Scaling working units from meters to feet

[Wes Toews]

Hi, I have what is likely a dumb problem but I can't seem to scale working units from meters to feet?

Ultimately what I'm trying to do is use "-proj_epsg 26910 2286" to reproject from utm10 to state plane survey feet. This transforms from meters to feet horizontally, but not vertically.

The older method, "-epsg 26910 -target_epsg 2286" scales horizontal and vertical to feet, that's fine. But I want to use the new method.

But even as a postprocessing step to correct the vertical units, I can't seem to get -target_elevation_survey_feet to work - it does nothing, even if I explicitly define the input-output units like so: "-elevation_meter -target_elevation_feet", or a bunch of more complicated variations. And even without a projection change, just trying to change meters to feet, this doesn't seem to work either.

A small sample file is attached, and I've tried this on a slightly old version as well as a more recent version.

Thanks!

[Jochen Rapidlasso]

Hi Wes,
thanks for the sample. As soon as you use the proj library all CRS calculation is done there. It is not possible and not intended to use a mix of both.
Your "-proj_epsg 26910 2286" conversion does just a horizontal projection. This is right by definition.
This is what we tried to solve your problem:
    lasinfo64 -i superclip_meter_1.laz
Shows you have some Riegl stuff and a coord-fluff (x10) we do not want to have for testing, so we clean first:
    las2las64 -i superclip_meter_1.laz -o tmp1.laz -remove_all_vlrs -rescale 0.01 0.01 0.01

:: tmp1.laz
min x y z:      537,167.23 5,029,460.77 70.90
max x y z:      537,178.57 5,029,481.35 79.50
range x y z:    11.34 20.58 8.60

We do the PROJ conversion
    las2las64 -i tmp1.laz -o tmp2.laz -proj_epsg 26910 2286

min x y z:      1,120,407.22 37,433.48 70.90
max x y z:      1,120,446.52 37,502.05 79.50
range x y z:    39.30 68.57 8.60

And to compare a LAStools conversion

las2las64 -i tmp1.laz -o tmp3.laz -epsg 26910 -target_epsg 2286
min x y z:      1,120,407.22 37,433.48 70.90
max x y z:      1,120,446.52 37,502.05 79.50
range x y z:    39.30 68.57 8.60

Both looks the same (while the WKT differs in detail, but this is not the subject here)

Using LAStools we can also to a elevation conversion in one step:

las2las64 -i tmp1.laz -o tmp4.laz -epsg 26910 -target_epsg 2286 -target_elevation_survey_feet -set_ogc_wkt
min x y z:      1,120,407.22 37,433.48 232.61
max x y z:      1,120,446.52 37,502.05 260.83
range x y z:    39.30 68.57 28.22

To use PROJ and do a vertical correction we use a simple trick: We use mathematics, and not CRS conversion.
The factor for meter to survey feet is 3.28..., we can do this in a one step together with PROJ:

las2las64 -i tmp1.laz -o tmp5.laz -proj_epsg 26910 2286 -scale_z 3.2808333333

This should do the job.

Cheers,

Jochen @rapidlasso