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Tree Delineation Extractor

Details provided by Kunxuan:-

Question (Smruti): Earlier I have sent you the working tree delination script (working_tree_delin_workflow_OSBS.py). While reviewing the script, Jong and I observed that lines (124 – 127) are independent of the rest of the above code. It takes two input files (v2014_OSBS_1_400000_3279000_dsm_tif and v2014_OSBS_1_400000_3279000_dtm_tif) and outputs (OSBS_01_chm_tif). As per the ppt that you have sent us earlier, the output of tree delination is a text file with tree centers and radii. In the line 120, the script outputs tree.csv file with this information.  So, we are trying to understanding if lines (124-127) are required for the tree delination workflow?  

As per your previous email description: “In the script, there are two different canopy height models (CHM). One is a product that came with the data, the other is calculated from the DSM and DTM which are extracted from the point cloud data using LASTools. The script currently use the first one, which is nicer, to perform tree extraction.”

Is it the case that the input file (v2014_OSBS_1_400000_3279000_CHM_tif) and the file (OSBS_01_chm_tif) are the two different CHM that you were mentioning above? So, can we use either one as input to the tree delination workflow?

I have attached another script (tree_delin_workflow_2.py), where I am using (OSBS_01_chm_tif) as the input to the tree delination workflow.

The results are different in both cases.

Answer (Kunxuan):

This point was also discussed in the meeting we had a while back.

You are right in that the lines you mentioned are independent, and not needed for the script to work.

The two CHM files theoretically represent the same thing. The current script uses a CHM file that comes with the data as a processed data product.

For some data sets, this product might not exist. So Jong wanted me to include steps on deriving this product from data that every dataset should have, which is what lines 124-127 are doing. These steps should theoretically come before everything else to produce the CHM file that is used as input for the entire workflow.

The difference between the v2014_OSBS_1_400000_3279000_CHM_tif and OSBS_01_chm_tif is that the first is produced by the company who processes the data and they have their own algorithm and filters that makes everything “nice”. The second is doing simple subtraction without any filters or smoothing, leading to less processed version of the same data. Therefore results should be different, but not by too much.