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  • Positioning an image representing a geography


    In this article, you will learn how to position an image representing a geography over a Map Layer.

    This guide assumes you use the Map Chart in its default configuration (Coordinate Reference System (CRS): EPSG 3857 - WGS84).

    Your image represents the geography you want to position over a Map Layer. Before importing it, you need to know the geographical position and the size of your image on the map; this is called the ?Extent? and it is defined by the coordinates of the image anchor points on the map (Lat Max / Long Max, Lat Min / Long Min).

    image9_3.png.3dd700f463eff421d433e4a687891adc.png

    If your image already contains a geo-reference (.tiff, .geotiff...), you should follow the instructions described in the "Set position for a georeferenced image" section of this guide.

     

    Set position for a non-georeferenced image

    1. Open Spotfire, import your data and create a Map Chart visualization
      image6_5.png.3b40b8d1e8761c2fefc4ada3c3608bbc.png
       
    2. Zoom and pan to the area on the map where you want to position your image and right-click on the approximate Lat Max / Long Max location. The Map Chart contextual menu will appear.
    3. Click "Copy Map Coordinates" and paste the information into a text file.

      image5_5.png.f72cf99250ec994ee86f7aaff1dafae1.png
       
    4. Reproduce this for Lat Min / Long Min location
    5. Right-click the Map Chart visualization, select Properties, and go to the Layers section
    6. Select Add > Image Layer and click "Browse..." to select your image
    7. Open "Extent Settings..." and paste the anchor points information you saved previously:

      Lat Min / Long Min = Y low / X low

      Lat Max / Long Max = Y high / X high

      image4_4.png.33b0a931eb063c36bf094b7d43cf3db7.png
       
    8. If necessary, adjust the Extent Settings until you find the perfect position. It is important to enter the coordinates with as many decimal digits as possible to improve accuracy and avoid experimenting with positioning gaps and distortions.

      image7_4.png.d07516bc1e9eab6e2a732cad65854153.png

       

    Set position for a georeferenced image

    Some image formats (.tiff and .geotiff being the most popular) come with geographical extent information to make the positioning quicker and more accurate. Those images are often used for geological analysis and are generated using GIS software. You can use the same method as for non-georeferenced images to configure the Image Layer in Spotfire but we recommend getting the extent information directly from the image georeference in order to set the exact extent and avoid approximations and distortions.

    Using ESRI ArcGIS

    1. Open Spotfire, import your data and create a Map Chart visualization
    2. Add your image as an Image Layer and open its "Extent Settings..."
    3. Open ArcGIS and import your image as a Layer
    4. Open the Layer Properties in ArcGIS and got to the Source tab
    5. Copy and paste the anchor points information from ArcGIS to Spotfire:

      Bottom / Left = Y low / X low

      Top / Right = Y high / X high

      image2_7.png.e599cf9ffc94982079070e0fd397eca1.png

    Using QGIS

    1. Open Spotfire, import your data and create a Map Chart visualization
    2. Add your image as an Image Layer and open its "Extent Settings..."
    3. Open QGIS and import your image as a Raster Layer
    4. Open the Layer Properties in QGIS and go to the Information section
    5. Copy and paste the anchor points information from QGIS to Spotfire:

      1st value = Y high

      2nd value = X low

      3rd value = Y low

      4th value = X high

      image3_4.png.48322619899543904c0bec94231c7d5a.png

       

    Set the CRS of an image

    The Map Chart default Coordinate Reference System (CRS) is EPSG: 3857 - WGS84. If you need to use another CRS (EPSG: 4326 or else) proceed as follow:

    1. Right-click the Map Chart visualization, select Properties, and go to the Appearance section
    2. Set the Map Chart CRS to the desired CRS
    3. Add your Image Layer using the method described earlier
    4. Set the Image Layer CRS to the desired CRS

      image1_9.png.21f9d7fd8df0603d092239180db3ce86.png
       
    5. Go to the Layers section and remove the Map Layer (Map Chart cannot render the Map Layer in another CRS than default).

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