| Type: | Package |
| Title: | Trend Classification Algorithm |
| Version: | 1.3 |
| Date: | 2026-10-20 |
| Description: | Classifies trends as linear, quadratic, cubic, concealed, or no-trend. Concealed trends have a quadratic or cubic form, but their net change between the beginning and end of the time period is not statistically significant. The no-trend category includes linear trends with a statistically insignificant slope. The method is described in Jamali et al. (2014) <doi:10.1016/j.rse.2013.10.019>. |
| License: | GPL-2 |
| Encoding: | UTF-8 |
| NeedsCompilation: | no |
| Packaged: | 2026-10-22 07:27:31 UTC; sadegh |
| Author: | Sadegh Jamali [aut, cre], Hristo Tomov [aut] |
| Maintainer: | Sadegh Jamali <sadegh.jamali@tft.lth.se> |
| Repository: | CRAN |
| Date/Publication: | 2026-11-04 10:10:08 UTC |
Trend Classification Algorithm
Description
PolyTrend classifies the trends into linear, quadratic, cubic, concealed and no-trend types. The "concealed trends" are those trends that possess quadratic or cubic forms, but the net change from the start of the time period to the end of the time period hasn't been significant. The "no-trend" category includes simple linear trends with statistically in-significant slope coefficient.
Usage
PolyTrend(Y, alpha)
Arguments
Y |
a vector of values corresponding to the trend or de-seasonalised component of vegetation time series data. |
alpha |
the statistical significance level. |
Details
An object of the class "PT" is a list including the trend type, slope, direction, and statistical significance.
Value
TrendType |
the trend type as a number, which can be -1, 0, 1, 2, or 3. The values correspond to a concealed trend (-1), no trend (0), linear trend (1), quadratic trend (2) or cubic trend (3). |
Slope |
the linear slope value. |
Direction |
the linear slope direction as a number, which can be 1 or -1. The values correspond to increasing (1) or decreasing direction (-1). |
Significance |
the slope significance as a number, which can be 1 or -1. The values correspond to statistically significant (1) or statistically in-significant (-1). |
PolynomialDegree |
the polynomial degree as a number, which can be 0, 1, 2, or 3. The values correspond to no-trend (0), linear (1), quadratic (2), or cubic (3). |
Author(s)
Sadegh Jamali, Hristo Tomov
References
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Tomov H (2016). Automated temporal NDVI analysis over the Middle East for the period 1982 – 2010. http://lup.lub.lu.se/student-papers/record/8871893
Examples
## Following examples are taken from Fig. 3 in Jamali et al. 2014
## Examples of a cubic trend (Site 1 & Site 2)
data(ex.a)
data(ex.b)
pt.a <- PolyTrend(ex.a, 0.05)
plot(pt.a, fig.dates = c(1982:2006))
pt.b <- PolyTrend(ex.b, 0.05)
plot(pt.b, fig.dates = c(1982:2006))
## Examples of a concealed trend with cubic form (Site 3 & Site 4)
data(ex.c)
data(ex.d)
pt.c <- PolyTrend(ex.c, 0.05)
plot(pt.c, fig.dates = c(1982:2006))
pt.d <- PolyTrend(ex.d, 0.05)
plot(pt.d, fig.dates = c(1982:2006))
## Examples of a quadratic trend (Site 5 & Site 6)
data(ex.e)
data(ex.f)
pt.e <- PolyTrend(ex.e, 0.05)
plot(pt.e, fig.dates = c(1982:2006))
pt.f <- PolyTrend(ex.f, 0.05)
plot(pt.f, fig.dates = c(1982:2006))
## Examples of a concealed trend with quadratic form (Site 7 & Site 8)
data(ex.g)
data(ex.h)
pt.g <- PolyTrend(ex.g, 0.05)
plot(pt.g, fig.dates = c(1982:2006))
pt.h <- PolyTrend(ex.h, 0.05)
plot(pt.h, fig.dates = c(1982:2006))
## Examples of a linear trend (Site 9 & Site 10)
data(ex.k)
data(ex.m)
pt.k <- PolyTrend(ex.k, 0.05)
plot(pt.k, fig.dates = c(1982:2006))
pt.m <- PolyTrend(ex.m, 0.05)
plot(pt.m, fig.dates = c(1982:2006))
## Example of a no-trend (Site 11)
data(ex.n)
pt.n <- PolyTrend(ex.n, 0.05)
plot(pt.n, fig.dates = c(1982:2006))
Site 1
Description
Example of a cubic trend (Site 1, Jamali et al. 2014)
Usage
data("ex.a")Format
The format is: num [1:25] 0.477 0.526 0.52 0.571 0.554 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.a)
## maybe str(ex.a) ; plot(ex.a) ...
Site 2
Description
Example of a cubic trend (Site 2, Jamali et al. 2014)
Usage
data("ex.b")Format
The format is: num [1:25] 0.254 0.267 0.184 0.22 0.208 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.b)
## maybe str(ex.b) ; plot(ex.b) ...
Site 3
Description
Example of a concealed trend with cubic form (Site 3, Jamali et al. 2014)
Usage
data("ex.c")Format
The format is: num [1:25] 0.712 0.726 0.736 0.723 0.739 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.c)
## maybe str(ex.c) ; plot(ex.c) ...
Site 4
Description
Example of a concealed trend with cubic form (Site 4, Jamali et al. 2014)
Usage
data("ex.d")Format
The format is: num [1:25] 0.6 0.54 0.447 0.478 0.457 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.d)
## maybe str(ex.d) ; plot(ex.d) ...
Site 5
Description
Example of a quadratic trend (Site 5, Jamali et al. 2014)
Usage
data("ex.e")Format
The format is: num [1:25] 0.26 0.278 0.196 0.224 0.261 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.e)
## maybe str(ex.e) ; plot(ex.e) ...
Site 6
Description
Example of a quadratic trend (Site 6, Jamali et al. 2014)
Usage
data("ex.f")Format
The format is: num [1:25] 0.327 0.259 0.212 0.298 0.248 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.f)
## maybe str(ex.f) ; plot(ex.f) ...
Site 7
Description
Example of a concealed trend with quadratic form (Site 7, Jamali et al. 2014)
Usage
data("ex.g")Format
The format is: num [1:25] 0.147 0.153 0.104 0.123 0.15 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.g)
## maybe str(ex.g) ; plot(ex.g) ...
Site 8
Description
Example of a concealed trend with quadratic form (Site 8, Jamali et al. 2014)
Usage
data("ex.h")Format
The format is: num [1:25] 0.813 0.809 0.753 0.792 0.727 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.h)
## maybe str(ex.h) ; plot(ex.h) ...
Site 9
Description
Example of a linear trend (Site 9, Jamali et al. 2014)
Usage
data("ex.k")Format
The format is: num [1:25] 0.382 0.373 0.228 0.385 0.271 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.k)
## maybe str(ex.k) ; plot(ex.k) ...
Site 10
Description
Example of a linear trend (Site 10, Jamali et al. 2014)
Usage
data("ex.m")Format
The format is: num [1:25] 0.781 0.738 0.795 0.871 0.736 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.m)
## maybe str(ex.m) ; plot(ex.m) ...
Site 11
Description
Example of a no-trend (Site 11, Jamali et al. 2014)
Usage
data("ex.n")Format
The format is: num [1:25] 0.567 0.625 0.61 0.589 0.569 ...
Source
Jamali S, Seaquist J, Eklundh L, Ardö J (2014). Automated mapping of vegetation trends with polynomials using NDVI imagery over the Sahel. Remote Sensing of Environment, 141, 79-89. http://dx.doi.org/10.1016/j.rse.2013.10.019
Examples
data(ex.n)
## maybe str(ex.n) ; plot(ex.n) ...