mihir3445 / laz-perf

Alternative LAZ implementation for C++ and JavaScript

What is this?

LAZperf is an alternative LAZ implementation. It supports compilation to WASM via Emscripten so that LAZ data can be decoded in a browser.

Building LAZperf for Windows/UNIX

Previous versions of LAZperf were header-only C++ libraries, so you could simply include the project header files in your project. Primarily due to licensing issues, this is no longer the case and LAZperf needs to be built as a library that links with your code. LAZperf uses CMake as a build system, though it's probably simple to port to another build system as there are few source files and no dependencies. Assuming you have Git, CMake, make and C++11 compiler installed, here is the process on the Unix command line. The process is similar on Windows.

git clone https://github.com/hobu/laz-perf.git
cd laz-perf
mkdir build
cd build
cmake ..
make

This should build the library liblazperf.so (or similar). You can install this library along with the supporting header files as follows:

make install

Using LAZperf on Windows/UNIX

Although the LAZperf library is focused on decoding the LAZ data itself, there is support for reading a complete LAS or LAZ file. If you have LAZ-comrpessed data, you can decompress by creating a decompressor for the right point type and providing a callback that will provide data from the LAZ source as requested by the decompressor. For example, to read point format 0 data, you might do the following:

using namespace lazperf;

void cb(unsigned char *buf, int len)
{
    static unsigned char my_laz_data[] = {...};
    static int idx = 0;

    std::copy(buf, buf + len, my_laz_data + idx);
    idx += len;
}

point_decompressor_0 decompressor(cb);

char pointbuf[100];
for (int i = 0; i < num_points; ++i)
    decompressor(pointbuf);

Compression follows a similar pattern -- see the accompanying examples and tests.

You can also use LAZperf to read LAZ data from an entire LAZ or LAS file:

using namespace lazperf;

reader::named_file f(filename);

char pointbuf[100];
for (size_t i = 0; i < f.header().point_count; ++i)
    c.readPoint(pointbuf);

A memory file interface exists If your LAS/LAZ data is internal rather than in a file:

using namespace lazperf;

reader::mem_file f(buf, bufsize);

char pointbuf[100];
for (size_t i = 0; i < f.header().point_count; ++i)
    c.readPoint(pointbuf);

Buiding LAZperf for use in a browser.

In order to build LAZperf for the browser, you must have the Emscripten SDK installed. You will also need Git and CMake. Activate the installation to set the necessary EMSDK environment variable then follow these steps:

git clone https://github.com/hobu/laz-perf.git
cd laz-perf
mkdir build
cd build
. ../emscripten-build.sh

This should create two files in the subdirectory build/cpp/emscripten: laz-perf.js and laz-perf.wasm. Both are necessary for running LAZperf from the browser.

Using LAZperf in a browser

See the file cpp/emscripten/index.html for an example of how to decode LAZ data in the browser. Note that laz-perf.js will fetch laz-perf.wasm when run. You don't need to fetch it manually.