Subject: Marine Geospatial Ecology Tools (MGET) help
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| From: | "Jason Roberts" <> |
|---|---|
| To: | "'Sherilyn Tan'" <> |
| Cc: | <> |
| Subject: | RE: [mget-help] Help required for |
| Date: | Mon, 14 Oct 2013 11:09:55 -0400 |
Hi Sherilyn, Ah. It sounds to me like you wanted to use ArcGIS linear referencing to deal with a problem of not having x and y coordinates (e.g. lat and lon from a GPS) of each coral observation. Instead of x and y, you had either the time and/or distance swam since the starting point of the transect, and you wanted to use that elapsed time or distance to locate the points along the transect. Is that correct? If the answer is yes, then I believe you can use the Make Route Event Layer tool to create a point feature layer from the route and route events. This will do the job of computing x and y coordinates for each observation, and representing it as a “point” in ArcGIS’s data model, instead of a “route event” which is a slightly different concept in that data model. You should then be able to use that layer as the “points” I mentioned in my first response. If that does not work for some reason, try saving that layer to a feature class or shapefile, and then using it. If the answer is no, then could you please tell me what the columns are in your original coral observations table, before you used it to create route events? Best, Jason From: Sherilyn Tan [mailto:]
From: Hi Sherilyn, Thanks for your interest in MGET. The Calculate Species Diversity Index for Polygons tool is designed for the scenario where you have a bunch of points scattered across a region and you want to divide the region into study sites defined by polygons or a grid defined by cells and a calculate diversity index value for each site or grid cell. Each point represents an observation of a species, optionally with a count of the number of individuals observed (the count is only required for certain diversity indices). It sounds like you have line transect survey data for several study sites, in which a diver or ROV swam the transects at each site and recorded locations and species of coral. If those sightings are in the form of points, then you can calculate diversity for each site by creating a polygon layer that has a polygon surrounding each site. If you do not have a polygon layer, I suggest you try the Minimum Bounding Geometry tool that comes with ArcGIS (under Data Management à Features). This tool allows you to create bounding rectangles or convex hulls that enclose your features of interest (i.e., the coral points). If the coral points have a field that defines the study site, you can use the Group Option and Group Fields to tell the tool to create one polygon enclosing the points for each site. That is what you will need for the MGET Diversity tool. Once you have that polygon layer, add a field to it to receive the diversity index value (use a FLOAT or DOUBLE data type). Then use the MGET tool. Give it the points and the polygon layer. You’ll have to tell it which field of the points holds the species ID, and which field of the polygons should receive the diversity index value. Pick the diversity index (see Wikipedia for some descriptions). If for some reason you do not have points, you only have polylines, you will have to convert them to points. There are easy tools for doing that, but before I recommended anything, I’d want to know what the fields were of the polylines. It is standard to store transect effort lines as polylines but not standard to store species observations as polylines, unless the lines represent a summary for the transect (e.g. counts of species observed along the entire transect), or it is not possible to be precise about the location of an observation, in which case an observation might be stored as a line segment rather than a point. Best regards, Jason From: Sherilyn Tan Hi, I am trying to Calculate Species Diversity Index for my data on corals. However it is in the form of polylines (points on transact lines) rather than polygons. As such, i am lost as to how to continue to use your tool for "Calculate Species Diversity Index for Polygons." Each site has a few transacts (polylines), and I need to calculate the species diversity index for each site and also compare against other various sites. How do I go about doing this? For your advise please. Thank you. Regards Sherilyn |