GeoMesa Utils¶

Useful utilities are found in the geomesa-utils module.

Simple Feature Wrapper Generation¶

Tools can generate wrapper classes for simple feature types defined in TypeSafe Config files. Your config files should be under src/main/resources. Add the following snippet to your pom, specifying the package you would like the generated class to reside in:

<build>
    ...
    <plugins>
        ...
        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <version>1.3.2</version>
            <executions>
                <execution>
                    <id>generate-sft-wrappers</id>
                    <phase>generate-sources</phase>
                    <goals>
                        <goal>java</goal>
                    </goals>
                    <configuration>
                        <mainClass>org.locationtech.geomesa.utils.geotools.GenerateFeatureWrappers</mainClass>
                        <cleanupDaemonThreads>false</cleanupDaemonThreads>
                        <killAfter>-1</killAfter>
                        <arguments>
                            <argument>${project.basedir}</argument>
                            <argument>org.foo.mypackage</argument>
                        </arguments>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

Geohash¶

Geohashes are a geocoding system that uses a Z-order curve to hierarchically subdivide the latitude/longitude grid into progressively smaller bins. The length of a Geohash in bits indicates its precision.

For example, the table below shows Geohash bounding boxes around the point (-78.48, 38.03) with increasing levels of precision in units of bits (the coordinates are rounded to three decimal places for clarity):

bits	bounding box	centroid	geohash
1	-180.000 -90.000, 0.000 90.000	-90.000 0.000	0
2	-180.000 0.000, 0.000 90.000	-90.000 45.000	01
3	-90.000 0.000, 0.000 90.000	-45.000 45.000	011
4	-90.000 0.000, 0.000 45.000	-45.000 22.500	0110
5	-90.000 0.000, -45.000 45.000	-67.500 22.500	01100
6	-90.000 22.500, -45.000 45.000	-67.500 33.750	011001
7	-90.000 22.500, -67.500 45.000	-78.750 33.750	0110010
8	-90.000 33.750, -67.500 45.000	-78.750 39.375	01100101
9	-78.750 33.750, -67.500 45.000	-73.125 39.375	011001011
10	-78.750 33.750, -67.500 39.375	-73.125 36.563	0110010110
11	-78.750 33.750, -73.125 39.375	-75.938 36.563	01100101100
12	-78.750 36.563, -73.125 39.375	-75.938 37.969	011001011001
13	-78.750 36.563, -75.938 39.375	-77.344 37.969	0110010110010
14	-78.750 37.969, -75.938 39.375	-77.344 38.672	01100101100101
15	-78.750 37.969, -77.344 39.375	-78.047 38.672	011001011001010
16	-78.750 37.969, -77.344 38.672	-78.047 38.320	0110010110010100
17	-78.750 37.969, -78.047 38.672	-78.398 38.320	01100101100101000
18	-78.750 37.969, -78.047 38.320	-78.398 38.145	011001011001010000
19	-78.750 37.969, -78.398 38.320	-78.574 38.145	0110010110010100000
20	-78.750 37.969, -78.398 38.145	-78.574 38.057	01100101100101000000
21	-78.574 37.969, -78.398 38.145	-78.486 38.057	011001011001010000001
22	-78.574 37.969, -78.398 38.057	-78.486 38.013	0110010110010100000010
23	-78.486 37.969, -78.398 38.057	-78.442 38.013	01100101100101000000101
24	-78.486 38.013, -78.398 38.057	-78.442 38.035	011001011001010000001011
25	-78.486 38.013, -78.442 38.057	-78.464 38.035	0110010110010100000010110

The bounding boxes corresponding to the Geohashes in the table above are shown as red polygons on this map:

The org.locationtech.geomesa.utils.geohash.GeoHash class provides tools for working with Geohashes. The data for the table above may be generated with the following Scala code:

import org.locationtech.geomesa.utils.geohash.GeoHash

for (p <- 1 to 25) {
  val gh = GeoHash(-78.48, 38.03, p)
  println(s"""$p ${gh.bbox.toText} ${gh.getPoint.toText} ${gh.toBinaryString}""")
}

Base-32 Encoding¶

Geohashes are encoded as strings with the following base-32 representation:

dec	binary	base-32	dec	binary	base-32
0	00000	0	16	10000	h
1	00001	1	17	10001	j
2	00010	2	18	10010	k
3	00011	3	19	10011	m
4	00100	4	20	10100	n
5	00101	5	21	10101	p
6	00110	6	22	10110	q
7	00111	7	23	10111	r
8	01000	8	24	11000	s
9	01001	9	25	11001	t
10	01010	b	26	11010	u
11	01011	c	27	11011	v
12	01100	d	28	11100	w
13	01101	e	29	11101	x
14	01110	f	30	11110	y
15	01111	g	31	11111	z

By this convention, the 25-bit Geohash that contains (-78.48, 38.03) described above would be encoded as “dqb0q”:

01100 10110 01010 00000 10110
----- ----- ----- ----- -----
  d     q     b     0     q