Mike and Nicolas,

Thanks for taking the time to explain all of this to me, it did clear up some misunderstandings I had.


best regards,
John

On 8/30/2016 12:54 PM, Michael Treglia wrote:
Hey John,

I've dealt with this layer a bit too - one thing for QGIS is that when you import a layer, I think the default to calculate the min/max based on the 2-98% range of the data. If you're in the Layer Properties -> Style tab, expand the 'Load min/max values' area, and then select 'Min / max' (and change Accuracy to 'Actual'), and then hit the load button. That yields the range as 207-15516. (see screen-shot below). I know this is a categorical raster, so displaying based on the color ramp is meaningless, but that at least shows you're getting the right values.

Re the projection - I thought this used to display correctly based on the projection parameters that get read in, but it's displaying way far north. Toying around, it looks like the equivalent EPSG code is 5070 (+proj=aea +lat_1=29.5 +lat_2=45.5 +lat_0=23 +lon_0=-96 +x_0=0 +y_0=0 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs)

FWIW, I did this on QGIS 2.16.1

Hope that helps,
mike


Inline image 1

On Tue, Aug 30, 2016 at 12:23 PM, Nicolas Cadieux <nicolas.cadi...@archeotec.ca <mailto:nicolas.cadi...@archeotec.ca>> wrote:

    Hi,
    The easy answer is no:(

    That could happen If the nature of the file was different (like a
    simple picture .jpg) but in this case, as in most, you have
    choices to make and assumptions are made by the programs based
    partly on the user settings. The problem is that most rasters used
    in GIS have more than the usual 256 values you find in a picture.
    Therefore, you need to select what part of the image you want to
    display or render on the screen which is limited to 256 values only.

    As an example, you can ask QGIS to automatically open a raster
    using the min-max pixel or you can ask Qgis to cut off the higher
    and lower 1%. (Also, min max values can be real (slow) or
    estimated (fast)). The second option may be better if you know you
    have noise in the data.  To have a true idea of what the real min
    max values are, you need to run the statistics. You can't rely on
    rendering values shown under the layers.

    The problem you are having with the CRS is probably that ArcGis or
    ERDAS, is coding the information differently than in Qgis. Some
    software companies do it differently either because they want to
    lock you in a proprietary format or because they think their
    format is better.    If I recall, ERDAS does not put the
    information in the .tiff but rather, in a text file.  (I may be
    wrong here.)  In any case, look an compare the CRS definitions.
    They maybe identical.  You can also click on the layer and specify
    the CRS. If you want to change the CRS, you will need to use the
    save as option.

    ArcGIS also has a concepts of dealing with rasters that have
    unique values.  The idea, is that you can have a raster with a
    data base.  After that, pixels with the value of 1, for example,
    could be identified as "Roads". That concept does not exist in
    Qgis (as of 2.12).  You can however, make a colour palette for the
    unique values but Qgis will not id the values as objects like
    roads or building.  I imagine this will come soon if it's not
    already in 2.16.

    Unfortunately, all those choices used for rendering get saved in
    the project files and while most GIS will open a great number of
    file formats correctly, most are completely incapable of reading
    each other's project files:(. If they can, they have very limited
    options.

    Hope this clarifies things a bit.
    Nicolas


    Envoyé de mon iPad

    Le 30 août 2016 à 11:24, john.polo [via OSGeo.org
    <http://osgeo.org>] <[hidden email]
    <http:///user/SendEmail.jtp?type=node&node=5283092&i=0>> a écrit :

    Hi,
    I downloaded the raster at this site:
    http://www.wildlifedepartment.com/facts_maps/ecoregions.htm
    <http://www.wildlifedepartment.com/facts_maps/ecoregions.htm>
    (scroll down about halfway to find the raster link. The file is
    kind of
    big, ArcGIS says the uncompressed size is 5.69 GB, 225 MB as a zip)
    and loaded it into QGIS as a standalone raster file. It is a
    raster of
    Oklahoma, USA classified into vegetation types at 10mx10m
    resolution.

    It is saved as ERDAS Imagine, if I understand the extension. I don't
    know if the file type is relevant to the issues I am running into.

    When the file is open in QGIS, the min and max pixel values have a
    smaller range, 314 - 14797, than when the file is open in ArcGIS,
    207 -
    15516. I can redraw the raster in ArcGIS to "Unique" instead of
    "Stretched" pixel values in the Symbology, which will then give me
    classifications for the pixels. Additionally, the CRS is
    USER:100002 in
    QGIS, but Albers Conical Equal Area in QGIS. Why does this
    difference in
    rendering happen? How can I get QGIS to render the file with the
    same
    characteristics as ArcGIS automatically? I know I can save with a
    new
    CRS to fix that issue, but if the file can load in ArcGIS with
    the CRS
    from the start, shouldn't QGIS render it the same? I don't know
    how to
    get the pixel values to the same range or how to get the
    classifications
    assigned.

    John

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