[R-sig-Geo] read function for LAS data

[Michael Sumner]

Thanks Etienne.

On Tue, Jun 8, 2010 at 12:31 AM, Etienne Bellemare Racine
<etiennebr at gmail.com> wrote:
> Michael,
>
> I have not gone through extensive testing, but it seems pretty fast and
> usefull for my 1.0 las. I've loaded a 235 Mb file on a USB drive, and it ran
> in ~20 seconds. SAGA, in comparison did it in 3 min 22 seconds.
>
> Cheers,
> Etienne
>
> Le 2010-06-06 10:18, Michael Sumner a écrit :
>
> Hello,
>
>
> To other issue I see here is that R is loading the whole file in memory, so
> if you can manage small files, that might not be that easy with (standard)
> larger ones. Don't you think ?
>
>
> That was certainly true of the version of code I posted, but writing a
> more flexible version is not difficult, and actually less difficult
> than I expected. I've implemented arguments to "skip" and read "nrows"
> at a time, so there is the beginnings of a wrapper around the core
> read for building more flexibility.
> (I was thinking of including subsetting of various kinds which really
> makes it more complicated, and the appropriate level to handle that is
> in a wrapper to this function).
> I've updated the R source on my site, and here's a new example. This
> should be considered as a rough working draft, the details can be
> hidden in the final suite of functions. My chunk/rows handling is
> pretty awkward, and may have bugs for particular record numbers.
> Any testing you can provide would be greatly appreciated.
> # new version with "skip" and "nrows" arguments
> source("http://staff.acecrc.org.au/~mdsumner/las/readLAS.R")
> f <- "lfile.las"
> ## get just the header
> hd <- readLAS(f, returnHeaderOnly = TRUE)
> numrows <- hd$`Number of point records`
> ## [1] 1922632
> ## read in chunks, and pass to DB or ff, or subset by sampling, etc..
> rowskip <- 0
> chunk <- 1e5
> rowsleft <- numrows
> system.time({
> ## keep track of how many rows we skip, and how many are left
> for (i in 1:ceiling(numrows / chunk)) {
> 	if (rowsleft < chunk) chunk <- rowsleft
> 	if (chunk < 1) break;
> 	d <- readLAS(f, skip = rowskip, nrows = chunk)
> 	rowskip <- rowskip + nn
> 	rowsleft <- numrows - nn
> }
> })
> #   user  system elapsed
> #   1.10    0.55    1.64
> On Sun, Jun 6, 2010 at 8:09 PM, Etienne Bellemare Racine
> <etiennebr at gmail.com> wrote:
>
>
> This is interesting, I'll try your code on my lidar files in the next few
> days.
>  2010-06-04 22:36, Michael Sumner wrote :
>
>
> Thanks Alex, I will eventually post this to a broader audience.
> I've used liblas and lastools, but the aim here is for a pure R
> implementation that is built directly from the LAS specification
> without 3rd party tools.
>
>
> What might be of interest in using liblas is that it provides support for
> many las versions and they plan to provide support for some versions to come
> (conditional to funding) so having an R binding might be of interest here.
> They are also working on the integration of a spatial index which would
> allow easier handling of large files. I must say I don't know how hard
> writing a wrapper for R might be for that particular tool.
> To other issue I see here is that R is loading the whole file in memory, so
> if you can manage small files, that might not be that easy with (standard)
> larger ones. Don't you think ? Did you give a try to the R SAGA package.
> There is a module for loading las files but again, I don't know how it
> manages memory. I guess that it could be possible to use some sort of ff
> package to handle bigger files, but that's just on the top of my head.
> Etienne
>
>
> The R code already works quite well to extract x/y/z/time/intensity,
> it just needs some extra work to tidy up and generalize things and
> ensure that very big datasets can be read.
> Cheers, Mike.
> On Sat, Jun 5, 2010 at 6:07 AM, Alex Mandel<tech_dev at wildintellect.com>
>  wrote:
>
>
> On 06/03/2010 07:54 PM, Michael Sumner wrote:
>
>
> Hello,
> I'm looking for interest in this functionality and eventually working
> it into a package.
> I don't actually use LAS data much, and only have one example file so
> I'm hoping others who do or know others who would be interested can
> help. I have previously posted this to r-spatial-devel.
>
>
> I think there are people who would use it. You might want to have a look
> at http://liblas.org/ (some of the same people that do gdal/org work)
> Wrapping this library might be a good approach. There are example files
> available too.
> Thanks,
> Alex
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