118.7153867 36.75138736
 2     623

I have been able to convert these segments into polylines, however, I am
not sure how one would go about computing the position along the polylines.
Perhaps a linear referencing system?

Thanks!
Dylan