HUGE PTX FILE SIZE

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KMack
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HUGE PTX FILE SIZE

Post by KMack »

I just created a PTX file for 59 scans from Cyclone Core. Its not unified because I need to show realviews (the mirror balls) in Recap. PTX is the only format I know which keeps the scan locations in order to show the 360 views. The file is huge 256GB. I decimated the point cloud 5 mm upon Recap import and saved as an RCP - the file size went down to 80GB.

Any idea how to reduce file size prior to export from cyclone core?

Also is a ptx always un-unified ? or can you export a unified ptx? (Please excuse my ignorance!)
Last edited by KMack on Tue Mar 10, 2020 1:21 am, edited 1 time in total.

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Re: HUGE PTX FILE SIZE

Post by Steve_Euclideon »

What file format are you hoping to export as ? PTX?
Once exported what do you want to do with that Point Cloud?

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Re: HUGE PTX FILE SIZE

Post by smacl »

PTX can be a very inefficient format based on the number of places of decimals you're using, so in the example below we're using 38 bytes per scanned point for data without RGB

17.168756 11.199326 3.575297 0.180011
17.178024 11.205400 3.620054 0.175601
17.177233 11.204914 3.661788 0.184802
17.171070 11.200925 3.702663 0.180011
17.162424 11.195314 3.742929 0.183612
17.158886 11.193036 3.784855 0.182010
17.153275 11.189406 3.826196 0.199207
17.153913 11.189582 3.868035 0.199603
17.136919 11.178527 3.906395 0.196002


In a format like LAZ this will be about 5-7 bytes, same for our own SCC software. Not sure if it is an option in your software but simply reducing to 3 decimal places gives almost a third size reduction. At a guess, using LAZ instead of PTX would change your 256GB to 41GB for the same representation. Have a look at Pointzip http://www.cs.unc.edu/~isenburg/pointzip/

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Re: HUGE PTX FILE SIZE

Post by stevenramsey »

KMack wrote:
Fri Feb 28, 2020 1:35 am
I just created a PTX file for 59 scans. Its not unified because I need to show realviews in Recap. The file is huge 256GB. I decimated the point cloud 5 mm and saved as an RCP and the file size went down to 80GB.

Any idea how to reduce file size prior to export from cyclone core?

Also is a ptx always un-unified ? or can you export a unified ptx? (Please excuse my ignorance!)
lets take each of those questions one at a time

If you decimate a pointcloud it will always reduce but you wont be able to export PTX

You can reduce each scan by a factor of 4 and Keep PTX compatibility but you may as well scan at a lower resolution


PTX is special (if a file format can be special)
you can have individual files per scan or one file containing many scans
All scans in a PTX file are based around the scanner origin which is 0,0,0 with a full registration transformation matrix as the header.
A PTX file has all colums always full so it is always z y z I R G B and if a point doesn't exist will be populated with Zeros.
The reason for this is that it allows for a full round robin import export from any system able to read it (unlike E57)

For the sake of aurgument if you printed the file out and put it in long term storage (we store paper better than digital) in 100 years it can be typed back in and would produce an Identical pointcloud as you exported.

So yes PTX is huge but the most flexible and open format there is
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Re: HUGE PTX FILE SIZE

Post by jedfrechette »

If you're mostly concerned about the size because of storage requirements keep in mind that being text, ptx files tend to compress pretty well. That 256 GB file is probably more like only 50 GB if you just zip it up and other compression schemes can do even better.
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Re: HUGE PTX FILE SIZE

Post by Carbix »

why not e57. Its way smaller. Only value I have seen with PTX is that you can range filter in ReCap.
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Re: HUGE PTX FILE SIZE

Post by landmeterbeuckx »

Besides the question is this a nice discussion. Maybe a list of formats and it's best purpose would be great.

I mainly use the laz format because of it's size. Ptx sometimes for bubble views in recap when asked.
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Re: HUGE PTX FILE SIZE

Post by jedfrechette »

Carbix wrote:
Tue Mar 03, 2020 6:38 am
why not e57.
One reason I like ptx is that it is simple. When you ask someone for a ptx file you know what you're going to get. Ask for a structured e57 file and half the time you still get an unstructured file, followed by an email thread trying to explain the difference.

I like e57 as a format, but in retrospect it probably would have been good if they did more to distinguish the different variants.
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Re: HUGE PTX FILE SIZE

Post by smacl »

landmeterbeuckx wrote:
Tue Mar 03, 2020 6:54 am
Besides the question is this a nice discussion. Maybe a list of formats and it's best purpose would be great.

I mainly use the laz format because of it's size. Ptx sometimes for bubble views in recap when asked.
I'm also a fan of LAZ as it is compact, reliable and fast. I also like that it preserves classification to a greater or lesser extent depending on which version of the LAS specification it is based on. Most importantly perhaps we've Martin Isenberg at LASTools maintaining a great open source library for LAS I/O making sure the latest standards are updated and available to all.

E57 and PTX offer the advantage of setup information details for terrestrial LIDAR and E57 can also include embedded photography though it doesn't seem that widely supported. The reference implementation of libE57 for developers is also free but slow and hasn't seen an update since 2012. As a structured format, apart from huge file sizes, PTX also lacks classification so is lossy by comparison to LAS.

PTS gets a lot of flak but has the great advantage of being that simple it will work with anything. While file sizes are big, they zip down well enough.

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Re: HUGE PTX FILE SIZE

Post by KMack »

Hi All,

Thanks for the feedback.

The processing software is Cyclone (we use both core and register 360).

I used e57 as my standard output go to. But when I am required to produce realviews(otherwise mirrorballs) in recap then i need an output format which retains individual scan positions so the realviews with the 360 photos can be generated.

So in this instance a .ptx is unavoidable - unless anyone has a suggestion for any alternative cyclone-exportable file format that enables realviews after index in Recap?

Thanks
Kirsty

P.S - I just posted this about getting 360 images (not point cloud) in realviews which is what i got the ptx file for... https://laserscanningforum.com/forum/vi ... 49&t=15991

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