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I have downloaded LiDAR information as a .asc file and a .tif file, and even though I have tried multiple methods to convert them to a dem I am having no luck. Grass GIS says there is an invalid northpoint on the ascii data. Could someone here point me in the right direction?

Here are the two datasets: 1 and 2.

  • Thank you. I tried converting to grass ASCII, but that was not working. I've resigned and installed arcGIS and am now trying to figure out how to use it. Thanks – Yaro Nov 1 '14 at 8:10
  • See my reply to your other recent question. I imported your ASCII file in its original format into the GIS Whitebox GAT (which I develop) with absolutely no problems. There is nothing wrong with your file. – WhiteboxDev Nov 1 '14 at 14:54
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Given your error, my guess is that when you are importing the file to GRASS, it is expecting a GRASS ASCII raster format, which has a header that looks like this:

north: ####.###

south: ####.###

east: ####.###

west: ####.###

rows: ####.###

cols: ####.###

Instead of an ArcGIS ASCII grid, which has a header that looks like this:

NCOLS ###

NROWS ###

XLLCORNER / XLLCENTER ###

YLLCORNER / YLLCENTER ###

CELLSIZE ###

NODATA_VALUE ###

You have the later format. Notice that the ArcGIS ASCII format doesn't explicitly contain a 'North' entry, which the GRASS format import tool is looking for. So you can either change the header part of your file and import it as a GRASS file or select an import option that explicitly handles an ArcGIS ASCII grid. If you should choose to alter the ArcGIS ASCII format to a GRASS ASCII raster you can calculate the north, south, east, and west values as follows:

north = YLLCORNER + NROWS * CELLSIZE

south = YLLCORNER

east = XLLCORNER + NCOLS * CELLSIZE

west = XLLCORNER

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