Want to auto-digitize contour lines, otherwise it would be impossible to do it "heads-up" style (manually)

Take a binary image, and create digitized curves

-simple alogorthm to make lines one pixel thick.

Then transform to vector data

The science of obtaining reliable measurements from photography.

The results can be:

-coordinates of the required object-points

-topographical and thematical maps

-and rectified photographs (orthophotos get produced by people who do photogrammetry)

National mapping strategy working group, Canadian council on geomatics (2010)

1. Growing realization that geography/geographic information is required in a modern world - needs of citizens.

2. Long-term approach to planning and coordination

3. National Standard for Spatial Data Accuracy established by the Federal Geographic Data Committee in 1998.

Elements of the Strategy are:

Consultative and Inclusive Governance

-working cooperatively will provide clarity, direction, and certainty for Canada's mapping comunity by providing a forum to share information, methodologies, approaches to mapping and timelines.

-"prevent us from going Egyptian"

National Approach, Regional and Local Decision Making

-effective and responsive policies that respect the autonomy of mapping agencies and organizations while promoting cooperation and coordination are crucial to the implementation of the National Mapping Strategy

Common Technological Foundation

-A major challenge for the NMS will be to ensure that the broad technical and data standards required for interoperability continue to be promoted and their adoption encouraged.

Current and Available Data

-New approaches to data maintenance and updating cycles will be designed and implemented to ensure that data sets required by decision makers are as current and accurate as required.

Geographical Data as a Public Asset

-The NMS recognizes the importance and value of 'no charge', unrestricted access to overnment mapping data when there is no threat created by the release of the data.

Outreach and Communications

-A concerted effort will be made to inform non-traditional users of Geomatics technologies, and to inform policy and decision makers of the enriched information and analytical power that can be obtained through the use of geomatics and how this can substantially benefit the work they do.

A VibrantGeomatics Industry

-A central component of the NMS is a competitive, productive geomatics .......

Available Educated Labour Force

-Promoting opportunities for education in geomatics, ranging from technologists, to engineers to analysts, in order that there are qualified Canadian workers to meet the challenges of the future is important for the sustainability of the community.

Began in 2007- a little late by global standards.

GIS is the driving force.

Internet and development of geographic data sharing.

Relationshps b/w different levels of government.

Growth of mass market applications presented policy and operational challenges for mapping organizations.

3289 companies reported as being involved in surveying and mapping in 2007 Stats Can survey.

2.8 billion annual revenue

23000 Canadians employed mapping sector.

Information and technology sector.

Location errors refer to the geometric inaccuracies of digitized features.

Location errors can be examined by referring to the data source for digitizing.

-easy to do when looking in a heads-up environment

Trying to minimize source error as well. Error terms are additive. If you have multiple sources that created the data, you add up all their errors.

Sources of error include extreme boredom or fatigue.

Top errors violate the topological relationships either required by a GIS paxkage or defined by the user.

TYPES

Topological errors with geometric features:

-undershoot

-overshoot

-dangling node

-pseudo node

-directional error

-label error

Topological errors b/w layers: boundaries not coincident, lines not connected at end points, overlapping line features, etc.

-ie. contour lines done with two projections

Solution: use your existing data to update! Don't start fresh!

Topological editing ensures that digitized spatial fewatures follow the topological relationships that are either built into a data model or specified by the user

1. Topological Editing on coverages

2.Editing using map topology

3.Editing using topology

You can't do any topological work if you have a topological error.

The fuzzy tolerance can snap an fix most of these problems...

....see these slides.... skipped quite a few (mostly figures from the book.... chap 7?... March 2... lec 19?).

Edgematching matches lines along the edge of a layer to lines of an adjacent layer so that the lines are continuous across the border.... (missed some)

Edgematching matches the lines of two adjacent layers so that the lines are continuous along the border.

-removing the edge and creating a single polygon.

-it is professional torture. The least amount of fun you can possibly have.

Simplification refers to the process of simplifying or generalizing a line by removing some of its points.

Smoothing refers to .... (missed)

Douglas and Poiker (Peuker)

-1973, SFU

Given a curve composed of line segments, find a curve with fewer points.

-reduce redundancy; point-happiness

-happens during streaming (create points automatically as you move cursor)

Dissimilar based on maximum distance between the original curve and the simplified curve.

It is a recursive algorithm. Have to do it more than once. Until line can be no simpler based on the tolerance you have set.

D-P Algorithm

-marks the first and last point- keeps them.

-its got a line, and says give me the nodes.

Find the point that is furthest from the line segment with the first and last points defining a line.

-if it reaches the tolerance, keep it.

Compares the points to the distance dimension (tolerance of line variation)

If the line meets the distance dimension criterion, it is kept, if not then points that exceed the distance dimension are kept.

Iterates until all points in the new line meet the distance criterion.

** check out slide 33, Mar2

Dissects line into a series of bends

Calculates the geometric properties of each bend.

Removes bends that are considered insignificant.

Makes use of tolerance.

Concerned with the overall shape of the line.

Smoother line... slower