The Hierarchical Triangular Mesh
The Hierarchical Triangular Mesh
It is a ssumed you have either the Java htmIndex.jar or the C++ source and have sucessfully made teh binaries. To make the C++ get the tar file. Untar it. Then in the directory type :
./configure make make lookupIn the case of Java you have nothing to do.
You may get the latest available code from the download page.
The simplest application shipped with the HTM code is an ID lookup. In c++ this is a program called intersect. In java it is a clas called edu.jhu.htmExamples.lookup. Both applications work in the same manner taking a level to compute the id to and either an RA Dec or x,y,z coordinate. i.e.
In java :
java -classpath htmIndex.jar edu.jhu.htmExamples.lookup 20 45 45 (x,y,z) = 0.5000000000000001 0.5 0.7071067811865475 (ra,dec) = 45.0 45.0 ID/Name = 17557813719055 N333133333033333000033
In C++ :
lookup 20 45 45 Depth = 20 (x,y,z) = 0.5000000000000000, 0.5000000000000000, 0.7071067811865475 (ra,dec) = 45.0000000000000071, 44.9999999999999929 Lookup performance: 0.000000 /sec ID/Name = 17557813719055 N333133333033333000033
An online jsp page also provides a lookup service for RA,Dec at HtmTools.jsp
The real power of HTM lies in the convex intersections. The intersect application allows a "domain" file to be loaded and returns the HTMids which are contained in the domain. Domain files are described in the code files or you can look online at the javadocs for intersect .
The C++ application for perfomring an intersect is called "intersect" ant the equivolent java class is edu.jhu.htmExamples.intersect. Again both applications work in a similar manner. Most bassically you may pass a level and the name of a domain file.
Assume we have a simple domain file gr1 which defines a rectangle of 1 square degree as follows (this is in the src bundle) :
#DOMAIN 1 #RECTANGLE_RADEC 40.0 65.0 40.0 66.0 41.0 65.0 41.0 66.0
We may run this through intersect as follows.
In java :
java -classpath htmIndex.jar edu.jhu.htmExamples.intersect -symbolic 6 gr1 #DOMAIN 1 #CONVEX 4 ZERO -0.6427876096865396 0.7660444431189778 7.951790406489363E-16 0.0 ZERO -0.6891665347268039 -0.588603826377946 0.42260504372982827 0.0 ZERO 0.6946697916648571 0.5933040518358793 -0.40672371780292393 0.0 ZERO 0.656059028990507 -0.7547095802227723 7.95179040648939E-16 0.0 ZERO level is :10 olevel is :10 savelevel :5 nranges is :100 varlength :false expand :false Intersect took 34 milis N31331110000 N31331113333 N31331130200 N31331130200 N31331130202 N31331130203 N31331132100 N31331132133 N31331133100 N31331133103 N31331133121 N31331133121 N31331133130 N31331133133 N31333020121 N31333020121
In C++ :
intersect -verbose -symbolic 10 gr1 Depth = 10, output level = 10 #DOMAIN 1 #CONVEX 4 -0.64278760968654 0.7660444431189775 4.09237650802725e-16 0 -0.6891665347268034 -0.5886038263779464 0.4226050437298281 0 0.6946697916648575 0.5933040518358793 -0.4067237178029229 0 0.6560590289905068 -0.7547095802227725 2.822730285897355e-16 0 1 intersections done at a rate of inf intersections/sec N31331110000 N31331113333 N31331130200 N31331130200 N31331130202 N31331130203 N31331132100 N31331132133 N31331133100 N31331133103 N31331133121 N31331133121 N31331133130 N31331133133 N31333020121 N31333020121
Again the online jsp page provides an intersection service for triangles and rectangles at HtmTools.jsp
By default the list returned is the list of ranges of IDs contained in the domain. To get an exhaustive list add the -expand option. With -expand the above list would become the following list of 285 htms. As a sainty check consider that at level 10 there are 8,388,608 HTMs so in 1 sqaure degree we would expect to find ~ 203 htms in a square degree (41253 degrees on the sphere). Since the triangels will not fit exatly in a square degree we may assume more triangles than 203 will be returned.
N31331110000 N31331110001 N31331110002 N31331110003 N31331110010 N31331110011 N31331110012 N31331110013 N31331110020 N31331110021 N31331110022 N31331110023 N31331110030 N31331110031 N31331110032 N31331110033 N31331110100 N31331110101 N31331110102 N31331110103 N31331110110 N31331110111 N31331110112 N31331110113 N31331110120 N31331110121 N31331110122 N31331110123 N31331110130 N31331110131 N31331110132 N31331110133 N31331110200 N31331110201 N31331110202 N31331110203 N31331110210 N31331110211 N31331110212 N31331110213 N31331110220 N31331110221 N31331110222 N31331110223 N31331110230 N31331110231 N31331110232 N31331110233 N31331110300 N31331110301 N31331110302 N31331110303 N31331110310 N31331110311 N31331110312 N31331110313 N31331110320 N31331110321 N31331110322 N31331110323 N31331110330 N31331110331 N31331110332 N31331110333 N31331111000 N31331111001 N31331111002 N31331111003 N31331111010 N31331111011 N31331111012 N31331111013 N31331111020 N31331111021 N31331111022 N31331111023 N31331111030 N31331111031 N31331111032 N31331111033 N31331111100 N31331111101 N31331111102 N31331111103 N31331111110 N31331111111 N31331111112 N31331111113 N31331111120 N31331111121 N31331111122 N31331111123 N31331111130 N31331111131 N31331111132 N31331111133 N31331111200 N31331111201 N31331111202 N31331111203 N31331111210 N31331111211 N31331111212 N31331111213 N31331111220 N31331111221 N31331111222 N31331111223 N31331111230 N31331111231 N31331111232 N31331111233 N31331111300 N31331111301 N31331111302 N31331111303 N31331111310 N31331111311 N31331111312 N31331111313 N31331111320 N31331111321 N31331111322 N31331111323 N31331111330 N31331111331 N31331111332 N31331111333 N31331112000 N31331112001 N31331112002 N31331112003 N31331112010 N31331112011 N31331112012 N31331112013 N31331112020 N31331112021 N31331112022 N31331112023 N31331112030 N31331112031 N31331112032 N31331112033 N31331112100 N31331112101 N31331112102 N31331112103 N31331112110 N31331112111 N31331112112 N31331112113 N31331112120 N31331112121 N31331112122 N31331112123 N31331112130 N31331112131 N31331112132 N31331112133 N31331112200 N31331112201 N31331112202 N31331112203 N31331112210 N31331112211 N31331112212 N31331112213 N31331112220 N31331112221 N31331112222 N31331112223 N31331112230 N31331112231 N31331112232 N31331112233 N31331112300 N31331112301 N31331112302 N31331112303 N31331112310 N31331112311 N31331112312 N31331112313 N31331112320 N31331112321 N31331112322 N31331112323 N31331112330 N31331112331 N31331112332 N31331112333 N31331113000 N31331113001 N31331113002 N31331113003 N31331113010 N31331113011 N31331113012 N31331113013 N31331113020 N31331113021 N31331113022 N31331113023 N31331113030 N31331113031 N31331113032 N31331113033 N31331113100 N31331113101 N31331113102 N31331113103 N31331113110 N31331113111 N31331113112 N31331113113 N31331113120 N31331113121 N31331113122 N31331113123 N31331113130 N31331113131 N31331113132 N31331113133 N31331113200 N31331113201 N31331113202 N31331113203 N31331113210 N31331113211 N31331113212 N31331113213 N31331113220 N31331113221 N31331113222 N31331113223 N31331113230 N31331113231 N31331113232 N31331113233 N31331113300 N31331113301 N31331113302 N31331113303 N31331113310 N31331113311 N31331113312 N31331113313 N31331113320 N31331113321 N31331113322 N31331113323 N31331113330 N31331113331 N31331113332 N31331113333 N31331130200 N31331130202 N31331130203 N31331132100 N31331132101 N31331132102 N31331132103 N31331132110 N31331132111 N31331132112 N31331132113 N31331132120 N31331132121 N31331132122 N31331132123 N31331132130 N31331132131 N31331132132 N31331132133 N31331133100 N31331133101 N31331133102 N31331133103 N31331133121 N31331133130 N31331133131 N31331133132 N31331133133 N31333020121
