osmodel

README

osmodel

Images on this page contains OS data © Crown Copyright (2021), used under the Open Government License

osmodel is a command-line application which uses the other packages in this repository to generate different representations of the supported OS OpenData. datasets.

It has 3 subcommands:

• surface: Generate a "surface" from a specified region of an elevation dataset, e.g. as a CSV file.
• texture: Generate an image from a specified region of a raster dataset.
• mesh: Generate a 3D model, optionally with a texture, from a specified region of elevation and raster datasets. e.g. as an STL or X3D file, suitable for 3D printing.

Getting started

Make sure you have go installed, any recent version should work (1.14+ maybe?)

Build/install

Either:

• Clone this repository
• cd osgrid/cmd/osmodel
• go get .
• go build .
• Run ./osmodel

Or:

• Run go install -v github.com/usedbytes/osgrid/cmd/osmodel@master
• Run osmodel, assuming your go binary directory is on your $PATH

Get some data

Go to OS OpenData. and download some data.

For elevation data, get Terrain 50, "ASCII Grid".

For raster data, I've used OS VectorMap District, "GeoTIFF Full Colour" successfully.

Extract each of the zip files into their own directory and point the --elevation and/or --raster flags to those directories, which should contain a folder called data.

surface subcommand

The surface subcommand just outputs elevation data, using the terrain50 package.

It can output to different text-based formats, like .csv, .tsv, and also has a .dat output (just space-separated data) which is suitable for use with OpenSCAD's surface() command. Note however, that for 3D modelling applications, the mesh command below is a better option.

It can also output to a greyscale PNG image (ligher color --> higher elevation), also usable with OpenSCAD's surface() command.

The --srgb flag applies the sRGB transfer function to image outputs, making them better for "viewing", but useless for use as a data format, because the values become non-linear.

By default (except for image formats), the surface data is exported South -> North, so the first row of values represents the Southern-most part of the region. This can be changed with the --flip option.

The --hres option allows setting a (lower) resolution for the elevation data, which is useful for reducing the number of data points for exporting large areas.

The OSMODEL_ELEVATION_DB environment variable can be set to the elevation data directory, or it can be passed as the --elevation argument

Example usage:

Output a viewable PNG representing a 5 km * 5 km area around Cheddar Gorge

./osmodel surface --elevation ~/data/terrain50 --srgb -w 5000 -o cheddar.png ST 46697 53996

texture subcommand

The texture subcommand outputs raster images, using the raster package.

The OSMODEL_RASTER_DB environment variable can be set to the raster data directory, or it can be passed as the --raster argument

Example usage:

Output a 3 km area around the centre of Cambridge

./osmodel texture --raster ~/data/vectormap -w 3000 -o cambridge.png TL 45201 58287

Known issue:

Note that this impacts the Cambridge example above!

The golang.org/x/image/tiff package which is used for decoding the TIFF images has an issue where it throws "unexpected EOF" for some images. For example tile NO08 exhibits this problem.

I've posted a patch which appears to fix it: https://github.com/golang/go/issues/30827#issuecomment-774469551

I probably should either make a vendored version of that module and pin it in this package, or try out a different TIFF decoder package.

mesh subcommand

The mesh subcommand is the primary purpose of this repository - it can generate 3D models suitable for 3D printing.

It supports writing to STL and X3D files, as well as generating OpenSCAD polyhedron() code (though the files end up being quite big!).

The --hscale/-H and --vscale/-V flags allow you to set a scale for horizontal and vertical directions respectively; by default they are set to give 1 cm per km horizontally, and 2 cm per km vertically, assuming the output files units are 1 mm.

In the case of X3D, it can also generate a "texture" from raster data and apply it to the mesh, these can then be printed in full colour on an appropriate machine - I have done this successfully using Shapeways' full colour sandstone.

Example usage:

Generate a textured X3D model of the area around Snowdon's summit:

./osmodel mesh --elevation ~/data/terrain50 --raster ~/data/vectormap --texture -V 1:100 -o snowdon.x3d

Aligning with "other" imagery

The OS OpenData. raster datasets are great, but real aerial imagery is even better.

I haven't found a freely/easily available source of aerial imagery to integrate directly with this tool.

However, if permitted by the terms of service of any of the free online mapping sites with aerial imagery, it would be theoretically possible to generate a texture image using --texture, manually line that up with a screenshot of some aerial imagery, and replace the texture image file.

I am not a lawyer, but my reading of Bing's Print Rights would allow this for personal use.

Here is a textured model of the area around Bowness-on-Windermere made using this technique.

Aerial imagery courtesy of Bing Maps, Earthstar Geographics SIO, (C) Microsoft 2022