Point clouds, coordiante systems & positioning

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    Wishgranter
    Hi ross.havery
    Contact me directly at my email for the barymetry data etc.

    My aim is to create and export point clouds of 5cm or better resolution with positional accuracy of +/- 2cm (but preferably as good as possible) I know these are dependant on the amount of photos and ground control points but I just wanted to give you an idea of what im trying to achieve.


    can be done...

    - when importing photos with geographic positions in GPS (WGS 84) can you then translate these to OSGB Grid?


    yes, if you set a proper COORDINATE SYSTEM for the project, then it will be transparently converted
    the OSGB is in the EPSG system under EPSG:27700 http://spatialreference.org/ref/epsg/os ... onal-grid/

    - If you have OSGB36 grid coordinates for the control points, can you import them as grid coordinates rather than having to change them all to Latitude, Longitude values?

    Yes just change the importer setting from "Lat, Long, Alt" to "X, Y, Alt" format..

    - when exporting the point cloud if I export in OSGB36 the XYZ file gives completely wrong values and when imported into another programme only shows a single line of data.


    This is because you did not set the proper PROJECT COORDINATE SYSTEM = WORKFLOW= SETTINGS = project coordinate system, best when you set this before you start importing data...

    - If I export in WGS UTM 31N then the data does come out in the correct place but the easting values are all truncated to the nearest 10cm so you get a stripped effect in the data, this may be due to each column in the XYZ file being limited to 8 values?


    Need to check this, is it possible to get the sample dataset ?
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    ross.havery
    Hi Wishgranter,

    Thanks for your response, I will contact you on email later about the bathymetry datasets as well as sending you a sample export of the WGS UTM 31 issue, as well as the E57 issue I posted in the other forum.

    Thanks for your response on the other issues these have helped a lot. I have another couple of questions if that's ok.

    - first if I set my project to OSBG36 - British national grid and then take my photos in (GPS WGS84) then these re-project fine as you said previously but the altitude of the file changes by 45.29m. I think this is due to the conversion wanting the Altitude of the photo to be in ellipsoidal heights and then when it converts it to the project coordinates it changes this value. Is there a way to stop this as the altitude in the photo files is already in the correct orthometric height? or is there a way to turn the altitude attribute off on the photos completely and just use control points.

    - secondly at the moment I am bringing in control points manually then finding each point in the photos etc. I see under the workflow tab there is an option to bring in a whole ground control file. Please could you explain how this data is collected and imported as I see the first header should be name, is this the name of the photo and if so is it the position of the camera that's the ground control or something the camera is imaging.

    Thanks again for all you help.
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    Michal | CR
    Hi thank you for the post.

    It is hard to answer the first question. I assume that you need to send the data to Milos and he can look at it and let you know.

    Yes you can import ground control file. It will create new control point for each line with proper settings. If you have also measurements ( image, x, y, control point ) then you can import them as well but just in CLI version using 'importControlPointsMeasurements' command.
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    Lucia CR
    ross.havery wrote:
    at the moment I am bringing in control points manually then finding each point in the photos etc. I see under the workflow tab there is an option to bring in a whole ground control file. Please could you explain how this data is collected and imported as I see the first header should be name, is this the name of the photo and if so is it the position of the camera that's the ground control or something the camera is imaging.

    You can find more information on ground control points import in the Help section directly in your RC, providing that you have updated it since 9 July.
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