Raster to ASCII, gets cut off

[ValerieSahakian]

Hi,

I am trying to export a tif of some aerial lidar data I have to an ascii.  I would like to do this so I can then convert the ascii to a .grd file, and plot it with GMT. 

The only problem is that when I export to an ascii from arc using the Raster to ASCII tool, it consistently says in the header that there are for example 25500 rows, but when I do a line count on it in unix there are fewer (say, 19456 for example).  To be able to convert it to a .grd file, I need to change the number of rows in the header, but then when I plot it up, the southern part is chopped by about .05 to .1 degrees of latitude.  I have tried playing with all the Environment variables, but to no avail - there are always fewer columns than the header indicates, and the data is chopped.

Has anyone else every experienced this, and know of a solution?

Thanks!

[larryzhang]

With tools in ArcGIS or others for ascii export from very larger LAS file, please use the following approach:

1. A very large LIDAR data (LAS) should be sub-zoned (tiled) into smaller tiles of LIDAR (with certain overlaps) first; and then

2. export those smaller LiDAR data into ascii

However, for your TIFF of an image (orginally, LIDAR) to ascii, it might be challenging to do 'properly'. The reason is: your TIFF data could be already resampled from point clouds into continuous cells. Generally speaking, most tools like 'raster to ascii' work fine, only when your raster is 'categorical, or discontinuous data'.

Of course, the ArcGIS Help shows that it works for all valid rasters. So, if you want the tool working for your raster TIFF, it may be highly required to tile, before export...