LoCoH: FAQsLoCoH: FAQsFor technical help using the scripts and applications on this page, email Scott Fortmann-Roe at scottfr@gmail.com. For scientific help and queries about the LoCoH algorithm and its uses, direct your emails to Wayne Getz at getz@nature.berkeley.edu.
What does LoCoH stand for?LoCoH stands for LOcal COnvex Hull. The name comes from the .building blocks. of the method, namely the little minimum convex polygons that are constructed around each point and then merged together to create isopleths.
When should I use LoCoH?The main advantage LoCoH is that it respects hard edges in an animal's movement patterns, such as lake shores, ravines, or roads. LoCoH would be a reasonable method for analyzing the movements of any animal with these characteristics. However, LoCoH requires a good number of observations in order to model the edges in the habitat. Thus it will work best when there are a lot of data available, such as regular sampling from a GPS or radio collar.
What's the difference between k-NNCH and Fixed k LoCoH?Nothing, they are the same name for different things. k-NNCH, however, is a bad name so please use Fixed k LoCoH when referring to the algorithm.
How many versions of LoCoH are there?There are currently three LoCoH products:
| Information of ArcObjects LoCoH for ArcGIS 9.x and 9.x |  |
R is an open source statistical programming language. It is similar to S-Plus, but open source and free. There are a lot of websites with R tutorials and R libraries (additional functions you can use within R), including several which are specifically designed for analyzing animal movements.
What is adehabitat?Adehabitat is a library for R. Once installed, a number of additional functions, including LoCoH, are available for analyzing animal movements within the R environment. For more information, see the AniMov website.
| Go to the AniMov Website | |
The number of points depends on the amount of memory of the machine. The R-version of LoCoH was able to analyze 4000 points in 4 hours on a PC with a 3 GHz processor and 1 Gb of RAM. The web version of LoCoH is limited to approximately 1,000 points.
Are there any known bugs?R has a problem plotting and exporting polygons with holes. A work-around has been developed by creating 'bridges' between the outer edges of the isopleth and any holes. This operation will not change the area or shapes of isopleths, but will change their perimeters.
I have a lot of point data in one file that I want to analyze in parts (e.g., dry season vs. wet season). Can I do this with LoCoH?You have two options here. You can either subset your data into separate files, and then run them through LoCoH individually. Or you can use R statements to select subsets of the entire dataset using the R command line (see R tutorial)
How are isopleths capped?Isopleths are constructed by merging local hulls (sorted smallest to largest) until they enclose n% of the original points. However it is rare that exactly n% of the points are enclosed. The R version of LoCoH takes the largest union of hulls that encloses <= n%. Thus for example the 50% isopleth for a dataset of 600 points would enclose 300 points or a bit less. The ArcView 3.x version of LoCoH has options to cap isopleths using either <= or >= n% of points.
What do I do after constructing isopleths?There are a number of ecological questions one can begin to address with utilization distributions. For example: Where do animals spend most of their time (and why)? What is the optimal design of a reserve? Which corridors are used to connect habitat patches? etc.
The R-script seems to run slow, is there any way of optimizing it?One of the main advantages of developing scripts in an open source language like R is expanding the pool of developers who can further develop the code. If you see a way the code can be optimized please let us know or contact the mantainer of Adehabitat.
Why do I have to select my '.shp', '.shx', and '.dbf' files; can't I just find one, and you automatically upload the other two?No. Javascript (which would need to be used to do this) has a number of built in constraints involving file uploading. In order to prevent hackers from secretly accessing files on your computer, Javascript prevents web sites from uploading files that have not been specifically specified by the user. Therefore you must select each one of the three files yourself.
What coordinate system should my data be in?LoCoH can process points in any coordinate system. If points are in a geographic coordinate system (latitude-longitude), they should be written as decimal degrees (dd.dddd). Some GPS units express coordinates as degree decimal-minutes (dd.mm.mmmm), which need to be converted. Note that the reported area of isopleths will not be meaningful if points are expressed in geographic coordinates, so it is recommended that you project your points into a planar projection system such as UTM.
