<div dir="ltr">If you specify a resolution of 50 to the EPT reader, the EPT reader will determine a minimal octree depth such that this depth provides a precision at *least* as precise as what you've specified. Because EPT is an octree structure with discrete precision steps, the returned precision will likely be more precise than your request. The nomenclature of the 'resolution' option was lifted from the GDAL writer (<a href="https://pdal.io/stages/writers.gdal.html#writers-gdal" target="_blank">https://pdal.io/stages/writers.gdal.html#writers-gdal</a>), where it represents a spacing value - so a smaller value means *more* precision.<div><br></div><div>That means that for your request of resolution=50, the EPT reader is selecting the minimum octree depth such that the octree cell width is less than 50 units.<div><br></div><div>So your query will capture at least one point for every 50x50x50 unit volume, if data exists in that volume. I wouldn't say that this is representative of that 50m^3 volume - only that you're guaranteed to have at least one point from this volume if one exists.</div><div><br></div><div>If you run your pipeline with `--debug` you can see logs of the actual resolution used for the query as well as the corresponding octree depth.</div></div><div><br></div><div>The resolution for each depth can be determined by the bounds (<a href="https://entwine.io/entwine-point-tile.html#bounds">https://entwine.io/entwine-point-tile.html#bounds</a>) and the span (<a href="https://entwine.io/entwine-point-tile.html#span">https://entwine.io/entwine-point-tile.html#span</a>). At every subsequent depth, the bounds are bisected into octants although the number of grid cells remains constant, effectively doubling the precision in each spatial dimension.</div><div><br></div><div>Hopefully this helps to clarify things.</div><div><br></div><div>- Connor<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Apr 1, 2019 at 7:51 AM Matt Beckley <<a href="mailto:beckley@unavco.org" target="_blank">beckley@unavco.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div dir="ltr">Hi - thanks for the responses. Basically, I'm trying to develop a workflow to calculate the number of points per class in a given ept dataset. My experience is that the `pdal info --stats` command will read all of the data into memory and will not work on large ept files (like the usgs lidar datasets). Conor helped me out and suggested that I could use the "resolution" flag to estimate the number of points at a given level in the ept structure, and I've done that with a resolution = 50. So, for example, I have run a query like:</div><div dir="ltr"><br></div><div dir="ltr">pdal info --stats --filters.stats.dimensions=Classification --filters.stats.count=Classification ept://<a href="https://s3-us-west-2.amazonaws.com/usgs-lidar-public/USGS_LPC_MD_VA_Sandy_NCR_2014_LAS_2015" target="_blank">https://s3-us-west-2.amazonaws.com/usgs-lidar-public/USGS_LPC_MD_VA_Sandy_NCR_2014_LAS_2015</a> --readers.ept.resolution=50 --readers.ept.threads=12</div><div dir="ltr"><br></div><div dir="ltr">I'm trying to understand if the counts I get per classification is representative of a 50 m^2 area? It seems like from the documentation (and Jim's answer), that it is trying to take data at the octree level that is closest to the specified resolution. So, is there a way I can "back out" the point totals per classification to get a representative count per classification for the entire dataset? Is there a way to calculate what the actual returned resolution level is? Currently I am just taking a ratio between total count of the entire dataset to returned count from the subset dataset using the "resolution" flag. I then apply that ratio to the different class counts to get a rough estimate of points per classification for the entire dataset. This is certainly not the best method as it will over-estimate some of the classification totals. </div><div dir="ltr"><br></div><div dir="ltr">Thanks for your help.</div><div dir="ltr"><br></div><div dir="ltr">matt.<br clear="all"><div><div dir="ltr" class="gmail-m_-5118659665164687995gmail-m_-5011325440620476816gmail-m_-7683089810198383044m_555617595015237444gmail_signature"><div dir="ltr"><div><div dir="ltr">---------------------------<div>Matthew Beckley</div><div>Data Engineer</div><div>UNAVCO/OpenTopography</div><div><a href="mailto:beckley@unavco.org" target="_blank">beckley@unavco.org</a></div>303-381-7487</div></div></div></div></div><br></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Mar 25, 2019 at 1:30 PM Andrew Bell <<a href="mailto:andrew.bell.ia@gmail.com" target="_blank">andrew.bell.ia@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Mar 25, 2019 at 2:49 PM Matt Beckley <<a href="mailto:beckley@unavco.org" target="_blank">beckley@unavco.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div>Is there more information available regarding how the 'resolution' keyword works for the latest version of readers.ept? Is it "gridding" the data at a specified cell size?</div></div></blockquote><div><br></div><div>The EPT format is essentially an octree of point data. The resolution options essentially tells the reader how far to descend the tree when fetching data.</div><div> </div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div> If so, how does it handle nominal class data such as lidar classifications? Is it taking the first, last, or a random sample to assign as the classification for each cell(assuming a scenario where there are multiple classifications that fall within a given cell). In other words, how is the defining classification assigned for each cell given a sample of points with varied classification values?</div></div></blockquote><div><br></div><div>The resolution option is unrelated to point classification, so I'm not sure that I understand your question. Perhaps you can provide some more detail or an example.</div><div><br></div></div>-- <br><div dir="ltr" class="gmail-m_-5118659665164687995gmail-m_-5011325440620476816gmail-m_-7683089810198383044gmail-m_555617595015237444gmail-m_3918760174153493323gmail_signature">Andrew Bell<br><a href="mailto:andrew.bell.ia@gmail.com" target="_blank">andrew.bell.ia@gmail.com</a></div></div>
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