BlomURBEX extended - obtaining supporting absolute values from LiDAR
LiDAR data is available in a number of formats ranging from grid formats to comma seperated easting/northing/height values. This data can be handled by many CAD and GIS packages but these are not always the most efficient tools for handling or querying this often large type of dataset.
To assist in the management of LiDAR data we would recommend Global Mapper software. This solution provides a means to both import and extract absolute level information (O/S Datum) quickly and easily; as shown in the following examples generated with 50cm interval Blom Aerofilms LiDAR.
Opening LiDAR in Global Mapper:
Simply dragging the file on to the open application will import the data (users will need to confirm the co-ordinates system and datum (British Grid and OSGB36 most commonly for Great Britain)) and the height data is imported and rendered to indicate height through colour profile and hill shading.
As the cursor is moved around the screen position and level values are displayed instantly providing an initial means of picking specific values.
Perhaps a more accurate way of achieving this is to use the section tool. A section can be defined at any length and of numerous segments, so for instance, a curved road centreline could be followed continuously.
The section profile is displayed on screen giving start and end co-ordinates with levels. It is useful for seeing both high and low points or getting an average value for flat areas. The smaller the difference in height across the section, the more the vertical axis may be expanded meaning visual determination of values may be made more accuracately and with greater confidence. In this manner it is easy to find specific heights of or on structures. For example, pulling a section across the centre of roof will obtain a value for the ridge height. Similarly, short sections are useful for obtaining heights of walls and parapets at specific locations. The example below shows a section across a flat roof with both the height axis locked and unlocked (the lower section):
The example above shows that over a generally flat roof, the LiDAR provides a reasonbly consistent indication of height with just 5cm of variation from the mean value in over 50 metres.
Sections may cross large differences of height or encompass many variations in a small area. In these instances it may be difficult to identify precise values because of the range displayed as for example in the view below.
In order to more precisely work with the section, the information can be exported easily as XYZ comma delimited files. As they are geo-referenced they can be imported directly into the GIS or CAD base mapping model.
>>Next step - Extracting sections for CAD