GPS-iPaq Workshop

by

Verplanke / de BieITC

Version Feb ‘03

Mobile GIS techniques with 10m accuracy !!

GPS-iPaq Hardware Parts

Pocket PC The Compaq-iPAQ pocket PC (64 MB Ram), running at > 200 Mhz under MS-Windows-CE) is able to run ArcPad and to connect to a GPS.

The Pocket PC has backlight-features so that in bright sun the screen is still perfectly readable.

Arc-Pad Arc-Pad is able to convert GPS readings ‘on-the-fly’ to the required coordinate system.

Any image, GT-Sheet, or shapefile can be displayed in Arc-Pad ‘as is’. The GPS position is shown on the loaded maps or images.

The user can save the GPS-Tracklog (as lat-long points), or use the GPS to capture shapefiles (point, line, or polygon) in the required projection system.

The software allows use of forms (questionnaires), and to draw points, lines, or polygons directly by hand on the screen.

Raster images must be converted to SID files using Erdas (v.8.5).

Arc-Pad software comes with an extension that loads into Arc-View or Arc-Map.

Some relevant info …

Example-1 … Pakistan

1881m2

1038m2

RMS boundary

Digitized line of GT-Road and Circular-Road

PeshawarCity

Points of Interest

ForestGISOffice

2 Fields:

Part of GT-Sheet

ArcPad Menu

Scale: 1:65540

DHV guesthouse

Digitized “on the road”

Scanned topsheet

Jan. 2000

Sep. 2002

Sep. 2002

Example-2 … India

IRS-Image (23m Multi-spectral fused with 6m Pan)

Digitized “in the field”

Example-3 … Iran

Jul. 2001

Aster-Image(15m Multi-spectral) Digitized “in

the field” and “on the road”

Aster-Image, Topsheet, GPS

data…All fit !!!

Connecting Hardware-1

USB hub

Power

Connecting Hardware-2

GPS physical connectionA GPS serial connector wire needs to be linked to a serial connector wire attached to the iPaq. Both ends are female and need to be connected through a null-modem connector in which pins 2 and 3 are reversed (home made…).

Connecting Hardware-2

GPS physical connectionA GPS serial connector wire needs to be linked to a serial connector wire attached to the iPaq. Both ends are female and need to be connected through a null-modem connector in which pins 2 and 3 are reversed (home made…).

Connecting Hardware-2

Connection precautionWhile cycling, walking or running, the connections must remain firmly in place. Use tape to provide the required solid ‘fix’.

Connecting Hardware-2

Power

Watch your battery lifeOn the road, a cigarette-lighter wire provides recharge options for the iPaq.Use rechargeable A4 batteries for the GPS. Carry spares with you at all times.

USB hub

• Activesync use your CD will establish the required ‘communication’

Software installation-1

Software installation-2

• Arcpad on your PC run:

Software installation-3

USB hub

• Arcpad from your PC to your iPaq install from [Start] - [ArcPad]

Hardware settings: GPS

GPS settings

• units’ settings: position format: hddd.dddddo, map datum: WGS 84, and units: metric

• ‘interface’ settings: i/o format: NMEA out, and baud rate: 4800.

Hardware settings: ArcPad

Arc-Pad settings

• GPS: NMEA protocal, WGS84 Datum

• GPS Port: port com1, Baud 4800, Parity none, Data bits 8, Stop bits 1, Break 0.

To convert ‘on-the-fly’ coordinates send by the GPS to Arc-Pad, at least one Arc-View shapefile must be loaded as Arc-Pad layer for which a projection file (*.prj) exists in the same directory as from where the shapefile was loaded.

Example “Enschede” :

PROJCS["ED_1950_UTM_Zone_32N",GEOGCS["GCS_European_1950",DATUM["D_European_1950",SPHEROID["International_1924",6378388,297]],PRIMEM["Greenwich",0],UNIT["Degree",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["False_Easting",500000],PARAMETER["False_Northing",0],PARAMETER["Central_Meridian",9],PARAMETER["Scale_Factor",0.9996],PARAMETER["Latitude_Of_Origin",0],UNIT["Meter",1]]

Projection settings-1

Then, when applicable, the correct datum shift must be selected within ArcPad.

Example “Enschede” :

Projection settings-2

Prepare projection file-1

Select in ArcView a shapefile and start the “ArcView Projection Utility”.

ArcPad 6 supported projections:

• Geodetic coords. (Lat-Long)

• Alberts Equal Area Conic

• Cylindrical Equal Area

• (Double) Stereographic

• UTM (TM; Gauss-Kruger)

• Lambert Conformal Conic

• New Zeeland National Grid

Prepare projection file-2

Start in ArcMap the “ArcPad Tools” wizard and export a *.SID image.

Images can be compressed by a factor 25!!! No need is left to prepare clumsy JPG's for ArcPad. MrSID images will do!! They hardly suffer from resolution loss when compressed, and can cover substantial areas ( the original IMG file must be < 50 MB).

Example: an AP from Enschede is compressed from 25 to 1 MB. Shown is a fraction of the original image!!

SID IMG

Compress Images

Performance in Hills

Often, main roads are poorly mapped on GT-sheets, while (15m resolution) images of mountainous areas hardly show the roads.

Digitizing roads by GPS in hills proved very useful and accurate enough to fill this shortcoming.

Digitizing administrative boundaries in hills on foot using a GPS is not considered practical.

Roads digitized in Ghazi RMS on top of a GT sheet and on an Aster image (Febr.2001; scale 1:25,000).

Mapping in the Field-1

Mapping in the Field-2

Performance under trees

Cycling to work during a cloudy morning provided the yellow line.

It is projected on AP’s, an Ikonos image and the Top-10 of Enschede.

Where high trees were present, tracking with the GPS give visible errors.

ArcPad can provide accuracy warnings !!!

Mapping in the Field-3

Part of an old GT sheet and the new feeder canal under construction at Tarbela on a recent Aster image (Febr.2001); scale 1:25000.

Use of GPS to check Image Geo-Referencing quality

Outdated GT-Sheets can create problems while georeferencing images.

Through the GPS-Ipaq set, digitized roads can be used to check if images are properly geo-referenced.

The geo-referencing of the Aster image (Febr.’01) is clearly not matching required standards.

GPS-iPaq Warnings

• Not for GIS amateurs

• Requires user to know facts on projection systems ‘properly’

• Requires proper preparation:

• of geo-referencing images

• of compressing images

• of converting shapefiles

• of preparing symbologies

• of preparing forms

• Requires proper GPS-ArcPad software settings

Once all is done well….experience shows too many advantages and

even a dependancy of

using the equipment during

fieldwork !!!

The ArcPad

manual is only 390 pages

thick !!!

GPS-iPaq Hardware Parts

Hardware Alternative/future

Trimble's GeoXM™ GPS CE handheld, from the GeoExplorer® CE series, combines a Trimble GPS receiver and a powerful Windows CE operating system into one rugged unit. The result is a convenient and versatile handheld that's perfect for mobile GIS applications.

Prices starting at $2895. -

0.72 kg with battery7 hrs battery lifeUSB connectivity128 MB Flash data storage2–5 meter accuracy

Try-out files for Enschede