aprs is a registered trademark bob bruninga, wb4apr copyright © 2003 – john beadles, n5oom all...

APRS is a registered trademark Bob Bruninga, WB4APR

Copyright © 2003 – John Beadles, N5OOMAll Rights Reserved

Maps for APRS

John Beadles, N5OOM



Purpose of this Presentation

• This presentation is an introduction to the topic of digital map data

• I’m still working on this presentation, so it’s a little scattered and there are some holes

• This topic is waaay too big to be contained in a 1 hour presentation

• But hopefully this will get you started!

• If you want to know precisely how to get maps into your APRS software, you need to refer to the documentation for your application



Topics

In this presentation, we will cover:

• Types of digital maps

• Coordinates

• Types of Maps

– Vector Maps

– Raster Maps

• Map types used by various APRS Software

• Map Products useable for APRS

• Links to Online Resources



Types of Digital Maps

• Feature maps

– Roads, political boundaries, utilities, hydrology, digital elevations, etc.

– Constructed from ground surveys, aerial and satellite photos

– Often one feature type per map data file (or “layer”)

• Geoid Models

– Gravitational field map, used for high precision surveying, etc.

– Constructed by using aerial, satellite gravity surveys

• Digital Elevation Models

– Model of the shape of the earth

– Used for RF propagation modelling, construction estimation, flood plain modelling

– Constructed by ground surveys, stereo aerial photo digitization, SARsat mapping

• For the purposes of



Coordinates

• Digital maps may use either of two types of coordinates

– Latitude / Longitude

– Plane Coordinates

• Usually we’ll use Latitude and Longitude



Latitude and Longitude

• Latitude and Longitude (lats and lons) is a spherical coordinate system that is intended to uniquely locate points on a round earth

• Latitude is expressed as an angle from the equator.

– Latitude is zero at the equator, 90 degrees at the poles

– Lats in the northern hemisphere are expressed as positive or “north” value. Lats in the southern hemisphere are expressed as negative or “south”.

– Example: +32.5000 or 32.5 degrees North

• Longitude is expressed as an angle from an imaginary line (the prime meridian) running through Greenwich, England

– Longitude is zero at the prime meridian and 180 degrees on the opposite side of the earth

– Lons east of the prime meridian are positive or “east”, west of the prime peridian are negative or “west”

– Example: -90.70 degrees or 90.70 degrees west.



Lats & Lons on the EarthLatitudes and Longitudes are angles created from artificial mathematical constructs that we use to describe the shape of the earth.

Any given point on the earth will have a different latitude and longitude depending on where we say the center of the earth is, how the axes are rotated and where we say the prime meridian is.

The set of parameters that list this information is called a DATUM. There are many different datums that have been used for specific purposes. The Lat and Lon for a place on the earth in one datum may not be the same in another datum.

The datum that is used by the U.S. Navstar GPS system is WGS-84, which is practically interchangable with NAD-83

+ 0 to 180 Degrees

Longitude

- 0 to 180 Degrees

Longitude

Degrees Latitude

Degrees

Longitude

+ 0

to

90

De

gre

es

La

titu

de

- 0

to

90

De

gre

es

La

titu

de

The Prime Meridian is a linethat runs from pole to pole

through Greenwich, England. Itis the line from which Longitude

is measured.

Latitude is measuredfrom the equator, withthe equator being at 0

degrees.



Lat / Lon Conversions

• For convenience sake, lats and lons may be expressed many different ways.

• Decimal degrees is a common expression

– Example: 32.5250, -97.3250

• APRS uses degrees and decimal minutes

– Example: 32 31.50N, 97 19.50W

– Convenient because a minute of angle is roughly 1 nautical mile

– Decimal degrees = dd + mm/60

– DD MM.mm = Int(DecDeg) and (mod(DecDeg))*60

• Degrees, Minutes, Seconds is used to subdivide degrees down

– Example: 32d 31m 30s N, 97d 19m 30s W

– Decimal degrees = dd + mm/60 +ss/3600



Datums

• As we said, latitude and longitude are angles that are used to identify unique locations on the world

• But the lat and lon coordinate construct is a pure mathematical construct that doesn’t have any particular relationship with the real world

• A datum is a set of definitions that tell us how lat and lon relate to the real world. A datum defines the shape for the earth (the ellipsoid), the origin of the coordinate system with respect to the center of the earth and rotation vectors that describe how the coordinate system origin matches to physical locations.

• There are many datums that have been constructed to deal with many local mapping issues. This happened a lot when computing power was expensive or non-existent. With the advent of cheap computers and GPS, the number of datums will probably narrow down, but there are many historical datums out there.

• Latitudes and Longitudes in one datum will not be equal to those in another, and the difference isn’t necessarily constant



Coordinate Conversion

• Sometimes you might get map data in coordinates other than Lat / Lon or you might have to convert Lat / Lon from one datum to another

• Corpscon

– is a free MS Windows based conversion tool from the US Army Corps of Engineers

– http://crunch.tec.army.mil/software/corpscon/corpscon.html

• Blue Marble Geographics

– Industry standard tools, but expensive

– http://www.bluemarblegeo.com/

• Gpsinformation.net

– Has references to a lot of GPS data download tools

– http://gpsinformation.net/

• Other times you might have to modify the format of GPS data to get it into a map.

– Often you can open GPS data files with a text editor (notepad, etc.)

– Some modification can be done with a spreadsheet

– For more extensive changes, the Perl language is a very powerful tool for doing data processing

– www.perl.org for www.activestate.com for MS Windows ports



Datums for APRS

• Generally speaking, american users will only be interested in a few.

• The Navstar GPS system uses WGS-84 (World Geodetic System of 1984) as its’ native system. The accepted civil datum for the United States is NAD-83 (North American Datum of 1983), which almost identical to WGS-84.

• WGS-72 and WGS-64 were earlier attempts at a global datum. Neither are in common use.

• NAD-27 (North American Datum of 1927) is a very old regional datum. This datum was defined by long distance surveys across the entire United States. Accumulated error in the surveys resulted in a very non-linear expression of Lats and Lons across the U.S.

• Other countries use other datums

• The higher the resolution your maps, the more important it is that your GPS is set to the same datum as your maps. The difference can be thousands of meters.

• I can keep going on this subject for an hour alone, so we’re going to drop it here.



Types of Maps

• Vector Maps

• Raster Maps



Vector Map Characteristics

• A vector map is a file of raw data that a computer uses to draw a map on demand

• Lines and other objects are defined as coordinate pairs

• Maps with unformatted text can be pretty ugly

• Map features can be dynamically edited

• Sometimes used with associated database entries (Geographic Information Systems)

• Includes Tiger data, USGS DLG data used with some APRS software

BEGIN LINE

32.744033,-96.894967

32.744033,-96.894833

32.743967,-96.894767

32.743933,-96.894767

32.743883,-96.894767

32.743817,-96.894767

32.743700,-96.894700

32.743567,-96.894617

32.743417,-96.894567

32.743250,-96.894517

32.743100,-96.894483

32.743000,-96.894417

32.742983,-96.894300

END



• Is basically a picture

• Accompanied with a file containing associated geographic information

• Features are drawn on and cannot be easily modified

• Often used as a base map on which other features are drawn

• .GIFs, .JPGs, GeoTiffs

• Is the default map type used by UI-View, can be used with Xastir, WinAPRS

096.47.216W,34.05.628N

096.46.154W,34.04.781N

2003 MS-150 Sun Lunch Stop

Raster Maps



Raster Map Example



Map products useable for APRS



Vector Data

• Census Dept TIGER Data

– Xastir

• USGS Digital Line Graphs

• WinAPRS / MacAPRS file format

– WinAPRS / MacAPRS

– UI-View

– Xastir

• PocketAPRS file format

• Commercial Data

– Used in MapInfo, AutoCad

– Would need to be converted to proper format

• Tiger data is complete, but quality can be highly variable but is updated regularly

• USGS DLG (Digital Line Graphs) are digitized versions of USGS 1:24000 maps, rarely updated

• Commercial data is often Tiger data that is formatted and cleaned up – very expensive!

• Some conversion software exists to convert TIGER, DLG data to WinAPRS / MacAPRS format



Consumer Software Products

• Delorme StreetAtlas

– APRS+SA

– UI-View (some versions of SA)

• Precision Mapping

– UI-View

– WinAPRS

• Microsoft MapPoint

– APRSPoint

• Generally APRS software that uses a consumer product doesn’t directly access the data directly, it uses a programming interface to talk to the mapping software, which does what the APRS software wants it to do

• Therefore, the APRS program is dependent on the programming interfaces provided by the map software. Not all map software provides this interface.

• Map data used in consumer map products is virtually always proprietary – you aren’t allowed to access or convert the raw data.

• Most of these products are based on updated TIGER data from the US Census Dept.



Web Based Products

• APRSWorld

• Tiger Map Server

• MapBlast

– JavAPRS

– Radio Mobile

• TerraServer

– UI-Terra

– Xastir

• Used to create a raster map which you can then take with you

• Can’t make new maps unless you are connected to the internet

• UI-Terra is downloadable from the UI-View web site

• Radio Mobile is an RF Propagation package that can be used to make APRS (UI-View) compatible raster maps



Scanned & Raster Maps

• GeoTIFFs

– Various sources

– WinAPRS / MacAPRS

– Xastir

• Digital Raster Graphics

• UI-View map format

– Graphic image & geoinfo file

• GeoTiffs are a specific image format that has associated geographic information associated with it

• Digital Raster Graphics are scanned copies of USGS 1:24000 maps

• UI-View format is a .bmp or .jpg with an associated text file containing the lats and longs of the upper left and lower right corners.



GIS Data

• Arcinfo Shape Files

– Xastir

• MapInfo

– Useable only after conversion

• GIS data is generally vector data that is formatted for a particular industrial GIS application

• ArcInfo shape files are useable by some applications

• Need to check copyright information on the source data.



Do It Yourself Data

• May be needed to correct bad map data

• Collect with GPS

– Use within a mapping program (such as a “draw layer” in StreetAtlas

– Or save as a text file and compile into a vector format useable directly by a program

• Hand drawn

– Street Atlas provides a function for drawing roads in by map



Manipulating data files

• If you have a GPS data file from some where, and it won’t import, try opening it up in a text file.

• If the file isn’t full of binary data, save a clean copy and then see what happens when you modify the files



Map File Formats

• GeoTiffs

• Xastir Pixmaps

• UI-View Image Files

• Street Atlas Draw Files



GeoTIFF• A GeoTIFF file is a TIFF image file with geographic information imbedded in the image

– The geographic image data file may be buried in the TIFF image file

– Or may be in a separate .FGD file

• They are a standard in the GIS industry

• However, TIFFs are generally high-resolution images and aren’t compressed, so they tend to be very large

• Sometimes they are available commercially

– Such as these canadian quad maps

– http://www.softmaptech.com/en/pages/geotiff_EN.html

• Othertimes through government or public works sites

Minimum contents of a sample .FGD file

1.5.1.1 WEST BOUNDING COORDINATE: -122.000000

1.5.1.2 EAST BOUNDING COORDINATE: -120.000000

1.5.1.3 NORTH BOUNDING COORDINATE: 48.000000

1.5.1.4 SOUTH BOUNDING COORDINATE: 47.000000

Taken from: http://www.xastir.org/manual/sec_mapdetails.html



Xastir Pix Map

• Consists of two files

– A pixel map (.xpm)

– A geographic calibration file (.geo)

Sample .geo file

FILENAME world1.xpm

# x y lon lat

TIEPOINT 0 0 -180 90

TIEPOINT 639 319 180 -90

IMAGESIZE 640 320

Sample .geo file

FILENAME world1.xpm

# x y lon lat

TIEPOINT 0 0 -180 90

TIEPOINT 639 319 180 -90

IMAGESIZE 640 320

.geo files can have many elements:

FILENAME filename

This specifies the filename of a map image to be loaded from the local disk.

URL http://website

This specifies the URL of a map image to be loaded from a web or ftp site. ImageMagick only.

TIEPOINT x-pixel y-pixel longitude latitude

Two tiepoints are required, and more than 2 will be ignored. these two lines are for connecting an x,y pixel position in the image to a lat and long position on the earth. The points should be as close as possible to the upper left corner and the lower right corner of the image for best accuracy.

IMAGESIZE pixels horizontally pixels vertically

This specifies the size of the image in pixels. If this is not set, the image will be loaded each map redraw, regardless if it is on screen or not.

DATUM datum

This feature is not implemented.

PROJECTION projection

This feature is only partially implemented, default is "LatLon", other possibility is "TM" to specify that the map is in Transverse Mercator projection.

# anything Any line with the first character of a '#' will be ignored.

Taken from: http://www.xastir.org/manual/sec_mapdetails.html



UI-View Maps (from UI-Terra)

Sample .inf file

096.47.216W,34.05.628N

096.46.154W,34.04.781N

2003 MS-150 Sun Lunch Stop

UI-Terra builds an area photo by downloading photo tiles from TerraServer and generates a text .inf file containing the upper left and lower right coordinates of the image.

The name that shows up in UI-Views’ Maps list



UI-View Maps (from RadioMobile)This map is a combination of a digital terrain map and a mapblast road map. This map was exported with a UI-View .inf geographic information file.

Had we wished to do so, we could have left the terrain map blank so we would just see the streets.



Street Atlas Draw Files• Draw files allow Street Atlas users a way to

draw and save their own features in Street Atlas

• Each file consists of one or more files bounded by a “BEGIN” and “END” keyword.

• Each pair of coordinates represents a vertex in a line segment.

• Features include

– LINE

– HILITE (I think)

– POINT (I think)

• StreetAtlas draw files are easy to manipulate, but gps data may be out of order in the file

• This causes straight lines to be drawn across your map

Sample StreetAtlas Draw File

BEGIN LINE

33.259445,-96.680179

33.259649,-96.679974

33.261023,-96.679923

33.264370,-96.679897

33.265486,-96.679897

33.270593,-96.679770

33.274906,-96.679693

END

BEGIN LINE

33.275828,-96.679693

33.275785,-96.670428

33.275785,-96.664037

33.276579,-96.663242

33.278596,-96.663062

33.278403,-96.658340

33.278446,-96.656492

33.278446,-96.654438

33.278435,-96.652313

END



More to come…

I’m still working on this slide package. More file formats are coming eventually!



UI-View Maps used during the Dallas White Rock Marathon

A UI-View map created in MapInfo. Used manually edited GPS data, and a UI-View overlay (.pos) file for display.

Each feature is loaded as a separate data set and manually tuned for the best appearance.

The .inf geographic reference file was created by manually mousing to the upper left and lower right corners of the window and converting the coordinates with a calculator.



Links to Online Resources

• US Census Dept

– http://www.census.gov

• US Geological Survey

– http://geography.usgs.gov

• National Geodetic Survey

– http://www.ngs.noaa.gov

• Navtech Seminars

– http://www.navtechgps.com

• National Imagery and Mapping Agency

– http://www.nima.mil

• Radio Mobile

– http://www.cplus.org/rmw/english1.html

• UI-View Map tools

– http://www.ui-view.com/uiview32/mapsoftware.shtml

Useful books from Navtech Seminars:

“Glossary of Mapping, Charting and Geodetic Terms”

Defense Mapping Agency

“Geodetic Glossary”

National Geodetic Survey, Rockville, MD

“NOAA Professional Paper NOS 2, North American Datum of 1983”

National Geodetic Survey, Rockville, MD

“Map Projections – A Working Manual”

U. S. Geological Survey professional paper; 1395



More presentations in this series available at:

http://www.n5oom.org/2004_hamcom/presentations.htm

aprs is a registered trademark bob bruninga, wb4apr copyright © 2003 – john beadles, n5oom all...

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