LAS CRS usage in non-mapping/purely-local applications

[esilvia]

I recently heard that JPEG is working on publishing yet another ISO point cloud format: http://ds.jpeg.org/documents/jpegpleno/wg1n86012-REQ-JPEG_Pleno_Point_Cloud_Use_Cases_and_Requirements_v1_3.pdf

This made me realize (again) that LAS is tuned for remote sensing mapping applications, and that's not more obvious than in the CRS requirement for a "valid" LAS file. This requirement as commonly understood doesn't make sense for point clouds at the handheld scale (e.g., 3D printing, facial scans, localized TLS scans) and it's unclear how one might "properly" encode the CRS for such "purely-local" applications and still be valid.

Is there a canonical way to encode WKT with a purely-local CRS (referenced to 1000,1000 or even the scanner itself), or do we need to add one?

(Thanks to to @mjolsen for bringing this to my attention)

[esilvia]

I should add that my understanding is that those needing purely local CRS definitions generally omit the CRS VLRs altogether, which of course produces a technically invalid LAS.

[kjwaters]

Evon, I didn't dig very far into this, but I think there may be a way. I believe an engineering CRS is what you're looking for. http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#60

Kirk

On Mon, Aug 31, 2020 at 11:41 AM Evon Silvia notifications@github.com wrote:

I should add that my understanding is that those needing purely local CRS definitions generally omit the CRS VLRs altogether, which of course produces a technically invalid LAS.

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[vminor]

Evon and Kirk,

It might be better to look at the CRS definition (the CS is basically just the Axis description).

http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#92

Using that, this is what an "Engineering CRS" might look like for a given sensor:

ENGCRS["A Specific Sensor CRS", EDATUM["Wand center location", ANCHOR["Center of System : Right Corner marker Prince Albert Hall"]], CS[Cartesian,3], AXIS["(x)",X], AXIS["(y)",Y], AXIS["(z)",Z], LENGTHUNIT["meter",1.0] ]

One note, the Engineering system exists in the WKT version 2 specification (ISO 19162:2019) but it's probably not going to be recognized by many software packages on the market that read WKT (it ain't 'GIS'). Additionally, it is probably important that the Datum be something unique for each survey, unless all of the constraints and parameters match a previous collection. If the above definition was used in every custom local survey the implication is that all of the data is in the same coordinate space, which would not necessarily be true.

Victor

On Mon, Aug 31, 2020 at 1:35 PM Kirk Waters notifications@github.com wrote:

Evon, I didn't dig very far into this, but I think there may be a way. I believe an engineering CRS is what you're looking for. http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#60

Kirk

On Mon, Aug 31, 2020 at 11:41 AM Evon Silvia notifications@github.com wrote:

I should add that my understanding is that those needing purely local CRS definitions generally omit the CRS VLRs altogether, which of course produces a technically invalid LAS.

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[esilvia]

@vminor Not sure how I missed this post. Thanks for the contribution that directly answers my question!