GEO 265
Introduction to Digitizing

Digitizing

A way of RETRACING your map

Going from analog to digital

Your digitizing PUCK or CURSOR...
EMITS an electrical or light signal when you push one of its buttons

Your digitizing TABLET...
has conductors or sensors that RECEIVE the signal from the puck and convert these to relative tablet positions

Major form of inputting data to a GIS

Takes your map and literally makes it digitial - captures geographic coordinates

Class Notes, pages 19-38

Go into Arc/INFO, turn on digitizer, and run DIGTEST command

digtest 9100 com1:9600:8bit

Definitions: ARC, NODE, VERTEX, etc.

More Definitions

WEED Tolerance - sets minimum distance between VERTICES when digitizing - weeds out vertices within this tolerance or distance

SNAP Distance - sets minimum distance between NODES before their locations are snapped together to coincide

Map Preparation

Map should be in good condition and with reliable information

We will use paper but mylar is best because it doesnt shrink or warp

Mark begin/end point on donut polygons

Mark label points in centers of polygons

Mark nodes every 3-4 in. on longer curvy lines - makes correcting errors easier

Mark clearly and number TICS

Digitizing

Mount map on digitizer with tape
Start ADS program in Arc/INFO
ADS <COVER>

Digitize 4 TICS (using puck):
<number>A 1
<number>A 1
<number>A 1
<number>A 1
0 A

Digitize 2 BNDs

Digitizing cont.

Digitize vertices and nodes:

"0" to locate

"1" to digitize vertex

"2" to digitize node

Exercise 3

Class Notes pages 19-64 will be helpful

Additional Notes on web page, including a rendition of the Digitizing Blues

Use PARCELS map handout

Follow instructions on Exercise 3 VERY CAREFULLY!!!

Mark tic points, label points, nodes

Be Tolerant

WEED Tolerance - sets minimum distance between VERTICES when digitizing

weeds out vertices within this tolerance or distance

SNAP Distance - sets minimum distance between NODES before their locations are snapped together to coincide

Fuzzy tolerance - minimum distance between vertices in terms of resolution of coverage (commonly 0.0002-0.0004) - also defines how far aprat vertices can be moved during the CLEAN process

Try snap distance of 0.1, weed distance of .25

Digitizing for Exercise 3

Mount map on digitizer (may need tape)

Start ADS program in Arc/INFO

ADS ZONES

Digitize 4 TICS

Digitize 2 BNDs

Some Errors

See pages 41-52 in "Class Notes" and additional web notes below

Overshoots - dangling arcs and nodes

Undershoots - node and arc need to be extended

Displayed in ADS or EDITPLOT as square symbols

Pseudonodes - single arc connects with itself or node that splits an arc that should not be split

Displayed in ADS or EDITPLOT as squares

Correcting Errors

Redigitize! Arrghh!

Use ARCEDIT module: tips on backside of PARCELS map handout and also on web page

Notes above from ESRI's ArcDoc Module
Last updated 5 October 1999

http://dusk.geo.orst.edu/arc/265_3.html

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