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Thread: Dealing with artifacts in Wilbur

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      acrsome is offline
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    Default Dealing with artifacts in Wilbur

    My current project is mapping a terraformed Venus- see my WIP in the world/regional forum. I found the MIT topo image- based on Magellan data- for the planet as a grayscale image and loaded it into Wilbur (my first time using Wilbur). I figured using Wilbur might be easier than the hand-drawn stuff I'm transcribing from the USGS topo map of the planet. But the MIT data has some odd artifacts:

    Dealing with artifacts in Wilbur-betawilbur.png

    This is one small area to give you an idea of what I'm talking about. My question is, as a new Wilbur user, Wilbur seems to be able to do a LOT of cool stuff, but I have no idea even where to begin. Hell, I'm currently working on how to set a sea level...

    How can I get rid of those streaks at the left third of the image that Wilbur reads as higher elevations?

    How I can extrapolate in a reasonable fashion into the blank spots in the data, like that bit in the upper left? (There are much larger ones elsewhere.)

    The grayscale apparently maxed out too low as well- the higher elevations all look like perfect plateaus, as you can see. I'll have to deal with that somehow- probably by hand modifying from the satellite images or something. But that's lower on the priorities I think.

    Or would it be better to manipulate the original grayscale image in GIMP or something?

    Thanks, All.
    Last edited by acrsome; 04-27-2014 at 07:47 PM.

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      waldronate is offline
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    Without knowing what data you used, I can't offer you any suggestions about the apparent height clipping. If it's in the imported data, then there's nothing that Wilbur can do about it.

    The streaks are in the original Magellan data; you'd need to paint that out by hand. Painting in Wilbur is a bit of a pain, especially for the kinds of curve that you'd need to paint along. On the other hand, Wilbur does allow raising and lower of the data, which is probably the sort of thing that you want for that kind of work.

    Wilbur does have a (very) limited tool for healing imported SRTM data, but I think that the nature of the gaps will probably prevent it from working well in a lot of cases. The SRTM holes tend to be fairly small and without straight edges; the Magellan data has holes with straight edges that are fairly large.

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    And Sea Level is a property of the shader: Use Texture>>Shader Setup and pick the Altitude tab. Enter your desired altitude in the box labeled "Sea Level".

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    I used the GTDR data set, which was originally complied by MIT, and yes the streaks are in the original data. Essentially, it was a large grayscale JPG file. I changed it to a PNG per your suggestion to get Wilbur to load it. I found it in cylindrical projection on an astrogeology website, so that I can now churn it through G.Projector. Score! (The raw files available from NASA are all Mercator, sinusoidal, or polar projections. Grrr.)

    I could certainly send it to you if you like, but I guess you've answered my question already. Answer = yes, it will involve meticulous manipulaiton by hand. Sigh. I guess I have a project for the next six months...

    Thanks for the sea level pearl. I'm kind of wading through your neat little program at a very slow rate. I know so little about mapping that I end up going to the (dated) pdf manual or wikipedia a lot. I guess I'll start by playing with the sea level , and then see just how much of those streaks I have to deal with- many may be under water.

    Thanks, again!
    Last edited by acrsome; 04-28-2014 at 11:53 AM.

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    Post the image - I may be able to help there.

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      acrsome is offline
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    I'm not sure if I can. I's 32MB, and isn't there some sort of forum size limit here?

    Nonetheless, when I get home I'll see if I can put it in googledocs or some other filesharing thingy or something. (Which I've never done before, so bear with me.)

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    Whats the URL of the original MIT / astrogeology website file then ?

    Can you import these files instead ?
    http://pds-geosciences.wustl.edu/mgn...002/gtdr/merc/
    Last edited by Redrobes; 04-30-2014 at 10:43 AM.

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      acrsome is offline
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    That's the data, yes. Those are the original GTDR data files I mentioned. (As I'm sure you know, you were in the mercator directory, but sinusoidal and two polar projections are avaialble in a higher directory.)

    I suspect that these streak artifacts are in this data too, since my file is just one large stitched-together image of the same data. I stumbled upon a site that would export them as one large jpeg in cylindrical projection for me. That's where I got mine, since cylindrical is more useful, being able to load into G.Projector and all. (I am far too ignorant to manipulate those files into an equirectangular cylindrical projection on my own. And I'm also not sure how to change the CD images into a useful file format.)

    USGS Map-A-Planet

    This was the website I used to order the jpeg. You have to dig around a bit to figure out how to order it at the resolution and in the projection that you want. The original GTDS data is about 4.6km/px, so that's what I ordered. It takes them about a day to put the jpeg together for you and email the download link (which is only good for a few days).

    I also took a closer look at my stitched-together cylindrical image in Wilbur last night, and there are many more subtle north-south streaks all over the place. I think I have a lot of work ahead of me.



    EDIT--- I just re-ordered another version from Map-A-Planet, this time in 16-bit TIFF rather than 8-bit JPG to hopefully get more detail in elevations. (See how much I've learned already?) When I get the link I'll post it here for others to download.



    EDIT AGAIN-- Well, you got me thinking about this again, so I was poking around the ISIS forums and found this:

    ftp://pdsimage2.wr.usgs.gov/pub/pigp...ar_properties/

    It looks like there is some sort of topo data in that directory, too, but it is again beyond me. What's frustrating is that I suspect that cleaning up this data and producing a decent image at that resolution would be trivial for some of these astrogeology guys, but I'm struggling. But then, I guess I don't have their resources, eh?

    There is also something called the RDRS spherical harmonic topography model available:

    http://pds.nasa.gov/ds-view/pds/view...5-TOPO-L2-V1.0

    http://pds-geosciences.wustl.edu/mgn...l2-v1/mg_5201/

    From the description in the first link this might actually be nice data, but I just can't figure it out. And I have no idea what the resolution is, projections, file formats, etc. But the filesizes are quite small, so I suspect that the resolution is poor, and I moved on.
    Last edited by acrsome; 04-30-2014 at 02:47 PM.

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    Wow, that was fast. Here's the link to download that TIFF I just ordered:

    Planetary Data System - Map-a-Planet

    Warning: it is 54.1MB, and the link is only good through May 4th. But it looks like it preserves the elevation data that was lost on my last attempt- no plateaus on all the higher mountaintops. Still has the streaks, though. I'll look at it in Wilbur when I get home.

    EDIT--- Huh. Wilbur doesn't read TIFFs. I have to convert it into a PNG, and I do that in GIMP, which can only handle 8 bits, so I lose some data anyway. The contours look very pixelated. I'll start hand-correcting what I have, unless Redrobes manages to produce a miracle for me...
    Last edited by acrsome; 05-02-2014 at 04:02 PM.

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    For anyone who cares- it is a heck of a lot easier to patch blank spots in the data with the clone tool in GIMP than in Wilbur. Once I get this done I'll work on the streaks, which I suspect will be the opposite- easier to manipulate in Wilbur.

    Say, what's the difference between simple cylindrical and equirectangular cylindrical? My google-fu is failing me. Near as I can tell they are the same, but my simpe cylindrical images seem to lack the poles. I'm not sure if this is a characteristic of the projection or if the data is simply missing. I've certainly seen maps made using the same data that don't have such large holes, but they may have filled some in with Venera or Pioneer data or something.
    Last edited by acrsome; 05-05-2014 at 09:51 AM.

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