04 May 2006 1

Map Server and Client09 May 2006

Joseph Czechowski IV (TMA)Jay Hallam (Zeta)

04 May 2006 2

What Is It?NeXtEarth consists of two components:

Map server•Serves images in a GoogleEarth-like manner

from an NGA data set

Client•Can be any system that meets the API

•NeXtMidas PLOT command is one such client

04 May 2006 3

Why?Using a map server versus accessing the NGA data set directly means:

Requires fewer sites to be updated with new data setsEasier to build clients, simpler API Clients can run anywhere, not just where direct access (via NFS) is practical

• Can now use WebStart

Available on any networkClient is platform-independent

Windows, Linux,…

Integrated into NeXtMidasNatively supports Midas files as overlays

04 May 2006 4

APIAPI based on GoogleMaps’ API

Each view is made up of N tiles• Each tile is a 256x256 pixel JPEG

Tiles are “stitched” together by client when drawn to screenNumber of tiles requested by client depends on screen resolution/size• Example (screen is 1024 x 768):

1024256

768256

+1 X +1 = 24

04 May 2006 5

API (Cont.)

Examples:GoogleMaps:• http://<server>/kh?t=tq&v=3• Modified Mercator Projection

NeXtEarth:• http://<server>/nms?t=tq&background=bluemarble• LatLon/Equirectangular Projection

– Same as used by NGA, XGEOPLOT

04 May 2006 6

API (Cont.)

API based on GoogleMaps’ APIPositioning and resolution determined by QuadTree algorithm• 1st Resolution Level = t

– (whole world in one 256x256 JPEG)

• 2nd Resolution Level = tq, tr, ts, tt– (whole world takes four 256x256 JPEGs)

• Nth Resolution Level (N > 2)– (whole world takes 8x4(N-3) 256x256 JPEGs)

tq

tt

tr

ts

04 May 2006 7

API (Cont.)1st Resolution Level

(whole world in one 256x256 JPEG)

Algorithm assumes 180 for both latitude and longitude so that:

• Causes black bar at the top/bottom in levels 1 and 2. • After 2nd zoom level there is no data above 90oN or below

90oS

Below 90o S

Above 90o N

DegLatPixel

DegLonPixel

=

t

04 May 2006 8

API (Cont.)

2nd Resolution Level(whole world takes four 256x256 JPEGs)

Below 90o S

Above 90o N

tq

tt

tr

ts

04 May 2006 9

API (Cont.)

3rd Resolution Level(Whole world takes eight 256x256 JPEGs)

ttq ttr tsq tsr

tqt tqt trt trt

04 May 2006 10

API (Cont.)

4th Resolution Level(Whole world takes 32 JPEGs)

tqtr

tqts

tqtq

tqtt

04 May 2006 11

API (Cont.)

Known API DifferencesMap Projection (from server)• Google uses a modified Mercator projection,

NeXtEarth uses LatLon (matches NGA data)

v= argument vs. options=• Google indicates plot options with v=[integer]• NeXtEarth uses options=[string]

– Example: options=ALLIMAGERY+JOG+ONC

04 May 2006 12

API (Cont.)

Known API Differences (cont)Background = option• NeXtEarth allows control over the “background”

(low-resolution image), many users use BLUEMARBLE or NONE

Hybrid maps in Google• Imagery with streets overlaid option in Google

04 May 2006 13

DevelopmentClient-server approach was a natural progression from existing NeXtMidas functionality

Used existing rendering in PLOT•Made data available over HTTP

Based client on existing NeXtMidas client for GoogleMaps

Basic functionality and first site installation required only two weeks of work

Approximately 1000 lines of new code

04 May 2006 14

Development (Cont.)

NGA Data

NGA Data

InMemoryImage

Plot

PlotJPEG JPEG

Render Draw

Render DrawNetwork

Stand-Alone NeXtMidas (Geoplot):

NeXtEarth:

Connecting to GoogleMaps:

PlotJPEGDraw

NetworkGoogle

04 May 2006 15

Server Installation

Requires JavaOptionally C compiler (MrSID)

Server installation steps:Install NeXtMidasInstall MAP option treeRun MAPPER to create MTOC

Starting the server:Run MAPSERVER primitive• See explain file for list of options

04 May 2006 16

Future Considerations

Add support for Google Keyhole Markup Language (KML) files

XML files defining map overlays and features

Serve up XML files defining available data

Indicates available chart types and coverage mesh

Ability to get data from a remote database