CyArk Updates Web Browser

A key part of CyArk’s mission is the “free dissemination of rich 3D content from cultural heritage sites.” Liz Lee reports that by taking advantage of recent advances in web technologies their completely redone web browser now provides the ability to┬árotate, cut, and measure 3D point clouds and mesh models all within an internet browser – impressive.

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One Response to CyArk Updates Web Browser

  1. Hello,

    Congrats to CyArk for creating this wonderful interactive online experience.

    As I am very involved with point cloud formats I was instantly curious about how CyArk’s 3D Viewer was storing these point clouds – after all, users will have to download them. Turns out that each model is stored as several gzipped ASCII files that are around 2 MB in size and contain a JSON string that describes the point cloud. The Tikal Temple I model, for example, is stored in 5 files that total 10.8 MB (see links at the very end).

    On further inspection I saw that each file contained a list of points as [x,y,z,"RGBintensity", "RGBcolor"]. Here are the first six points from the first file of the “Tikal Temple I” model:

    [28.286682500009,-17.910553000169,-22.492218,"00ff13","473618"]
    [-29.050201500009,19.081512999721,-20.314026,"f56400","958b4e"]
    [-29.855194500007,19.4510499998,-20.298309,"f56700","938749"]
    [-29.754943500011,19.124969999772,-20.32785,”f98100″,”9c9255″
    [-29.297363499994,19.565826999722,-20.301452,"e91700","9a914f"]
    [-29.503723500005,19.244445999851,-20.305786,"fcb500","958b4b"]

    I suggested to the CyArk group to be a little less generous with the decimal digits and store something more compact instead by rounding to millimeters:

    [28.287,-17.911,-22.492,"00ff13","473618"]
    [-29.05,19.082,-20.314,"f56400","958b4e"]
    [-29.855,19.451,-20.298,"f56700","938749"]
    [-29.755,19.125,-20.328,"f98100","9c9255"]
    [-29.297,19.565,-20.301,"e91700","9a914f"]
    [-29.504,19.244,-20.306,"fcb500","958b4b"]

    Millimeter accuracy should be more than sufficient for a laser scanned temple. The answer I got was that they had considered that shaving a few digits would give some savings but that they “[...] generally don’t round anything. Any loss of quality, no matter how academic, is usually frowned upon around here.”

    I would like to take this as an educational opportunity on scanner precision. (-: Folks who have seen the first 5 minutes of my LASzip LiDAR compression video know that I have been on “a mission” to educate folks about not storing excessive precision in their scanned 3D data. (-:

    Why excessive? The majority of the decimal digits that CyArk stores in those files are not actual data. The binary IEEE format that is used to represents a double-precision floating-point number often makes it seem as if there are many non-zero decimal digits … but most of them are completely meaningless.

    How meaningless? CyArk stored the x and y coordinate for the points of the “Tikal I Temple” with picometer (!) precision (see illustration below) and let me quote wikipedia: “The picometre’s length is of an order such that its application is almost entirely confined to particle physics and quantum physics. Atoms are between 62 and 520 pm in diameter.” So clearly a bit of any overkill … (-:

    28.29 = centimeter
    28.287 = millimeter
    28.2867 = 0.1 millimeter
    28.28668 = 0.01 millimeter
    28.286682 = micrometer
    28.2866825 = 0.1 micrometer
    28.28668250 = 0.01 micrometer
    28.286682500 = nanometer
    28.2866825000 = 0.1 nanometer
    28.28668250001 = 0.01 nanometer
    28.286682500009 = picometer

    Here is a link to my version of the “Tikal I Temple” in good old VRML. It is displayed in the ancient Java Engine from Shout3D so it may not show on your Mac (but on your Solaris Sparc) but you can still download the model. It is only 3.8 MB instead of 10.8 MB because I store centimeter instead of picometer precision.

    Part of my “campaign” (*) was the release of pointzip for compressing terrestrial scanned data. It features a precision selector very prominent in the GUI that “forces” the user to make a choice and reflect about the precision in the data.

    Regards,

    Martin @lastools

    (*) This message was brought to you by the people for better 3D compression through storing less decimal places by knowing your precision.

    JSON file 0 file 1 file 2 file 3 file 4

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