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I try to use four LIDAR tiles in .asc with arcgis9.3. All of this tiles are centimeter round (in z) but one of them seems to be round to meter (see tile on the left up corner on the image below), while opening it with notepad we can see that it is centimeter round.

I compared the header of that four files and i didn't find any difference.

On that dropbox link you can find two LIDAR tiles. One is correctly read by arcgis when the second is not.

https://www.dropbox.com/sh/1pwuqr0nppb42qu/AAAk0zeVHbpVO1j9KZKMBf7Ca?dl=0

enter image description here

PolyGeo
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Panvjim0
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2 Answers2

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I think that the error isn't with the data so much as with the symbology of the first tile. That is, it has to be in the way that the tile is being rendered with a colour ramp. The reason I say this is that I downloaded the data you linked to and displayed the tiles in a different software package and this is what I got:

enter image description here

You'll notice that the 'Error' tile doesn't have the stepped appearance you have in your image (with no modification to the data, just a more appropriate colour ramp). I then changed the display minimum and maximum values and you can see that the tiles are seamless:

enter image description here

If the tiles were in different z units, you wouldn't be able to create the seamless display without first performing a unit conversion. So the good news is that there is nothing wrong with the data; it's just being rendered differently for the first tile than it is for the others in ArcGIS. Check out the display properties (stretched symbology) of that tile compared with the others.

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WhiteboxDev
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Actually the problem is not really coming from the display properties. In fact, even changing the streched symbology I still have the same error. The error come from the reading of the data by arcgis. When opening a .asc with notepad, we can see that a default value is set for nodata. In my case the default value was : -9999 (see first picture below). I changed this value by -9999.0 and then it works (ie arcgis read correctly the data)(see second picture below).

Note that some files where the nodata value is -9999 (and not -9999.0) are correctly reading by ArcGIS which is quite strange !

enter image description here

enter image description here

Panvjim0
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    I suspect that the reason why the symbology was messed up was because of the wide range of apparent values in the tile, having not read the NoData value properly during import. Also, the NoData value was the same for each of the two tiles you uploaded. Anyhow, I'm glad you tracked down the issue. – WhiteboxDev Oct 21 '14 at 12:54