5.3.4 Re-georeference image - LUPMISManual

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5. Conversion of data > 5.3 Raster maps

5.3.4 Re-georeference Image

Level of expertise required for this Chapter: Beginner; general Map Maker training

If you detect a misplacement of the image (orthophoto) displayed at Map Maker, in comparison with your GPS-tracked locations, you are recommend to adjust the georectification of the image:

1. If the image is in ECW format, you have to convert it to JPG format by: Map Maker > Main menu > Bitmap utilities > Convert file format > from ECW > Choose file window: Select folder and file > Open > Save as window: Select file type: JPG, folder, specify filename > Save > Select calibration option window: No calibration > OK

(You have to do this conversion, because most graphics programs can not read ecw files. ecw format is very fast to display in GIS, has reasonably small file sizes, hardly any loss of information due to compression, and with in-built georeference).

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2. In the graphics program (e.g. Paint Shop Pro): Open the image (previously converted to JPG format) > Select the frame of interest, which might be half or third or even less > Image > Crop to Selection > File > Save As window: Select file type: JPG, select folder, specify file name according to following file naming convention:


Geographic reference (e.g..easting/northing)

Type or date

_

Projection

Example:

328082

col

_

utm

328082W

col

_

utm


The compression factor should be low (around 20-25 with low compression, very good quality)

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3. In Map Maker, you calibrate the newly created image with the procedure, as explained above: Main menu > Utilities > Bitmap utilities > Calibrate scan > Two known points > Choose file window: Select file type: JPG, folder and file. (See also Chapter 5.2.3 for full description). Choose two points, which can be clearly identified both on the image and by the GPS tracking, and write down their coordinates prior to calibration. Then, save as new file.

Check in Map Maker, that the new image has a better georeference.


  


 
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