Orthoviewer

Overview

This project will consist of a simple Web browser based map viewer that allows viewing orthophoto sets for the City of Corvallis overlaid with selected raster data.

Objective

To explore what it takes to build a practical browser for multiple city-wide collections of orthophotos. The major issue I expect to address is preparing the orthophoto data by mosaicking and tiling it, and determining best storage format. I am hoping that mapserver already knows a fair bit about managing the tiled image files. Emphasis will be on preserving image details (ie avoiding use of lossy compression) while serving data over a typical 256K broadband connection.

Implementation

Vector layers available: Streets overlay; centerline or curbs depending on currently selected scale. Taxlots available but not normally displayed. (Used for queries.) Possibly a few other vector layers such as railroads, city limits. These layers are intended to provide orientation and can be switched off to allow concentrating on the content of the aerial photos.

Raster layers available: orthophoto sets for various years from 1936 to present. Sets are selected by year, and only one set can be selected at a time.

User interface

Two maps are visible, a large map and a small reference map. The reference map shows full extent with indicator of extent of large map.

Mode: zoom in, zoom out, pan
Effect of clicking on large map depends on the currently selected mode. Zoom in: click= zoom in a fixed amount and recenter. click-and-drag= creates an extent box and zooms to the new extent. Zoom out: click or click-and-drag= zooms out and recenters. Pan: click= recenter; click-and-drag= pan

Actions buttons:
Full extent: zooms to full extent of map
Redraw: sends command to mapserver to redraw the large map

Selection list: Make a selection from a "places" list and then zoom to the place. (Should the list change based on the selected photo set??)

Wish list: (features for version 2.0)

• Search: Query the taxlots database then allow zooming to the vicinity of that taxlot. Save this feature for release 2.0 :-)
• Print: opens a popup with a map formatted for printing on 8.5x11 paper
• Download the displayed map as a jpeg or pdf file
• Two large map frames, so that two maps with same extent but orthos for different years can be compared side-by-side.

Additional Comments

Appearance: The Web pages should look good. The maps should conform to basic cartographic principles.

Robustness: the user interface should screen out bad data entry such as zooming in and out beyond reasonable limits or panning outside the full extent.

This project will be mostly server-side oriented using php/Mapscript.

Implementation of some user-interface features will be either javascript or flash/swf; to be determined.

It will not be browser dependent; testing will be done on current versions of Mozilla and Firefox on Linux and Windows, and Internet Explorer on Windows.

Data storage: vector files will be ESRI shapefile format. Raster files will (probably) be tiled geotiffs prepared using fwtools.