Changes between Version 6 and Version 7 of Grass7/TemporalGISAlgebra

Timestamp:

Jul 5, 2013, 6:08:09 AM (11 years ago)

Author:

huhabla

Comment:

--

Grass7/TemporalGISAlgebra

@@ -28 +28 @@
 Hence many operations that are common in spatial processing should have an equivalent in the temporal processing.
 
+==== Temporal selection ====
+
 Here an example of the temporal algebra that simply selects parts of a space time dataset without the processing raster or vector data:
 
@@ -48 +50 @@
 }}}
 
-We can now define arbitrary topological relations using logical or || to connect them:
+We can now define arbitrary topological relations using logical OR to connect them:
 
 {{{
@@ -56 +58 @@
 Select all parts of A that are equal B, during B or overlaps B.
 
-In addition we define a temporal buffer function, that buffer time instances or time intervals:
-
+In addition we define a temporal functions:
+
+==== Temporal buffer ====
+Buffer time instances or time intervals:
+{{{
 buff_t(STDS, "time interval")
-
+}}}
 Example:
-
 {{{
 C = buff_t(A, "1 day")
@@ -67 +71 @@
 
 Buffer all maps of STDS A with a temporal buffer of one day.
+
+==== Temporal shift ====
+
+Temporally shift all maps in a space time dataset by an interval:
+{{{
+tshift(STDS, "time interval")
+}}}
+Example:
+{{{
+tshift(A, "2 months")
+}}}
+Temporally shift all maps of space time dataset A by two months.
+
+==== Temporally snap ===
+
+Temporally snap time instances to its temporal nearest neighbor in the future and close gaps between time intervals.
+{{{
+tsnap(STDS)
+}}}
+
+==== The hash operator ====
+
+It is of important interest how many maps are located in the time interval of a single map when processing two space time datasets.
+For this reason the hash operator '''#''' was introduced. In addition to the hash operator the temporal relation can be specified 
+that should be analysed.
+
+Example:
+{{{
+C = if(equal, A{contains,#}B > 2, A{contains,:}B)
+}}}
+This expression selects all maps from A that temporally contains at least 2 maps from B and stores them in space time dataset C.
+The leading '''equal''' statement in the '''if''' condition specifies the temporal relation between the if and then part of the expression. This is very important, so we do not need to specify a time reference for temporal processing.
 = Overview of all temporal algebra elements =