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Author Topic: Export points cloud  (Read 15670 times)

mfran2002

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Export points cloud
« on: June 08, 2016, 02:48:04 PM »
Hello,
after having processed my photos with photoscan (I'm now working on photogrammetry), I should need to export a file to be elaborate by another software to return "level curves" and volumetric data.

Therefore I need a file containing all the points cloud (mandatory containing: altitude, latitude, longitude)

I would need to know what is the photoscan function to get this file, maybe:

File > Export Points... > save as file type "XYZ Point Cloud"

is it correct? or have I to choose another way?

thanks!
bye

HMArnold

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Re: Export points cloud
« Reply #1 on: June 08, 2016, 05:45:33 PM »
I regularly use the steps you mention to get the point cloud in text format using the "ASCII PTS" option.

Be aware that unless you increase the number of digits of accuracy on the export, the points get rounded off significantly so that you get all the points on a grid with large square gaps in between. I use 9 digits of accuracy.

The files tend to be quite large and can be difficult to work with.

Photoscan has the ability to calculate elevation contour lines and do enclosed volume calculations directly.

mfran2002

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Re: Export points cloud
« Reply #2 on: June 08, 2016, 06:15:41 PM »
absolutely thanks HMArnold!
is it possible to choose between sparse and dense cloud?
and, just to be sure: the 3rd column, the altitude of each point of the cloud, is AGL right?
« Last Edit: June 08, 2016, 06:57:28 PM by mfran2002 »

HMArnold

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Re: Export points cloud
« Reply #3 on: June 08, 2016, 07:17:43 PM »
That's a difficult question because it depends upon several things, including the coordinate system you choose and whether or not you use GCPs with exact altitude values.

As near as I can tell the altitude values in the EXIF info for each image from a Phantom Pro 3 comes from the GPS altitude recorded during the flight and comes in as Feet Above Sea Level. Those values appear to be accurate relative to each other but can be off by hundreds of feet on any single mission. P3P units not sold in the US might be set to export the altitude values in meters, which would be much more useful.

My experience has shown that using the AGL value for each image makes much more sense, and you can get those values from the P3P flight log info. I use the Ultimate Flight App which gives me not only a repeatable and accurate altitude value but also the heading (yaw) and gimbal angle if you need it.

Converting those values all into meters and creating an import file means that everything goes into the alignment process in meters.

Since I don't use GCPs, the alignment process and all subsequent calculations and exports are done using AGL.

If GCPs were used, and you chose the export coordinate system as WGS 84, I assume the elevation values would come out as meters above sea level.

For volume calculations in my applications, as long as the elevation values are accurate and repeatable relative to each other, I'm not sure the difference between AGL and ASL matters.

A gravel pile with a given set of dimensions and geometry would have the same volume whether it was on the sea shore or in the mountains.


mfran2002

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Re: Export points cloud
« Reply #4 on: June 08, 2016, 07:38:03 PM »
I would use the GCP and export coordinate system as WGS 84.
Concerning the app, I use the iOS app "Map Pilot".

May you please tell me what are the meaning of the columns in the "ASCII PTS" file?

Surely it starts with longitude, latitude and altitude...

HMArnold

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Re: Export points cloud
« Reply #5 on: June 08, 2016, 07:49:05 PM »
Afraid I can't help you there

I only use the Lat/Lon/Elevation values

mfran2002

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Re: Export points cloud
« Reply #6 on: June 08, 2016, 07:58:26 PM »
ok Arnold, very very thanks for your precious help!

just a last question: do you know what's the meaning of the 3 textboxes named "SHIFT" I find in the export points mask?
« Last Edit: June 10, 2016, 11:18:09 AM by mfran2002 »

Alexey Pasumansky

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Re: Export points cloud
« Reply #7 on: June 10, 2016, 01:48:43 PM »
Hello mfran2002,

Shift fields allows to subtract large values from the corresponding coordinates. For example, can be applied when dealing with UTM systems.
Best regards,
Alexey Pasumansky,
Agisoft LLC