[R-sig-Geo] write/readOGR issue with date / time strings

[MacQueen, Don]

You don't truly have a date/time field, even though it looks like it. You
have a factor. 

So the first thing I would try is to convert the date/time field from
factor to character using format() or as.character() before writing the
shapefile. (That is, do the conversion myself rather than relying on
writeOGR's internal conversion; see the help page for writeOGR).

I'm a little bothered by the fact that Lat and Lon are factors; they
shouldn't be. This suggests that somewhere in your data is at least one
row where lat or long is not a valid number. But writeOGR doesn't use
these particular Lat and Lon columns to write coordinates to the
shapefile, so maybe it doesn't matter.

-Don

-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 11/11/11 12:54 PM, "Corrie Curtice" <corrie.curtice at duke.edu> wrote:

>Hello, 
>
>Apologies if this has already been addressed somewhere, I did a brief
>search
>of archives but didn't find quite this issue.
>
>I'm writing out an ESRI shapefile.  My spdf has a date/time field.  Looks
>like this:
>
>> head(spdfUTM at data)
>           krillGMTtime          Lat          Lon
>1   2010-05-12 12:34:21 -64.67655969 -62.15040195
>21  2010-05-12 12:35:12  -64.6771229  -62.1519511
>38  2010-05-12 12:36:02 -64.67775863 -62.15340614
>57  2010-05-12 12:36:53 -64.67838269 -62.15494829
>78  2010-05-12 12:37:43 -64.67901497 -62.15647203
>100 2010-05-12 12:38:37 -64.67973667 -62.15773224
> 
>All three fields are reported to be "factors" by str.  writeOGR appears
>happy:
>
>> writeOGR(spdfUTM,dd,layer="krillPoints-UTM",driver="ESRI
>Shapefile",verbose=TRUE,overwrite=TRUE)
>$object_type
>[1] "SpatialPointsDataFrame"
>$output_dsn
>[1] "/users/corriecurtice/documents/Data_2010/Shapefiles/"
>$output_layer
>[1] "krillPoints-UTM"
>$output_diver
>[1] "ESRI Shapefile"
>$output_n
>[1] 11179
>$output_nfields
>[1] 3
>$output_fields
>[1] "krillGMTtime" "Lat"          "Lon"
>$output_fclasses
>[1] 4 4 4
>$dataset_options
>NULL
>$layer_options
>NULL
>Warning message:
>In writeOGR(spdfUTM, dd, layer = "krillPoints-UTM", driver = "ESRI
>Shapefile",  :
>  existing layer removed
>
>When I read it right back in again, the date/time field is NAs.  This is
>also true if I load the shapefile into ArcMap.
>
>> foo <- readOGR(dd,layer="krillPoints-UTM",verbose=TRUE)
>OGR data source with driver: ESRI Shapefile
>Source: "/users/corriecurtice/documents/Data_2010/Shapefiles/", layer:
>"krillPoints-UTM"
>with 11179 features and 3 fields
>Feature type: wkbPoint with 2 dimensions
>
>> head(foo at data)
>  krillGMTti          Lat          Lon
>1       <NA> -64.67655969 -62.15040195
>2       <NA>  -64.6771229  -62.1519511
>3       <NA> -64.67775863 -62.15340614
>4       <NA> -64.67838269 -62.15494829
>5       <NA> -64.67901497 -62.15647203
>6       <NA> -64.67973667 -62.15773224
>
>Thoughts? Am I missing something obvious?
>
>I can break it up into separate date and time fields, but since the field
>is
>simply a factor anyways I'm not sure how that would help.
>
>Cheers,
>
>Corrie
>
>---
>Corrie Curtice
>Research Analyst
>Marine Geospatial Ecology Lab
>Nicholas School of the Environment, Duke University
>http://mgel.env.duke.edu
>em: corrie.curtice at duke.edu
>ph: 252-504-7538
>
>
>
>
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>
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