topic Re: LIDAR asc files without spatial references processing ArcGIS 10.0 in Spatial Statistics Questions

LIDAR asc files without spatial references processing ArcGIS 10.0

JosselineLou — Sat, 28 Sep 2013 11:16:26 GMT

Hello, I recently acquired LIDAR files which are in .asc format. My objective is to create an automatic model using modelbuilder so any LIDAR files of a watershed area can be processed in order to extract paramters such as geographical extend...
But I'm stuck at the first step, I have the raw LIDAR data in .asc format and when I open it in notepad++, it shows only 3 columns and about 3 millions rows of datas, the matter is that I have no spatial reference, I don't have any information such as :
NCOLS xxx
    NROWS xxx
    XLLCORNER xxx
    YLLCORNER xxx
    CELLSIZE xxx
    NODATA_VALUE xxx

I can specify myself the number of rows, columns and the nodata value but I can't specify the cellsize or the geographical extend of the dataset. I can't create a Raster using the ASCII to Raster Tool (which is strange by the way considering a raster doesn't need spatial references to exist). I'd like to know how I could convert such files into Raster data (preferably TIFF) which I can then specify spatial references.
Thanks in advance,
Josseline

Re: LIDAR asc files without spatial references processing ArcGIS 10.0

XanderBakker — Mon, 30 Sep 2013 06:18:34 GMT

Hello, I recently acquired LIDAR files which are in .asc format. My objective is to create an automatic model using modelbuilder so any LIDAR files of a watershed area can be processed in order to extract paramters such as geographical extend...
But I'm stuck at the first step, I have the raw LIDAR data in .asc format and when I open it in notepad++, it shows only 3 columns and about 3 millions rows of datas, the matter is that I have no spatial reference, I don't have any information such as :
NCOLS xxx
    NROWS xxx
    XLLCORNER xxx
    YLLCORNER xxx
    CELLSIZE xxx
    NODATA_VALUE xxx

I can specify myself the number of rows, columns and the nodata value but I can't specify the cellsize or the geographical extend of the dataset. I can't create a Raster using the ASCII to Raster Tool (which is strange by the way considering a raster doesn't need spatial references to exist). I'd like to know how I could convert such files into Raster data (preferably TIFF) which I can then specify spatial references.
Thanks in advance,
Josseline

Hi Josseline,

The data you received is an XYZ ASCII point cloud (vector) which is quite different from the raster format you're trying to obtain. Please read these help topics for more information on both formats.

Esri ASCII raster format
and
What is lidar data?

LiDAR data is normally a lot richer than XYZ only. In your case it has been stripped down to XYZ. ArcGIS has several ways of working with LiDAR data, but those are normally based on LAS files which are imported to a LAS dataset:
What is a LAS dataset?

At this moment Esri still does not provide a simple straightforward way of converting XYZ (ASCII) files to LAS. If you also feel that this is a necessary tool you can support the idea here (it's under consideration):
Ability to convert xyz point data to LAS format

In the mean time there are several other ways of doing this. I found a tool on the ArcScripts site (although I have no idea what version of ArcGIS it supports):
ArcScripts: Convert XYZ,ASCII Raster files to ESRI GRID-Batch

Another possibility is using the ASCII 3D To Feature Class (requires 3D Analyst) which results in a PointZ featureclass followed by a Point to raster. You can read more about this in this Esri Blog: Lidar Solutions in ArcGIS_part2: Creating raster DEMs and DSMs from large lidar point collections.

A very powerful toolset is LAStools:
http://www.cs.unc.edu/~isenburg/lastools/
and
http://rapidlasso.com/lastools/

Please bear in mind that LAStools is not free for commercial applications:
http://rapidlasso.com/pricing/

Some more reading on Creating raster DEMs and DSMs from large lidar point collections

Kind regards,

Xander

Re: LIDAR asc files without spatial references processing ArcGIS 10.0

JosselineLou — Tue, 01 Oct 2013 09:29:37 GMT

Thank you very much for your quick answer, it helped me very much. I finally used the ASCII 3D To Feature Class, I had a problem for getting the attribute table showing the elevation values in order to create an interpolated raster afterwards. But I resolved it by myself, thanks again for the post, I know now more about the data I'm dealing with !
I think I'm will use ERDAS to geolocalize the raster I will create (I have some aerial photography)
Thank you again (for the third time I think).

Take care,
Josseline

Re: LIDAR asc files without spatial references processing ArcGIS 10.0

XanderBakker — Tue, 01 Oct 2013 12:00:04 GMT

Hi Josseline,

I'm glad I could be of any assistance. If you think it was helpful you can use the "check mark" and "arrow" buttons in order to help other members find useful information:

[ATTACH=CONFIG]27931[/ATTACH]

More info here: http://resources.arcgis.com/en/help/forums-mvp/

Kind regards,

Xander