columns name in ascii file of export points cloud

[mfran2002]

Hello,
exporting the points cloud I get an ASCII file.

I use these two options:

File > Export Points... > option "XYZ Points Cloud"

File > Export Points... > option "ASCII pts"

May someone tell me the meaning/name of the columns in those files?

Thank you all!

[Alexey Pasumansky]

Hello mfran2002,

For ACSII PTS the columns have the following order: X, Y, Z, R, G, B, I
where I is color intensity.

For XYZ points file format it would be X, Y, Z, R, G, B, Nx, Ny, Nz
where Nx, Ny and Nz are components of point normals vectors.

Saving color and point normals is optional.

Altitude values for georeferenced chunk is expected to be height above ellipsoid, unless coordinate system used is based on different geoid model.

[mfran2002]

thanks Alexey.
I use the following coordinate system:

WGS84 UTM Zone 32N

I've some doubts, following an example:

photos into photoscan report height_Cameras_into_Photoscan=220mt

the photos was taken by a drone at a height_Drone=120mt

the ASCII file export points cloud record height_ASCII=99mt

so, everything sounds good (200 - 120 = 100 very near to 99)

but when I check the real altitude, for example via tools like "map tool" (www.zonums.com/gmaps/maptool.php), I obtain a value very far from 99mt:

height_MAPTOOL=80mt

and I don't know how to justify it...
may you have some ideas?

thanks

PS: another example:

height_Cameras_into_Photoscan=95mt

height_Drone=60mt

height_ASCII=36mt

BUT:

height_MAPTOOL=105mt (very very far from 36mt)

[Alexey Pasumansky]

Hello mfran2002,

Which values you are passing to PhotoScan as altitude of the camera positions? Are they height above ellipsoid or haight above take-off point or sea level? Only the first option is correct, while others will give you incorrect referencing results.

[mfran2002]

Hello Alexey,
the altitude of the camera positions are automatically reported by Photoscan, I do not pass the altitude.

After having imported the photos into Photoscan I automatically see the altitude (and the values I see are the ones I reported in the examples below, named "height_Cameras_into_Photoscan").

You mean there is a way to force, into Photoscan, the altitude of the camera positions?

[Alexey Pasumansky]

PhotoScan loads the coordinate information from the EXIF header of the imported images. But if you have camera altitude values in the second example lower than height_MAPTOOL value, then I assume the altitude values written to EXIF by drone are above take-off point.

[mfran2002]

But  the altitude  above take-off point should be:

height_Drone...

Do you know where the altitude inside the .txt (or .pts) file (output from export points cloud from Photoscan) is taken (in the example below named height_ASCII)?

[Alexey Pasumansky]

Hello mfran2002,

I don't yet understand, which altitude is written to the images as camera position.

In your example height_cameras_to_PhotoScan is below height_maptool elevation that seems to mean that the drone was flying beneath the surface, which is obviously incorrect. Do you have any information about telemetry data written by the drone?

[mfran2002]

Alexey, you are absolutely right, I've not explained well the example.

My drone was flying at an altitude (respect to the takeoff point) of 60 meters:

height_Drone = 60 mt

After the fly, I've loaded my photos into Photoscan and I've processed them, obtaining the mesh.

Into Photoscan, at "Ground control" tab, "Cameras" section, I see all the attributes of my photos, and the altitude reported is 95 meters:
 
height_Cameras_into_Photoscan = 95 mt

After that, I exported the points cloud (trying both "XYZ points cloud" and "ASCII pts" file type) and the altitude reported into the ascii file was 36 meters:

height_ASCII = 36 mt

The altitude reported, in the same area, by maptool2, was 105 meters:

height_MAPTOOL = 105 mt

[Alexey Pasumansky]

Hello mfran2002,

Then the question is why height_Cameras_into_Photoscan = 95 mt. PhotoScan just reads the data from image EXIF to obtain this info. It means that this information is kept in the images themselves even before loading them to PhotoScan,