Summarizing point data to multi point data and creating convex hull in R

Question

I have latitude and longitude information like 26.847905 73.9575005 for about 800 points, I need to trim these lat/lon information to say 3 decimal places.

I used the following syntax in R

# Rounding off Coordinates of each of point to 3 decimal places
shp1_DE$lon <- round(shp1_DE$coords.x1, 3)
shp1_DE$lat <- round(shp1_DE$coords.x2, 3)

Now I have many points with lat/lon for example 26.847, 73.957 etc...

I want to summarize data to these points and form point-multipoint shapefile.

After that I need to create convex hull for each of these features. How to go about it in R?

Answer 1

To create a convex hull you can use function chull from grDevices.

NB: This function returns the indices of the points in the input, not the points itself. Furthermore I was using it to draw lines, so I had to add the first point again as last point. The code I used looks like this:

hull <- chull(topo)
hull <- c(hull, hpts[1])
hullpts <- topo[hull,c(1,2)]

Answer 2

It is quite unclear what you attempt to do. For instance summarize and feature are quite vague without further context. So I am guessing here.

With your rounding of the coordinates you in effect moved the points in "square" cells to a central point for each cell. You don't need to. Just imagine the cells, and loop over them, calculating the aggregate you need (count/sum/avg(?)) for the points in each cell.

Every grid-cell could then serve as the complex hull for the points inside it. Use rect() and text() to draw the results into a plot.