Mapping Vietnam

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This is about building a web mapserver to share maps of Vietnam

Obtain source maps

If you already know the numbers of the maps you need,

  1. Go to USGS site http://store.usgs.gov/
  2. Click Advanced Search
  3. Enter map number in Old Material
  4. Click "Search"
  5. Click on the map image
  6. Save the PDF file

Samples for testing

  • 1501ANC4810
  • 1501ANC4811
  • 1501ANC4815

You can also use the search features to find what you need.

Working with GeoPDFs

The GeoPDFs downloaded from USGS were scanned from paper maps, converted to a digital form (probably TIFF) and then georeferenced. Then they were converted to GeoPDF format using TerraGo Publisher.

Each scan covers only a relatively small area on the ground. So to create a complete seamless map for use on the web, we must

  1. Convert GeoPDFs to some format that we can further process.
  2. Remove the collars (the border containing legend, dates, etc).
  3. Process the set of resultant files into tiles that can be served.

Step one: Reading GeoPDF

If you are using ArcMap you can use "TerraGo Publisher for ArcGIS" ($2700) to import GeoPDFs directly. At this point, you can treat the GeoPDF data as you would any other ArcMap data source. Unfortunately $2700 is outside my budget.

Another excellent commercial product is Global Mapper (retails for $349). It can read the PDFs and export them as GeoTIFFs. An added plus, it has code to remove the collars and can also reproject the files if needed. I am told it is scriptable too.

You could ignore the geospatial encoding in the source PDFs and convert them into a format (TIFF for example) readable by ArcMap and then georeference it, but that's a lot of work given the PDF is already georeferenced!

The very latest version of GDAL (1.8.0) can read GeoPDFs. It's free and I have worked with it in the past, so I am giving it a try.

Recipe to convert a GeoPDF to a GeoTIFF using GDAL

% gdal_translate -of GTiff -co "TILED=YES" -co "TFW=YES" 1501ANC4815_geo.pdf 1501ANC4815_geo.tif

This generated a 47 MB TIFF that is 4470 x 3375 pixels.

You can learn more about GeoTIFF options here: http://www.gdal.org/frmt_gtiff.html A good one to use might be "-co "COMPRESS=LZW"

Step two: Removing collar

With (the Windows program) Global Mapper this is as simple as checking an option box for the layer. But it's a Windows-only program.

  1. Use gdalinfo to read the header to find the location of the collar.
  2. Use a script to find the corners (there can be many points defining the edges but I only want the corners)
  3. Convert the raster to a GCS using gdalwarp
  4. Convert the extracted corners to GCS using gdaltransform.
  5. Remove the collar using gdal_translate

Note that it is also possible to simply trim away using trial and error, for example, 

% gdal_translate -srcwin 350 0 4120 2750 -of GTiff -co "TILED=YES" 1501ANC4815_geo.pdf 1501ANC4815_geo.tif

1 Detect collar using gdalinfo

According to the "Acrobat Supplement to the ISO 32000" there is a definition in the file to tell me where the map lives. The gdalinfo command reveals the NEATLINE setting: 

NEATLINE=POLYGON ((
445035.80158801417565  999277.556482305750251,  ul
444993.235997625160962 991902.349403560161591,
444864.738057852664497 884201.712978136376478,  ll
452159.580137342331    884208.817744017927907,
585964.54743435990531  884289.527591207530349,
614300.221590773784555 884383.269830735283904,  lr
614190.235319046885706 999293.477391553344205,  ur
605175.140901734353974 999218.552309990860522,
553978.789515793323517 999300.979716640315019,
505958.457250406034291 999353.427943945163861,
451172.635888226970565 999382.750743734533899,
445035.722449889173731 999360.237513555795886,
445035.80158801417565  999277.556482305750251,
445035.80158801417565  999277.556482305750251,
445035.80158801417565  999277.556482305750251))

The corners of the image with collar included are given as: 

Corner Coordinates:
Upper Left  (  429999.053,  999725.915) (104d21'46.72"E,  9d 2'39.27"N)
Lower Left  (  430135.804,  856853.093) (104d21'58.76"E,  7d45' 6.78"N)
Upper Right (  619287.590,  999910.271) (106d 5' 7.80"E,  9d 2'41.48"N)
Lower Right (  619424.341,  857037.449) (106d 4'59.36"E,  7d45' 9.52"N)
Center      (  524711.697,  928381.682) (105d13'28.20"E,  8d23'57.68"N)

The corners correspond to the edges of the "paper". To visualize things, I put the neatline points and the corners into a text file, then loaded the map TIFF into QGIS, and used the "Add delimited text file" plugin to add the text file to the map. The points all fell onto the neatline.

2 Find the corners

I wrote a little Python to sort them. It looks like this. 

#!/usr/bin/env python

import math

neatline = [
 (445035.80158801417565,  999277.556482305750251),
 (444993.235997625160962, 991902.349403560161591),
 (444864.738057852664497, 884201.712978136376478),
 (452159.580137342331,    884208.817744017927907),
 (585964.54743435990531,  884289.527591207530349),
 (614300.221590773784555, 884383.269830735283904),
 (614190.235319046885706, 999293.477391553344205),
 (605175.140901734353974, 999218.552309990860522),
 (553978.789515793323517, 999300.979716640315019),
 (505958.457250406034291, 999353.427943945163861),
 (451172.635888226970565, 999382.750743734533899),
 (445035.722449889173731, 999360.237513555795886),
 (445035.80158801417565,  999277.556482305750251),
 (445035.80158801417565,  999277.556482305750251),
 (445035.80158801417565,  999277.556482305750251) ]

UpperLeft  =(  429999.053,  999725.915) #(104d21'46.72"E,  9d 2'39.27"N)
LowerLeft  =(  430135.804,  856853.093) #(104d21'58.76"E,  7d45' 6.78"N)
UpperRight =(  619287.590,  999910.271) #(106d 5' 7.80"E,  9d 2'41.48"N)
LowerRight =(  619424.341,  857037.449) #(106d 4'59.36"E,  7d45' 9.52"N)

Size = (4470, 3375)

ul = neatline[0]
ur = neatline[0]
ll = neatline[0]
lr = neatline[0]

def dist(p1, p2):
    dx = math.pow(p2[0] - p1[0], 2)
    dy = math.pow(p2[1] - p1[1], 2)
    return math.sqrt(dx + dy)

def closer(corner, p1, p2):
    if dist(corner, p1) < dist(corner, p2):
        return p1
    return p2

for n in neatline:
    ul = closer(UpperLeft, ul, n)
    ur = closer(UpperRight, ur, n)
    ll = closer(LowerLeft, ll, n)
    lr = closer(LowerRight, lr, n)

fp = open("/home/bwilson/Downloads/nl.csv", "w")
fp.write("x, y\n")
fp.write("%f, %f\n" % ul)
fp.write("%f, %f\n" % ur)
fp.write("%f, %f\n" % ll)
fp.write("%f, %f\n" % lr)
fp.close()

It generates a file containing the neatline corners, which looks like this 

x, y
445035.722450, 999360.237514
614190.235319, 999293.477392
444864.738058, 884201.712978
614300.221591, 884383.269831

3 Reproject the raster

Conveniently this command converts it from GeoPDF to a GeoTIFF at the same time. 

gdalwarp -t_srs EPSG:4326 1501ANC4810_geo.pdf -of GTiff 1501ANC4810_4326.tif

4 Convert the extracted corners to GCS using gdaltransform

gdaltransform command 

gdaltransform -s_srs EPSG:3148 -t_srs EPSG:4326 < nl.csv
104.496065478207 9.04334959786241 -12.9164893552661
106.035159775414 9.04163128037419 -24.1458563385531
104.495875664344 8.00173981131893 -17.4262739224359
106.033366794208 8.0023968002259 -28.6638822425157

5 Remove the collar using gdal_translate

Using map coords (using data from map): -projwin ulx uly lrx lry 

% gdal_translate -projwin 445035.722450 999360.237514 614300.221591 884383.269831 -of GTiff -co "TILED=YES" 1501ANC4815_geo.pdf 1501ANC4815_geo.tif

Step three: make tiles

Turning one TIFF into a map 

% gdal2tiles.py -t Vietnam -g ABQIAAAAGRHc9gAG3W9UhaqQD0pvExSVvaIHsSWhBu9dnlvZR7nHQNV82hT1HFUt0HcccsqJ2Z2e8femz7wrsw -u http://wildsong.biz/map/ 1501ANC4811_4326.tif vietnam

This creates a set of PNG files and HTML files in the output directory "vietnam". I then copy them up to the server and you can see them at http://wilkdsong.biz/map/vietnam

But I want to have multiple input files. I can merge them and then tile the output file. I also want to zoom in more than allowed by default so I make more zoom levels. 

% export GKEY="ABQIAAAAGRHc9gAG3W9UhaqQD0pvExSVvaIHsSWhBu9dnlvZR7nHQNV82hT1HFUt0HcccsqJ2Z2e8femz7wrsw"
% export URL="http://wildsong.biz/map/"
% gdal_merge.py -o vietnam.tif -of GTiff 1501ANC4810_4326.tif 1501ANC4811_4326.tif 1501ANC4815_4326.tif'
% gdal2tiles.py -t "Vietnam" -g $GKEY -u $URL -z 7-14 vietnam.tif vietnam

More data

Additional map layers from ESRI: http://www.arcgis.com/home/group.html?q=tags:ArcMap931_Base&t=group&owner=esri&title=ESRI%20Maps%20and%20Data&sortField=title&sortOrder=asc&content=all

Notes

GeoPDF is a trademark of TerraGo. The generic term is "geospatial pdf". Please in your mind translate all references to GeoPDF in this document to "geospatial pdf". Thank you.

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