las2shp

[Möst, Karin (LDBV)]

Hi Jochen,

we have a special workflow, where we want to convert las to shape, edit the shape in a GIS and then go back to las, to copy a different classification to the original las points (lascopy).
Unfortunately the necessary attributes (GPS-time stamp and return number) are not preserved when converting from las to shape.
Is there maybe an intention to implement this (keeping several attributes/information) or will there be no further development for las2shp and back?

Thanks
Karin

[Jochen Rapidlasso]

Hi Karin,

the focus of LAStools is in pointcloud, and the shp format is not a nice one.

So we always try to keep closer on LAS/LAZ side than on SHP side.

Anyway, If this is a demand we will try to solve that problem.

Please define your problem in a detailed small workflow with some small samples so I understand and can simulate what you are doing or plan to do.

I will try to find a solution then.

Thanks,

Jochen

[Möst, Karin (LDBV)]

Hi Jochen

 

we try to find high and low noise points (outliers, birds, incorrect reflections on roof windows….).

 

first we use lasheight to calculate the height above ground

 

Then we use several filters e.g. and set the classification of the filtered points to 0

 

las2las.exe -i *_1.laz

                   -drop_last_of_many

                   -keep_class 20

                   -keep_z 45 100

                   -keep_intensity_below 20

                   -set_classification 0

                   -odix _first20_between45-100

                   -olaz -cpu64 -cores 6

 

 

To check and edit the result (maybe there are some powerlines we want to keep in class 20) we convert the points to shape and edit the result in a GIS (this is, we remove the falsely classified points from the shape to keep only real the outliers. Tthis works nicely in a GIS, where we can see the powerline route e.g.)

 

Then we convert the shape back to las and with lascopy copy the classification (0) to the real outliers.

 

I hope, this is not too confusing.

 

Thanks

Karin

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[Jorge Delgado García]

Hi Karin,

First, I can recommend you the use of LASnoise, which is the LAStools module for noise detection. Have you used it?

Second, I don't think there should be a problem, at least on the LAStools side, you can include the GPStime as an attribute in the Shapefile, which should be kept in your GIS when you do the edit (I particularly don't recommend it considering the files own size, even I would do it in the LASview itself if it's little), and the key is that as you go back to the LASfile. 

If you import directly with SHP2LAS you will not keep the information since it is not logical that a SHP file has GPStime information (really I don't know if SHP2LAS is prepared for import GPStime from a SHP file), so maybe a possible solution is that you export in your GIS to an ASCII format, and then use TXT2LAS considering in the import the GPStime.

I don't know if this is more or less clear.

With which GIS are you doing the operations? Could you send me an example, if it is a GIS to which I have access perhaps I can to improve my idea.

Jorge

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[Möst, Karin (LDBV)]

Hi Jorge,

 

as a matter of fact, up to now we used the text-format. I wanted to reduce the steps and to shorten the workflow. Normally there are only few points that are misclassified.

 

We have QGIS and ArcMap. For you, QGIS should be ok.

And yes, we use lasnoise, too.

 

Thank you

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