error in readShapePoly

Thanks Roger!

Are there any instances in which one would want delete_null_obj=FALSE?

-----Original Message-----
From: Roger Bivand [mailto:Roger.Bivand at nhh.no]
Sent: Wednesday, June 10, 2009 10:36 AM
To: Hurlbert, Allen H. (Biology)
Subject: RE: [R-sig-Geo] error in readShapePoly

On Wed, 10 Jun 2009, Hurlbert, Allen H. (Biology) wrote:

Hi Roger,

Here is the result of the traceback():

4: .shp2srsI(shapes[[belongs[[i]][j]]],
.nParts.shpI(shapes[[belongs[[i]][j]]]),
      force_ring = force_ring)
3: .asSpatialPolygonsShapes(Map$Shapes, IDs, proj4string =

proj4string,

      force_ring = force_ring)
2: .Map2PolyDF(Map, IDs = IDvar, proj4string = proj4string, force_ring

=

force_ring,
      delete_null_obj = delete_null_obj, retrieve_ABS_null =
retrieve_ABS_null)
1:

readShapePoly(paste("\\\\Bioark.bio.unc.edu\\hurlbertallen\\GIS\\BirdRan

geMaps\\NatureServe3.0\\",
      as.character(families[f]), "\\", as.character(spp.list[s2,
          1]), sep = ""), proj4string = CRS("+proj=latlong
+datum=NAD83"))

The shapefiles are bird range maps available online from NatureServe
here: http://www.natureserve.org/getData/birdMaps.jsp. The problem

file

is trin_inca_pl.shp which is included in the zipped 'Scolopacidae'

file

on that page.

Unfortunately, I am unfamiliar with the syntax of readOGR() and can't
quite figure out how I'm supposed to use it to read in a shapefile.

It is a bit more revealing:

trin_inca_pl <- readOGR("Scolopacidae", "trin_inca_pl")

Error in ogrInfo(dsn = dsn, layer = layer, input_field_name_encoding =
input_field_name_encoding) :
  NULL geometry found

and suggests using the fix in:

trin_inca_pl <- readShapePoly("Scolopacidae/trin_inca_pl.shp",

+  delete_null_obj=TRUE)
Warning message:
In .Map2PolyDF(Map, IDs = IDvar, proj4string = proj4string, force_ring =

force_ring,  :
  Null objects with the following indices deleted: 134

So the data provider has inserted a NULL geometry into the data - they
shouldn't do it, but it has been seen before. Could you summarise to the

list, please? I'll see if I can add a test in readShapePoly to point
users
to the optional argument.

Roger

Thanks!
Allen

-----Original Message-----
From: Roger Bivand [mailto:Roger.Bivand at nhh.no]
Sent: Wednesday, June 10, 2009 9:38 AM
To: Hurlbert, Allen H. (Biology)
Cc: r-sig-geo at stat.math.ethz.ch
Subject: Re: [R-sig-Geo] error in readShapePoly

On Wed, 10 Jun 2009, Hurlbert, Allen H. (Biology) wrote:

Hello list,



I'm new to GIS in R, so I appreciate any pointers with my problem.



I have code that uses readShapePoly to read in shapefiles in a loop

and

does some basic operations. This code appeared to be working great

for

twenty or so files, but then on one shapefile bonked with the

following

error:   Error in from[j]:to[j] : NA/NaN argument.



The problem shapefile opens fine in ArcGIS and there is nothing

readily

different about its attribute table or source information that I can

see

(and furthermore, all shapefiles are from the same standardized

source,

although of course that doesn't mean one of them didn't get messed up
somewhere along the way). I am running 2.7.2 on Windows XP x64.

Could you 1) try readOGR() in rgdal instead of readShapePoly() in
maptools
if possible, and see if the problem is repeated; 2) post either the
output
of traceback() run immediately after the error occurs (will show

where,

more or less, the problem is in code) here and/or the shapefile(s) all
3-4
files in a zip archive on a website and post the URL here so that

others

can debug this? The problem seems to be a shot Pstart vector putting

an

invalid value into the range from which to extract ring coordinates,

but

the question is why it is shot.

If you can say something about the origin of the file, this may also
help
(what software wrote it), some have broken *.shx files.

Roger

Thanks in advance,

Allen


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