1v.lrs.create(1) Grass User's Manual v.lrs.create(1)
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6 v.lrs.create - Create Linear Reference System
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9 vector, LRS, networking
10
12 v.lrs.create
13 v.lrs.create help
14 v.lrs.create in_lines=name out_lines=name [err=name] points=name
15 [llayer=integer] [player=integer] lidcol=string pidcol=string
16 [start_mp=string] [start_off=string] [end_mp=string]
17 [end_off=string] rstable=string [thresh=float] [--overwrite]
18 Flags:
20 --overwrite
21 Parameters:
23 in_lines=name
24 Input vector map containing lines
25 out_lines=name
27 Output vector map where oriented lines are written
28 err=name
30 Output vector map of errors
31 points=name
33 Input vector map containing reference points
34 llayer=integer
36 Line layer Default: 1
37 player=integer
39 Point layer Default: 1
40 lidcol=string
42 Column containing line identifiers for lines
43 pidcol=string
45 Column containing line identifiers for points
46 start_mp=string
48 Column containing milepost position for the beginning of next seg‐
49 ment Default: start_mp
50 start_off=string
52 Column containing offset from milepost for the beginning of next
53 segment Default: start_off
54 end_mp=string
56 Column containing milepost position for the end of previous segment
57 Default: end_mp
58 end_off=string
60 Column containing offset from milepost for the end of previous seg‐
61 ment Default: end_off
62 rstable=string
64 Name of table where the reference system will be written New table
65 is created by this module
66 thresh=float
68 Maximum distance of point to line allowed Default: 1
69
71 v.lrs.create generates a LRS (Linear Reference System) from vector line
72 and point data.
73 It is highly recommended to work with polylines instead of segmented
75 vector lines. The command v.build.polylines creates this map structure.
76
78 The mileposts (point) vector map columns start_mp, start_off, end_mp,
79 end_off must be of 'double precision' type. For milepost ordering, it
80 is sufficient to enter increasing numbers into the start_mp column
81 indicating the order along the vector line.
82 The lidcol and pidcol columns contain the line IDs which relate mile‐
84 posts and vector line(s) to each other.
85 When creating a LRS with this module, any existing rstable will be
87 replaced.
88
90 This example is written for the Spearfish dataset.
91 As first step, bus route data are prepared.
93 # copy into own mapset
94 g.copy roads_net,busroute_tmp
95 d.mon x0
96 d.vect busroute_tmp
97 # zoom to Spearfish (nord-west city)
98 d.zoom
99 # reduce route map to bus route (reduce to one line)
100 d.extract busroute_tmp out=busroute_tmp2
101 # vector line needs to be polyline
102 v.build.polylines busroute_tmp2 out=busroute_tmp3
103 v.category busroute_tmp3 out=busroute op=add
104 g.remove vect=busroute_tmp,busroute_tmp2,busroute_tmp3
105 The result can be visualized:
106 g.region vect=busroute n=n+100 s=s-100 w=w-100 e=e+100
107 d.mon x0
108 d.vect roads_net
109 d.vect busroute col=red width=2
110 The vector map 'busroute' needs have an attribute table which contain
111 an integer column lidcol with value be '22' for this example (bus
112 route):
113 v.db.addtable busroute col="lid integer"
114 v.db.update busroute col=lid value=22
115 v.db.select busroute
116 cat|lid
117 1|22
118 A new point map 'busstops' shall contain mileposts (bus stops) along
119 this line (use thresh to define maximal accepted deviation from this
120 line):
121 # generate points map
122 # use d.where to find coordinates along the bus route
123 # use v.in.ascii out=busstops to generate map
124 d.vect busstops icon=basic/triangle col=blue
125 d.vect busstops disp=cat lcol=blue
126 The milepost attributes table needs to be created with specific col‐
127 umns:
128 v.db.addtable busstops col="lid integer, start_mp double precision, \
129 start_off double precision, end_mp double precision, \
130 end_off double precision"
131 v.db.update busstops col=lid value=22
132 Since the digitizing order of v.in.ascii above reflects the bus stop
133 order along the route, we can simply copy the category number as mile‐
134 post order number in column start_mp:
135 v.db.update busstops col=start_mp qcol=cat
136 # verify table
137 v.db.select busstops
138 cat|lid|start_mp|start_off|end_mp|end_off
139 1|22|1|||
140 2|22|2|||
141 3|22|3|||
142 4|22|4|||
143 5|22|5|||
144 6|22|6|||
145 7|22|7|||
146 # visualize with start_mp to check order
147 d.erase
148 d.vect roads_net
149 d.vect busroute col=red width=2
150 d.vect busstops icon=basic/triangle col=blue
151 d.vect busstops disp=attr attrcol=start_mp lcol=blue
152 Offsets (start_off, end_off) can be later used in case the route or
153 mileposts get modified.
154 As second step, the linear reference network is created:
156 v.lrs.create busroute points=busstops out=route_lrs err=lrs_error \
157 lidcol=lid pidcol=lid rstable=route_lrs thresh=50
158 This creates the maps 'route_lrs' containing the LRS and 'lrs_error'
159 containing the errors if any. The resulting LRS table and map can be
160 shown:
161 # show LRS table
162 db.select route_lrs
163 d.vect route_lrs col=blue width=2
164
167 LRS tutorial,
168 Introducing the Linear Reference System in GRASS,
169 v.build.polylines, v.lrs.segment, v.lrs.where, v.lrs.label
171
173 Radim Blazek, ITC-irst/MPA Solutions
174 Documentation update (based on above journal article and available
175 fragments): Markus Neteler
176 Last changed: $Date: 2007/06/28 15:42:47 $
178 Full index
180GRASS 6.2.2 v.lrs.create(1)