1t.vect.algebra(1)             Grass User's Manual            t.vect.algebra(1)
2
3
4

NAME

6       t.vect.algebra   -  Apply temporal and spatial operations on space time
7       vector datasets using temporal vector algebra.
8

KEYWORDS

10       temporal, algebra, vector, time
11

SYNOPSIS

13       t.vect.algebra
14       t.vect.algebra --help
15       t.vect.algebra [-s] expression=expression  basename=basename   [--help]
16       [--verbose]  [--quiet]  [--ui]
17
18   Flags:
19       -s
20           Check  the  spatial topology of temporally related maps and process
21           only spatially related maps
22
23       --help
24           Print usage summary
25
26       --verbose
27           Verbose module output
28
29       --quiet
30           Quiet module output
31
32       --ui
33           Force launching GUI dialog
34
35   Parameters:
36       expression=expression [required]
37           Spatio-temporal mapcalc expression
38
39       basename=basename [required]
40           Basename of the new generated output maps
41           A numerical suffix separated by an underscore will be  attached  to
42           create a unique identifier
43

DESCRIPTION

45       t.vect.algebra  performs  temporal and spatial overlay and buffer func‐
46       tions on space time vector datasets (STVDS) by using the temporal  vec‐
47       tor  algebra. New STVDS can be created, which are expressions of exist‐
48       ing STVDS.
49
50   PROGRAM USE
51       The module expects an expression as input parameter  in  the  following
52       form:
53
54       "result = expression"
55       The  statement structure is similar to r.mapcalc, see r.mapcalc.  Where
56       result represents the name of a space time dataset  (STVDS)  that  will
57       contain  the  result  of the calculation that is given as expression on
58       the right side of the equality sign.  These expression can be any valid
59       or  nested  combination  of  temporal operations and functions that are
60       provided by the temporal vector algebra.
61       The algebra provides methods for map selection from STDS based on their
62       temporal  relations.  It  is also possible to temporally shift maps, to
63       create temporal buffer and to snap time instances  to  create  a  valid
64       temporal  topology. Furthermore expressions can be nested and evaluated
65       in conditional statements (if, else statements).  Within  if-statements
66       the  algebra provides temporal variables like start time, end time, day
67       of year, time differences or number of maps per time interval to  build
68       up  conditions. These operations can be assigned to space time datasets
69       or to the results of operations between space time datasets.
70
71       The type of the input space time datasets  must  be  defined  with  the
72       input  parameter type. Possible options are STRDS, STVDS or STR3DS. The
73       default is set to space time raster datasets (STRDS).
74
75       As default, topological relationships between space time datasets  will
76       be evaluated only temporal. Use the s flag to activate the additionally
77       spatial topology evaluation.
78
79       The expression option must be passed as quoted expression, for example:
80       t.select expression="C = A : B"
81       Where C is the new space time raster dataset  that  will  contain  maps
82       from  A that are selected by equal temporal relationships to the exist‐
83       ing dataset B in this case.
84

TEMPORAL VECTOR ALGEBRA

86       The temporal algebra provides a wide range of  temporal  operators  and
87       functions that will be presented in the following section.
88
89   TEMPORAL RELATIONS
90       Several  temporal  topology  relations between registered maps of space
91       time datasets are supported:
92       equals            A ------
93                         B ------
94       during            A  ----
95                         B ------
96       contains          A ------
97                         B  ----
98       starts            A ----
99                         B ------
100       started           A ------
101                         B ----
102       finishs           A   ----
103                         B ------
104       finished          A ------
105                         B   ----
106       precedes          A ----
107                         B     ----
108       follows           A     ----
109                         B ----
110       overlapped        A   ------
111                         B ------
112       overlaps          A ------
113                         B   ------
114       over              booth overlaps and overlapped
115       The relations must be read as: A is related to B, like - A equals B - A
116       is during B - A contains B
117
118       Topological relations must be specified in {} parentheses.
119
120   TEMPORAL OPERATORS
121       The  temporal  algebra  defines temporal operators that can be combined
122       with other operators to perform spatio-temporal operations. The  tempo‐
123       ral  operators process the time instances and intervals of two temporal
124       related maps and calculate the result temporal extent by five different
125       possibilities.
126       LEFT REFERENCE     l       Use the time stamp of the left space time dataset
127       INTERSECTION       i       Intersection
128       DISJOINT UNION     d       Disjoint union
129       UNION              u       Union
130       RIGHT REFERENCE    r       Use the time stamp of the right space time dataset
131
132   TEMPORAL SELECTION
133       The  temporal  selection  simply  selects parts of a space time dataset
134       without processing raster or  vector  data.   The  algebra  provides  a
135       selection  operator  :  that selects parts of a space time dataset that
136       are temporally equal to parts of a second one by default. The following
137       expression
138       C = A : B
139       means: Select all parts of space time dataset A that are equal to B and
140       store it in space time dataset C. The parts are time stamped maps.
141
142       In addition the inverse selection operator !: is defined as the comple‐
143       ment of the selection operator, hence the following expression
144       C = A !: B
145       means: select all parts of space time time dataset A that are not equal
146       to B and store it in space time dataset (STDS) C.
147
148       To select parts of a STDS by different topological relations  to  other
149       STDS,  the temporal topology selection operator can be used. The opera‐
150       tor consists of the temporal selection operator, the topological  rela‐
151       tions, that must be separated by the logical OR operator | and the tem‐
152       poral extent operator. All three parts are separated by comma and  sur‐
153       rounded by curly braces:
154       {"temporal selection operator", "topological relations", "temporal operator"}
155
156       Examples:
157       C = A {:, equals} B
158       C = A {!:, equals} B
159       We can now define arbitrary topological relations using the OR operator
160       "|" to connect them:
161       C = A {:,equals|during|overlaps} B
162       Select all parts of A that are equal to B, during B or overlaps B.
163       In addition we can define the temporal extent of  the  result  STDS  by
164       adding the temporal operator.
165       C = A {:, during,r} B
166       Select  all  parts  of A that are during B and use the temporal extents
167       from B for C.
168
169       The selection operator is implicitly contained in the temporal topology
170       selection  operator,  so  that the following statements are exactly the
171       same:
172       C = A : B
173       C = A {:} B
174       C = A {:,equal} B
175       C = A {:,equal,l} B
176       Same for the complementary selection:
177       C = A !: B
178       C = A {!:} B
179       C = A {!:,equal} B
180       C = A {!:,equal,l} B
181
182   CONDITIONAL STATEMENTS
183       Selection operations can be evaluated within conditional statements.
184       Note A and B can either be space time datasets or expressions. The tem‐
185       poral  relationship  between  the conditions and the conclusions can be
186       defined at the beginning of the if statement. The relationship  between
187       then and else conclusion must be always equal.
188       if statement                           decision option                        temporal relations
189         if(if, then, else)
190         if(conditions, A)                    A if conditions are True;              temporal topological relation between if and then is equal.
191         if(conditions, A, B)                 A if conditions are True, B otherwise; temporal topological relation between if, then and else is equal.
192         if(topologies, conditions, A)        A if conditions are True;              temporal topological relation between if and then is explicit specified by topologies.
193         if(topologies, conditions, A, B)     A if conditions are True, B otherwise; temporal topological relation between if, then and else is explicit specified by topologies.
194
195   Logical operators
196       Symbol  description
197         ==    equal
198         !=    not equal
199         >     greater than
200         >=    greater than or equal
201         <     less than
202         <=    less than or equal
203         &&    and
204         ||    or
205
206   Temporal functions
207       The  following  temporal  function are evaluated only for the STDS that
208       must be given in parenthesis.
209       td(A)                    Returns a list of time intervals of STDS A
210       start_time(A)            Start time as HH::MM:SS
211       start_date(A)            Start date as yyyy-mm-DD
212       start_datetime(A)        Start datetime as yyyy-mm-DD HH:MM:SS
213       end_time(A)              End time as HH:MM:SS
214       end_date(A)              End date as yyyy-mm-DD
215       end_datetime(A)          End datetime as  yyyy-mm-DD HH:MM
216       start_doy(A)             Day of year (doy) from the start time [1 - 366]
217       start_dow(A)             Day of week (dow) from the start time [1 - 7], the start of the week is Monday == 1
218       start_year(A)            The year of the start time [0 - 9999]
219       start_month(A)           The month of the start time [1 - 12]
220       start_week(A)            Week of year of the start time [1 - 54]
221       start_day(A)             Day of month from the start time [1 - 31]
222       start_hour(A)            The hour of the start time [0 - 23]
223       start_minute(A)          The minute of the start time [0 - 59]
224       start_second(A)          The second of the start time [0 - 59]
225       end_doy(A)               Day of year (doy) from the end time [1 - 366]
226       end_dow(A)               Day of week (dow) from the end time [1 - 7], the start of the week is Monday == 1
227       end_year(A)              The year of the end time [0 - 9999]
228       end_month(A)             The month of the end time [1 - 12]
229       end_week(A)              Week of year of the end time [1 - 54]
230       end_day(A)               Day of month from the start time [1 - 31]
231       end_hour(A)              The hour of the end time [0 - 23]
232       end_minute(A)            The minute of the end time [0 - 59]
233       end_second(A)            The second of the end time [0 - 59]
234
235   Comparison operator
236       The conditions are comparison expressions that  are  used  to  evaluate
237       space time datasets. Specific values of temporal variables are compared
238       by logical operators and evaluated for each map of  the  STDS  and  the
239       related  maps.   For  complex  relations the comparison operator can be
240       used to combine conditions:
241       The structure is similar to the select operator with the  extension  of
242       an aggregation operator:
243       {"comparison operator", "topological relations", aggregation operator, "temporal operator"}
244       This  aggregation  operator  (|  or &) define the behaviour if a map is
245       related the more than one map, e.g for the topological relations  ’con‐
246       tains’.   Should  all (&) conditions for the related maps be true or is
247       it sufficient to have any (|) condition that  is  true.  The  resulting
248       boolean value is then compared to the first condition by the comparison
249       operator (|| or &&).  As default the aggregation operator is related to
250       the comparison operator:
251       Comparison operator -> aggregation operator:
252       || -> | and && -> &
253       Examples:
254       Condition 1 {||, equal, r} Condition 2
255       Condition 1 {&&, equal|during, l} Condition 2
256       Condition 1 {&&, equal|contains, |, l} Condition 2
257       Condition 1 {&&, equal|during, l} Condition 2 && Condition 3
258       Condition 1 {&&, equal|during, l} Condition 2 {&&,contains, |, r} Condition 3
259
260   Hash operator
261       Additionally  the  number of maps in intervals can be computed and used
262       in conditional statements with the hash (#) operator.
263       A{#, contains}B
264       This expression computes the number of maps from space time  dataset  B
265       which are during the time intervals of maps from space time dataset A.
266       A  list  of integers (scalars) corresponding to the maps of A that con‐
267       tain maps from B will be returned.
268
269       C = if({equal}, A {#, contains} B > 2, A {:, contains} B)
270       This expression selects all maps from A  that  temporally  contains  at
271       least  2 maps from B and stores them in space time dataset C. The lead‐
272       ing equal statement in the if condition specifies the temporal relation
273       between  the if and then part of the if expression. This is very impor‐
274       tant, so we do not need to specify a global  time  reference  (a  space
275       time dataset) for temporal processing.
276
277       Furthermore  the  temporal  algebra allows temporal buffering, shifting
278       and snapping with the functions buff_t(), tshift() and tsnap()  respec‐
279       tively.
280       buff_t(A, size)         Buffer STDS A with granule ("1 month" or 5)
281       tshift(A, size)         Shift STDS A with granule ("1 month" or 5)
282       tsnap(A)                Snap time instances and intervals of STDS A
283
284   Single map with temporal extent
285       The  temporal  algebra  can also handle single maps with time stamps in
286       the tmap function.
287       tmap()
288       For example:
289        C = A {:,during} tmap(event)
290       This statement select all maps from space time data set A that are dur‐
291       ing the temporal extent of single map ’event’
292
293   Spatial vector operators
294       The module supports the following boolean vector operations:
295        Boolean Name   Operator Meaning         Precedence   Correspondent function
296       ----------------------------------------------------------------------------------
297        AND            &        Intersection          1      (v.overlay operator=and)
298        OR             |        Union                 1      (v.overlay operator=or)
299        DISJOINT OR    +        Disjoint union        1      (v.patch)
300        XOR            ^        Symmetric difference  1      (v.overlay operator=xor)
301        NOT            ~        Complement            1      (v.overlay operator=not)
302       And vector functions:
303        buff_p(A, size)           Buffer the points of vector map layer A with size
304        buff_l(A, size)           Buffer the lines of vector map layer A with size
305        buff_a(A, size)           Buffer the areas of vector map layer A with size
306
307   Combinations of temporal, vector and select operators
308       We  combine the temporal topology relations, the temporal operators and
309       the spatial/select operators to create  spatio-temporal  vector  opera‐
310       tors:
311       {"spatial or select operator" , "list of temporal relations", "temporal operator" }
312
313       For  multiple  topological  relations  or several related maps the spa‐
314       tio-temporal operators feature implicit aggregation.  The algebra eval‐
315       uates  the stated STDS by their temporal topologies and apply the given
316       spatio temporal operators in a aggregated form.  If we have two STDS  A
317       and  B,  B  has three maps: b1, b2, b3 that are all during the temporal
318       extent of the single map a1 of A, then the following  overlay  calcula‐
319       tions  would implicitly aggregate all maps of B into one result map for
320       a1 of A:
321       C = A {&, contains} B --> c1 = a1 & b1 & b2 & b3
322       Keep attention that the aggregation behaviour is not symmetric:
323       C = B {&, during} A --> c1 = b1 & a1
324                               c2 = b2 & a1
325                               c3 = b3 & a1
326
327   Examples:
328       Spatio-temporal intersect all maps from space time dataset A  with  all
329       maps  from  space  time  dataset B which have equal time stamps and are
330       temporary before Jan. 1. 2005 and store them in space time dataset D.
331       D = if(start_date(A) < "2005-01-01", A & B)
332       Buffer all vector points from space time vector dataset A and B with  a
333       distance of one and intersect the results with overlapping, containing,
334       during and equal temporal relations to store the result in  space  time
335       vector dataset D with intersected time stamps.
336       D = buff_p(A, 1) {&,overlaps|overlapped|equal|during|contains,i} buff_p(B, 1)
337       Select all maps from space time dataset B which are during the temporal
338       buffered space time dataset A with a map interval of three  days,  else
339       select maps from C and store them in space time dataset D.
340       D = if(contains, td(buff_t(A, "1 days")) == 3, B, C)
341

REFERENCES

343       PLY(Python-Lex-Yacc)
344

SEE ALSO

346        t.select
347

AUTHORS

349       Thomas  Leppelt,  Soeren  Gebbert,  Thünen  Institute of Climate-Smart
350       Agriculture
351

SOURCE CODE

353       Available at: t.vect.algebra source code (history)
354
355       Main index | Temporal index | Topics index | Keywords index | Graphical
356       index | Full index
357
358       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
359
360
361
362GRASS 7.8.2                                                  t.vect.algebra(1)
Impressum