Orienteering NZ Wiki

And other sources of “global” imagery such as Bing, Apple. Their benefits and limitations and how to get them into our mapping software.

The topic “Mapping” under “Events and Training” is getting unweildy whereas this one under “Technical” is underused. I carry on the discussion of Google Earth as a source of aerial photos. GE is a free internet application which provides amazingly good aerial photos of the entire earth. The resolution and age of the photos vary, but eg I can see that there's a white car outside my house. There are however “holes” in the coverage with only reduced resolution, or cloud in the way. You need broadband.

Thanks to Martin I have improved my understanding of how to use these as templates in OCAD. First of all download the latest version 4 which is significantly better than v3. Secondly switch off the “terrain” layer which seems to distort things somehow. Thirdly switch off the sidebar and you'll see more at a time.

There are two ways to grab the image which I think is always 1024 X 693 pixels with the sidebar off: File –> Save Image which makes a jpg of about 130k, and Edit –> Copy which puts the image onto the clipboard where you can paste it into anything else.

A reason for taking it somewhere other than OCAD is that the higher resolution the smaller the area within the fixed window. So if you want to see every gorse bush you'll have heaps of images and you might want to join them together before opening them as a template in OCAD. For 1:15,000 maps where its a generalised edge of the gorse that's of interest then not zooming in so far will result in more in the picture and fitting the separate images in OCAD may be fine.

In my original posting on this I couldn't understand why I couldn't see as much in OCAD. The answer is that the resolution was “frozen” at the time of capture from GE, and no amount of zooming in OCAD can get any more detail. So you make your decision in GE at the time you save the image.

Finally you'll need a basemap of some sort to fit the images to. Most existing maps have an arbitrary coordinate origin and are unrelated to “the real world”. Starting at an arbitrary point and tacking bits on the side is bound to create distortion which will eventually cause problems. You could use a low-resolution GE image from which you trace say the road network (after rotating to magnetic north of course). I favour the LINZ orthophotos, free on the LINZ website. They have less resolution than GE but are fine for setting up a framework in terms of the NZ Map Grid which then allows other sources of info (eg coords from a GPS) to be used in OCAD. But that's another story. Would love to hear from others who have used GE.

I have only recently started using Google Earth images for mapping and I was surprised how good the photos are compared to the ones I have been getting from the city council. The images I have looked at so far are less than 2 years old and it is amazing the informatio you can get from from a photo afer enhancing it at the editing stage. However, GE has some limitationg, the map I am working on at the moment is obscured by a large cloud and I need the aerial photo to map the many patches of gorse.

I can certainly see GE as being of great value to mappers in the future. Some day they may even provide us with free photogrammetry.

Thanks Greg you are right. Therefore I would encourage mappers to use the “Mapping” topic with the (at present) smaller number of replies. What sort of enhancing do you do Svend?

Re: enhancement of GE images I edit the image in “Arc Soft Photo Studio” before saving it to OCAD. I always enhance the image with “Brightness” and “Contrast” so I can actually see the details. Other enhancement depend on what I want to map. If I want to map the clearings in a forest I use the “Special Filter” called “Find Contour” (nothing to do with contours), I select the green colour and have the blue and red turned off. With a click of the mouse and a little adjustment all vegetation boundaries will be shown with a green line.Nothing else is shown. Since the template is totally dark apart from the green lines it is necessary to draw the vegetation boundaries off the map or use registration marks to adjust the template. There are about eighteen different functions in the “Enhance Menu” and some of them I haven't tried out yet. The “Sharpen Filter”, “Sharpen Vertically” has proven very usefull in identifying large trees in native bush.

On my Windows 7 machine I can't get Google Earth to reduce its window width below some minimum, a test suggests 780 pixels. Height yes, but even dragging a corner only affects it vertically. I've been used to having GE and OCAD side by side, and this doesn't leave enough for OCAD. A google search doesn't suggest anything. Any ideas?

Don't drag the corner drag the whole Google Earth window to the left or the right so only part of it is on the screen.

Buy a bigger screen? ;-D

I have two screens at work which is great for comparison.

For all my Ocad work, I use my laptop (in the lounge), rather than my desktop in my office at home.

I like this monitor - don't need two. Cheap at the moment too. http://www.pbtech.co.nz/index.php?z=p&p=MONDEL2913&name=Dell-UltraSharp-U2913WM-29-Ultra-wide-IPS-Monitor-

I always thought I had a method that would give me the latest GE photos. View menu, tick historical imagery, and move the slider as far right as it will go. Found a case where there's later imagery THAN THAT, I can view it when historical imagery is switched off. Is there an explanation, or is that just a glitch?