Paul,
You might well be right but I mention it as a possible reason. We have a big block of lidar date from a commercial company and the files were supplied as asc text with an asc extension. When you add them (add xyz) they appear as a black block until you zoom in to the point where you can see the individual points. It all depends on how much processing has been done by the suppliers - I prefer to do my own so ours came raw.
Tim
Tim Grubb
Archaeologist
Heritage Team
Gloucestershire County Council
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________________________________________
From: Issues related to Historic Environment Records <[log in to unmask]> on behalf of Paul Cripps <[log in to unmask]>
Sent: 06 July 2016 22:28:23
To: [log in to unmask]
Subject: Re: LIDAR Advice
Hi Rachel,
Tim's suggestion is unlikely. The suffix .asc denotes a specific GIS raster file format (ASCII Raster) comprising a descriptive header block then a bunch of cell values. As commonly used by suppliers like the Environment Agency. What Tim describes, ie point clouds in ASCII text format, would typically have a .xyz or .xyzi extension. Unless someone has just given a point cloud a .asc extension but as something is displaying, presumably in the right part of the world, Nick is most likely correct with the symbology being somewhat awry. You can check the data by looking at the Layer Properties or the values shown in the Legend; see if the min & max values make sense. If not, tweak the symbology as Nick suggests.
Re visualisation, do check out RVT which accepts a range of formats including .asc and outputs all manner of neat views of such data, way more informative than a simple one-direction hillshade or a coloured DTM (the Light Fantastic publication describes limitations of such views and some of the advanced ones RVT can do). Handily, for folk working in locked down IT environments, it comes packaged as a .exe Virtual Machine so no need to install anything, just run it and enjoy. The outputs can then be used in any GIS.
The download is here
http://iaps.zrc-sazu.si/en/rvt#v
The manual is here:
https://www.researchgate.net/publication/266632921_Relief_Visualization_Toolbox_version_11_Manual
Rebecca Bennett also prepared a very nice step by step guide for using RVT with QGIS:
http://www.pushingthesensors.com/wp-content/uploads/2015/01/APS_Workshop_4_lidar_RVT_LIVT.pdf
Both Rebecca and I run training sessions too if anyone wants to learn more.
More generally, if anyone needs help with anything further regarding effective use of Lidar, GIS or any other spatial analysis, may I suggest posting to the Antiquist list where there are numerous Lidar specialists willing to help.
All best,
Paul.
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