stitching_etopos
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stitching_etopos [2023/07/08 13:51] – bushwalking | stitching_etopos [2023/08/31 08:55] (current) – Add link bushwalking | ||
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I recently went to considerable effort to stitch together NSW 1:25k e-Topo (PDF) maps into one big raster, for use in OziExplorer. I figured it would be worthwhile to document the steps, with a bit of background. The same process may be useful for stitching other georeferenced maps with collars. | I recently went to considerable effort to stitch together NSW 1:25k e-Topo (PDF) maps into one big raster, for use in OziExplorer. I figured it would be worthwhile to document the steps, with a bit of background. The same process may be useful for stitching other georeferenced maps with collars. | ||
+ | |||
+ | Note that it is skewed towards Windows users, and assumes a certain level of technical knowledge (eg running commands on the command line), and that you have GDAL installed and the path to the binaries in your PATH. | ||
+ | |||
+ | The following answer from GIS Stack Exchange has more details on resampling and compression options: | ||
+ | https:// | ||
===== 0. Background on UTM and map dimensions ===== | ===== 0. Background on UTM and map dimensions ===== | ||
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===== 1. Download eTopos ===== | ===== 1. Download eTopos ===== | ||
+ | These can be downloaded from [[https:// | ||
While there is a 5 map per day limit, this can be naughtily bypassed by grabbing a copy of the {{ : | While there is a 5 map per day limit, this can be naughtily bypassed by grabbing a copy of the {{ : | ||
While you're there, also grab the {{ : | While you're there, also grab the {{ : | ||
+ | |||
+ | There is also a [[https:// | ||
===== 2. Remove borders ===== | ===== 2. Remove borders ===== | ||
Once you have the PDFs, the next step is to strip off the border of the PDF and convert to a raster format. We can do this for a single image using gdalwarp, by setting a few options, including: | Once you have the PDFs, the next step is to strip off the border of the PDF and convert to a raster format. We can do this for a single image using gdalwarp, by setting a few options, including: | ||
- | * -t_srs <target spatial reference> | + | * -t_srs <target spatial reference> |
* -r < | * -r < | ||
* -cutline - applies a mask to the raster (confusingly, | * -cutline - applies a mask to the raster (confusingly, | ||
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* -crop_to_cutline - crops to the mask applied under " | * -crop_to_cutline - crops to the mask applied under " | ||
* -dstalpha - sets an output alpha band so that the pixels that are outside the cutline but inside the bounding box are transparent. This is needed when merging in the next step | * -dstalpha - sets an output alpha band so that the pixels that are outside the cutline but inside the bounding box are transparent. This is needed when merging in the next step | ||
+ | * -co COMPRESS=LZW (optional) - will reduce the size of the intermediate GeoTiffs | ||
Sample command in full - you'll need to set your own directories, | Sample command in full - you'll need to set your own directories, | ||
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The GeoTiff file can be used as is in many applications. | The GeoTiff file can be used as is in many applications. | ||
+ | |||
+ | There are other compression options ('' | ||
+ | |||
+ | The '' | ||
===== 5. Create OZFX4 file for OziExplorer ===== | ===== 5. Create OZFX4 file for OziExplorer ===== | ||
- | For OziExplorer, | + | For OziExplorer, |
stitching_etopos.1688788276.txt.gz · Last modified: 2023/07/08 13:51 by bushwalking