Changes between Version 20 and Version 21 of Processing/laguserguide


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Timestamp:
Jun 29, 2012, 10:50:59 AM (12 years ago)
Author:
jaho
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  • Processing/laguserguide

    v20 v21  
    11= LAG User Guide =
    22
    3 The following guide provides an overview of LAG features and offers some hints on how to utilize them for the best processing efficiency. Some of these are just convenient methods of doing things while other can offer a significant performance improvement. Most of the values discussed below have been set up for optimal performance by default, however different data sets and tasks can benefit from different configurations.
     3The following guide provides an overview of LAG features and offers some tips on how to utilize them for the best processing efficiency. Some of these are just convenient methods of doing things while other can offer a significant performance improvement. Most of the values discussed below have been set up for optimal performance by default, however different data sets and tasks can benefit from different configurations.
    44
    55== System Configuration ==
    … …  
    99== Opening Files ==
    1010
    11 [[Image(fileopener.png,align=center)]]
    12 {{{
    13 #!div style="font-size: 80%; text-align: center"
    14 File opener dialog.
    15 }}}
    16 
    1711There are following options on the file opener dialog:
    1812* **Point Skip Number**
    … …  
    2014* **Fence**
    2115    Using the fence allows loading selected part of the flighline(s) into LAG. If there's only a small area in the data that you need to see in full detail, it is a good idea to load the whole data using point skipping, then select the area of interest with the fence in the overview window and click refresh on the file opener dialog after checking the //Use Fence// button.
     16* **Ascii files**
     17    To load ascii files you need to provide parse string that gives the order and number of columns in the ascii file and scale factors for x, y and z. The default laslib scale factors for text files are 0.01. Default scale factors we used to use are 0.001, which are also default LAG values.
     18* **Advanced**
     19    //Advanced// button opens Advanced Load Dialog which allows to set additional options like filters and Quadtree Settings.
     20
     21[[Image(Screenshot-Advanced load options.png,align=center)]]
     22{{{
     23#!div style="font-size: 80%; text-align: center"
     24Advanced Load Dialog.
     25}}}
     26
     27* **Filters**
     28    Filters allow fine-tuning the loading of files to only use points that meet given criteria. They are quite self-explanatory. For text fields in //Return// and //Classification// filters a space separated list of values should be used. The buttons next to the filters can be used to specify whether a selected range of values should be kept or dropped.
    2229* **Resolution Base and Resolution Depth**
    2330    These two values control the construction of the quadtree and directly affect both loading times and rendering speed of the data. Each leaf (point bucket) in the quadtree can have a number of sub-buckets which store points to display at different zoom levels. For example when viewing a whole flightline in the overview window there is no need to render every single point or store all the points in memory at once. Thus sub-buckets containing every n-th point are used instead. \\
    … …  
    2734* **Points to hold in cache**
    2835    This determines the maximum number of points to hold in memory at any given time. Once this number is exceeded the points will be written to the hard drive which is much slower then RAM. This only concerns the quadtree and LAG is generally going to need some more that the specified amount. This value should be set roughly to 25% of your total available memory. Setting it too high will result in system memory swapping and setting it too low will result in quadtree uncaching data to hard drive more often. Note that points stored in memory are bigger in size then those stored in the LAS files by roughly 40%, so loading a 1GB file requires 1.4GB buffer.
    29 * **Ascii files**
    30     To load ascii files you need to provide parse string that gives the order and number of columns in the ascii file and scale factors for x, y and z. The default laslib scale factors for text files are 0.01. Default scale factors we used to use are 0.001, which are also default LAG values.
     36
    3137
    3238== Panning ==
    … …  
    6268LAG currently supports UTM and latlong (or longlat: x = longitude, y = latitude) projections. By default files in both formats will be displayed using UTM coordinates. You can change it by going to //Tools >> Use latlong coordinates//.
    6369
    64 Latlong is generally a preferred projection because it doesn't require additional zone information. Latlong files can be saved as both latlong and UTM, while UTM files should not be converted, unless they contain projection information in the header's VLR geo keys. Alspp produced UTM files don't contain this information (they do but under wrong GeoKeys...) so this conversion should be avoided for the time being. Also latlong files seem to have higher precision than UTM files (up to around 10th of a milimeter), which is probably an overkill for the actual lidar precision. By default this values are rounded to precision of 1 centimeter when converting latlong to UTM. To prevent precision loss you can select // Use full precision // option on file saver dialog, however this will result in bigger files and possibly storing some scanner noise.
     70Latlong is generally a preferred projection because it doesn't require additional zone information. Latlong files can be saved as both latlong and UTM, while UTM files should not be converted, unless they contain projection information in the header's VLR geo keys. Alspp produced UTM files don't contain this information (they do but under wrong GeoKeys...) so this conversion should be avoided for the time being. Also latlong files seem to have higher precision than UTM files (up to around 10th of a milimeter), which is probably an overkill for the actual lidar precision. By default this values are rounded to precision of 1 centimeter when converting latlong to UTM.
    6571
    6672== Other Options ==