Project 1811 gdal_question 02 - geopaparazzi/Spatialite-Tasks-with-Sql-Scripts GitHub Wiki

2. Can I used gdal_rasterize to draw shape over the GeoTIFF with transparency

yes, you can use 'gdal_rasterize'
- together with 'gdalbuildvrt' and 'gdal_translate'

Goal:

create an png image
- which is a combination of the pgn-image created in 'Question 3'

QGIS :

a rasterized image of the streets of 1786 (in green - 0,173,83)
a rasterized image of the streets of 1844 (in red - 255,0,0)

With the exception of the given colour, the commands are the same:

gdal_rasterize -tr 0.475211759942328 0.475212956422887 -te 24800 20700 25800 21300 -ot Byte -init 192 -a_nodata 192 -burn 0 -burn 173 -burn 83 -sql "SELECT ST_Buffer(soldner_segment,2.5) FROM segments_berlin_1786" ../sources/berlin_segments_qgis.db segments_berlin_1786_green.tif

Parameters:

Use of the following parameters only for new images

-a_nodata, -a_srs, -co, -init, -of, -ot, -tap, -te, -tr and -ts

For creation of new image only:

-a_nodata
- 192
  - read value from gdalinfo
-te: [ulx (min_x) lry (min_y) lrx (max_x) uly (max_y)]
- 24800,20700,25800,21300
  - --projwin [ulx (min_x) uly (max_y) lrx (max_x) lry (min_y)]
    - 24800 21300 25800 20700
      - do not get confused at the different order between -te and projwin
-tr (xres yres)
- 0.475211759942328 0.475212956422887
  - use the resolution found in the final png-image with gdalinfo
    - Pixel Size = (0.475211759942328,-0.475212956422887)
      - Note: the yres must be a positive value
-init: Pre-initialize the output image bands
- 192
-ot: for an RGB Image
- Byte

For creation of both new image and existing image:

-burn the RGB values desired
- green (dark) : 0,173,83
  - -burn 0 -burn 173 -burn 83
- red : 255,0,0
-sql
- this is needed for 2 reasons:
  - the used view has more than one field/column
    - using -l with the view-name returns a blank image
    - thus SELECT soldner_segment FROM segments_berlin_1786
      - soldner_segment will be used
        
        Warning: this will cause the created line to be 1 pixel wide
  - ST_Buffer(): this will set the width of the created line
    - sample found here: 'Controlling output linewidth linestyle using gdal_rasterize shapefile shp to Geotiff'
    - to calculate the value used with ST_Buffer:
      - linestring width 5.0 (pixels)
      - image resolution 1.0 (pixels per meter)
        
        2.5=((1*5)/2)
      - image resolution 970.429903115999991 (pixels per meter)
        
        2426.07475779=((970.429903115999991*5)/2)
  - the final sql used was
    - SELECT ST_Buffer(soldner_segment,2.5) FROM segments_berlin_1786
ogr-source
- in this case I used a spatialite database
output-file

Note:

the combination of -init and -ot seem to insure that the created image is an RGB image
- and thus show up correctly in QGIS (otherwise the lines are black, Grayscale)

Next step: combine the 3 images with:

'gdalbuildvrt'
- first create a file with a list of the input-images
  - 1811.Neuester_Grundriss_von_Berlin.streets.txt
  - for use with the -input_file_list parameter

1811.Neuester_Grundriss_von_Berlin.5800.3068.area_rote_rathausturm_panorama.png
segments_berlin_1844_red.tif
segments_berlin_1786_green.tif

Note:

the order is important
- that that comes last, wins (i.e. will be shown)
  - in this case I want the 'younger/red/1844' streets
    - to be over-painted by the 'older/green/1786' streets
      - both should over-paint the map

gdalbuildvrt -overwrite -b 1 -b 2 -b 3 -resolution highest -vrtnodata '192' -input_file_list 1811.Neuester_Grundriss_von_Berlin.streets.txt 1811.Neuester_Grundriss_von_Berlin.streets.vrt
# create the final png, after checking the .vrt file in QGIS
gdal_translate -of PNG  1811.Neuester_Grundriss_von_Berlin.streets.vrt 1811.Neuester_Grundriss_von_Berlin.streets.3068.png

The final result of 1811.Neuester_Grundriss_von_Berlin.streets.3068.png:

PNG :

All roads lead to Rome

this is one, of possibly, many

--> 'Answer to question 3: Can I read a part of the GeoTIFF using GDALRasterIO and write as PNG with the same transparency preserved.'

<-- 'Answer to question 1: Can I create a transparent GeoTIFF like PNG with alpha channel ?'

<-- 'Question of 2015-06-10 from gdal-dev'

2015-06-11: Mark Johnson, Berlin Germany