This page introduces how to merge several tiles into one, which is then easier to stylize, and to treat (shaded relief). It also introduces how to create shaded relief through Gdaldem hillshade or the QGis Shaded relief plugin, and the associated GIMP whitening to improve this relief.
Formerly, most GIS raster layers were provided through many small tiles to download separately (lighter to download), then to merge together on your computer. However, since 2011, the new NASA downloading system :
take advantage of higher bandwidth and allow the downloading of one heavy tile of the wished size, for ETOPO, SRTM3, Aster, etc.
Many small tiles to merge (depreciated)
|
---|
Merge layers is based on their nature : vector or raster. This later ease later application of color style, layer management, and files/project sharing. For raster such as topographic data (SRTM, ETOPO, etc.), shaded relief, natural earth skin, ... use :
|
To merge vectors layers there is a similar pathway from QGis (1.6) > Vector. However, vector being light, it is usually not necessary to merge them
Last, for vector to merge with raster, vector layers can be converted to raster before to be merged with raster base map, and for raster with vector, raster base map can be converted to vector to be merged with vector layers.
According to
this recent post and its comments :
or
It is necessary to enter a number as a "z factor". "z factor" may be 1 or a big number, like 10000 or 100000, in order to make a better relief. So, you have to try different numbers as "z factor". Unfortunately, flat zones won't be transparent, but thanks to z-factor flat zones will be almost insignificant, while shades of mountains will be enough appreciable.
Example for SRTM90, for a zone about 100x100km. Choose z=75000, and 315° azimuth / 75° altitude. Name this layer shaded relief, and in the properties of this layer > transparency > choose band 1 and set the global transparency to approx. 60%.
No more need to editing the file with GIMP ! (or maybe only for a less-weight file, png to jpg for example)
If you really want a full transparency in flat zones, you must use The Gimp after any of these methods. See below.
On Ubuntu, the install of QGis *seems* to also install Gdaldem hillshape. Its command is:
$ cd /my/folder/with/my_GIS_files/inside/ $ gdaldem hillshade input_dem.ext output_hillshade.ext -z 5 -s 111120 -az 315 -alt 60
The following specific options are available :
-z
zFactor:
-s
scale:
az
azimuth:
-alt
altitude:
Then, load into QGis, apply an opacity of 30%, and it will look great. ; )
Generate shaded reliefs from QGis, its "Shaded relief" plugin, and SRTM or other topographic files is very easy. So:
But the final Print Composer output quality depends of the size of your output.
The operation can be applied to a serie of SRTM .tif files by selecting the containing folder.
We can optimize the shaded relief in a bitmap editor, either TheGIMP (free), or Photoshop (proprietary). The tutorials below display TheGIMP, but reading them will also help a lot if you plan to use Photoshop. The shaded relief and topographic data production are natively strongly oriented toward technical application, sciences, accuracy, and thus towards extreme details. On the other side, the purpose and needs of making maps for Wikipedia and our general public push us to be human friendly, and thus look for graphical lightness and elegance. Thus, out of the 4 operations below: one operation increases the visible details, while the three others make the information load smaller by reducing details so that the endresult will be more human friendly and... outrageously elegant.
Concept: Reinforcing contrast, especially shadows. Duplicate the shaded relief layer, make a pixel operation : multiply. Darkest pixels get darker (multiply). while brightest ones almost don't change. (Increase reability).
In this way you reinforce the density of the shadows resulting from this main illumination. Next usual step: see #Whitening.
Complement, progress: 0%. Waiting for descritpion of method. Looking for an editor! Concept: Combine shaded reliefs with different sunlight orientation to avoid blind spot. You will merge 3 shaded relief layers with 315⁰ (NW sunlight, default layer), +355⁰ layer, +275⁰ sunlights, respectively. (Increase details, accuracy)
Concept: Combine a lower precision reliefs (use lower sources or blur it) with a hight quality one, so the major feature appears more compare to the usual overload of small details. ("Avoid chartjunk/overload").
Also to try out: GIMP > Filters > Map > Map bumping
Concept: make the shaded relief whiter, or better transparent, so only the shadows appear. Make lighter background ("Avoid
chartjunk/overload").
Specifics: Work on RGB files only. When opening the .tif file in GIMP, the landmass appear grey, northwest sides of hills appear white, while hills' south east side (shadow) appear black. With some programs (gdaldem hillshade), water bodies also appear black, creating confusing and difficulties for the graphist. We want to make white-softgrey (and black waters bodies -only-) transparents. We want to keep the darkgrey-black reliefs.
You risk to also delete black shadows. You may prefer to simply later and conveniently hide black water by one of the widely available water's vector layers.
The table above has links to various tutorials and resources which can help in the creation of Wikipedia maps from digital georeferenced data ( GIS).
This page introduces how to merge several tiles into one, which is then easier to stylize, and to treat (shaded relief). It also introduces how to create shaded relief through Gdaldem hillshade or the QGis Shaded relief plugin, and the associated GIMP whitening to improve this relief.
Formerly, most GIS raster layers were provided through many small tiles to download separately (lighter to download), then to merge together on your computer. However, since 2011, the new NASA downloading system :
take advantage of higher bandwidth and allow the downloading of one heavy tile of the wished size, for ETOPO, SRTM3, Aster, etc.
Many small tiles to merge (depreciated)
|
---|
Merge layers is based on their nature : vector or raster. This later ease later application of color style, layer management, and files/project sharing. For raster such as topographic data (SRTM, ETOPO, etc.), shaded relief, natural earth skin, ... use :
|
To merge vectors layers there is a similar pathway from QGis (1.6) > Vector. However, vector being light, it is usually not necessary to merge them
Last, for vector to merge with raster, vector layers can be converted to raster before to be merged with raster base map, and for raster with vector, raster base map can be converted to vector to be merged with vector layers.
According to
this recent post and its comments :
or
It is necessary to enter a number as a "z factor". "z factor" may be 1 or a big number, like 10000 or 100000, in order to make a better relief. So, you have to try different numbers as "z factor". Unfortunately, flat zones won't be transparent, but thanks to z-factor flat zones will be almost insignificant, while shades of mountains will be enough appreciable.
Example for SRTM90, for a zone about 100x100km. Choose z=75000, and 315° azimuth / 75° altitude. Name this layer shaded relief, and in the properties of this layer > transparency > choose band 1 and set the global transparency to approx. 60%.
No more need to editing the file with GIMP ! (or maybe only for a less-weight file, png to jpg for example)
If you really want a full transparency in flat zones, you must use The Gimp after any of these methods. See below.
On Ubuntu, the install of QGis *seems* to also install Gdaldem hillshape. Its command is:
$ cd /my/folder/with/my_GIS_files/inside/ $ gdaldem hillshade input_dem.ext output_hillshade.ext -z 5 -s 111120 -az 315 -alt 60
The following specific options are available :
-z
zFactor:
-s
scale:
az
azimuth:
-alt
altitude:
Then, load into QGis, apply an opacity of 30%, and it will look great. ; )
Generate shaded reliefs from QGis, its "Shaded relief" plugin, and SRTM or other topographic files is very easy. So:
But the final Print Composer output quality depends of the size of your output.
The operation can be applied to a serie of SRTM .tif files by selecting the containing folder.
We can optimize the shaded relief in a bitmap editor, either TheGIMP (free), or Photoshop (proprietary). The tutorials below display TheGIMP, but reading them will also help a lot if you plan to use Photoshop. The shaded relief and topographic data production are natively strongly oriented toward technical application, sciences, accuracy, and thus towards extreme details. On the other side, the purpose and needs of making maps for Wikipedia and our general public push us to be human friendly, and thus look for graphical lightness and elegance. Thus, out of the 4 operations below: one operation increases the visible details, while the three others make the information load smaller by reducing details so that the endresult will be more human friendly and... outrageously elegant.
Concept: Reinforcing contrast, especially shadows. Duplicate the shaded relief layer, make a pixel operation : multiply. Darkest pixels get darker (multiply). while brightest ones almost don't change. (Increase reability).
In this way you reinforce the density of the shadows resulting from this main illumination. Next usual step: see #Whitening.
Complement, progress: 0%. Waiting for descritpion of method. Looking for an editor! Concept: Combine shaded reliefs with different sunlight orientation to avoid blind spot. You will merge 3 shaded relief layers with 315⁰ (NW sunlight, default layer), +355⁰ layer, +275⁰ sunlights, respectively. (Increase details, accuracy)
Concept: Combine a lower precision reliefs (use lower sources or blur it) with a hight quality one, so the major feature appears more compare to the usual overload of small details. ("Avoid chartjunk/overload").
Also to try out: GIMP > Filters > Map > Map bumping
Concept: make the shaded relief whiter, or better transparent, so only the shadows appear. Make lighter background ("Avoid
chartjunk/overload").
Specifics: Work on RGB files only. When opening the .tif file in GIMP, the landmass appear grey, northwest sides of hills appear white, while hills' south east side (shadow) appear black. With some programs (gdaldem hillshade), water bodies also appear black, creating confusing and difficulties for the graphist. We want to make white-softgrey (and black waters bodies -only-) transparents. We want to keep the darkgrey-black reliefs.
You risk to also delete black shadows. You may prefer to simply later and conveniently hide black water by one of the widely available water's vector layers.
The table above has links to various tutorials and resources which can help in the creation of Wikipedia maps from digital georeferenced data ( GIS).