Welcome, Guest. Please login or register.

Login with username, password and session length
Forums Search:  


Author Topic: Map viewed on PC vs iMac looks different.  (Read 6224 times)

vt.flatlander

  • Mapper
  • ***
  • Posts: 79
  • Karma: 2
    • View Profile
Re: Map viewed on PC vs iMac looks different.
« Reply #15 on: April 15, 2016, 12:03:01 PM »
Boyd
I installed the Pines map to have a look. Looks great. How does a typical modern Garmin GPSr handle that much detail.

 Do you use Orthophotos and satellite imagery laid over your vector map to get the polygon data ?
 It would be fun to create a vector map with the look of a Historic USGS map but I suspect it would take a great deal of time to build one of an entire state even as small as VT.

Boyd

  • Expert Advisor
  • *****
  • Posts: 3815
  • Karma: 43
    • View Profile
Re: Map viewed on PC vs iMac looks different.
« Reply #16 on: April 16, 2016, 03:55:22 AM »
The map works fine, as long as you don't zoom out too far. As you zoom out, the GPS needs to process more data since a larger area is covered. I spent a lot of time on my most recent topo maps trying to optimize the map to improve performance.

The tutorials on this site have always advocated a "dictionary" approcach to setting zoom levels, where each feature type has a default level. But Garmin's format actually allows you to set a specific zoom level for each individual object in the map. So I developed a rather complex system using a relational database where the zoom level of a line segment is determined by how long it is, whether it is in an urban area and other factors. Zoom level for polygons can be set based on their area.

This is a lot of trouble, but it helps. Frankly, it's one reason why I probably won't make any more Garmin maps once I finish a couple projects I've been working on for awhile. The real problem is that Garmin's format is a relic from the 1990's and their GPS hardware is probably 10 years behind the processing power of modern tablets and phones. ;)

The polygon landcover data comes from a very nice dataset available from the state of NJ. They have taken aerial photos and traced the outlines of all the different land use/land cover (LU/LC) areas for the whole state. I have heavily processed this myself, which is an ongoing project I started many years ago.

Working on a larger map of the Mid Atlantic region, I found that Delaware and Maryland also have similar datasets (although they don't track as many separate LULC classifications as NJ). Pennsylvania and New York don't have anything like this. So I guess that small states have invested the resources to develop this kind of database, since planning is more important when you don't have a lot of room. ;)

Look around your states GIS websites, you may find similar data - Google searches for LULC will often find it. For other area, there is a national database called the National Landcover Dataset (NLCD) that was derived from Landsat data. But this is rather low resolution raster data that was processed based on color/reflectivity (or whatever), as opposed to shapefiles that someone actually traced from photos. I have spent a lot of time processing the NLCD data and converting it into landcover polygons for use in NY and PA, and am pretty happy with the results. That has been very complicated, and there is only so far that you can go with a low resolution raster image however.

Have you ever looked at the USGS historic topo collection? Some very cool stuff there, I built two maps from it for southern NJ. One of them is from circa 1900 and the other is circa 1940. One of the challenges is finding the best map of each quad, the quality can very a lot. Then I had to spend a lot of time attempting to match the colors of the different quads, that can also vary considerably.

FWIW, here they are. They are raster imagery in .kmz format for Google Earth. I also have versions that work in smartphone apps. I started building a website to make it easy for people to download my maps in different formats. Eventually I will get it up and running, but have been distracted with other things recently. :)

http://boydsmaps.com/download/becks_pines.zip
http://boydsmaps.com/download/the_pines_in_the_1940s.zip


vt.flatlander

  • Mapper
  • ***
  • Posts: 79
  • Karma: 2
    • View Profile
Re: Map viewed on PC vs iMac looks different.
« Reply #17 on: April 16, 2016, 05:03:08 PM »
Boyd
Thank you for all your input here. I suspect what you are doing is well beyond my capabilities but appreciate your willingness to share.
I will look into what you mention here and see if I can utilize it for my own purposes.
 
On a different note I have a question regarding Typviewer and hex codes.
I notice all the downhill ski trails on my map are the same as major highways but the tutorial assigned code 0x0106 "Overhead Cable"to this. In Typeviewer the hex code associated with "Overhead Cable" is 0x10106 but the cGPSmapper code list has this as 0x0106.
Typeviewer wont let me enter 0106 as the code ?

Boyd

  • Expert Advisor
  • *****
  • Posts: 3815
  • Karma: 43
    • View Profile
Re: Map viewed on PC vs iMac looks different.
« Reply #18 on: April 17, 2016, 04:27:40 AM »
Sorry, I don't know about those line codes. I never use anything greater than 0x29 on my own maps. I believe those codes starting with 0x0100 are for marine charts and they will not be compatible with all gps units. Not really sure though, since I don't use them.

If you want to use 0x0106 in TypViewer, you can enter 001 in the Type box and 06 in the Subtype box. However, when you look at the code that this creates, it seems to come out as 0x01, which is Major Highway, as you said.

TypViewer wants you to enter a leading zero for all the standard types, so for a Major Highway you would normally enter 001 in the Type box and 00 in the subtype box. My take on this is that TypViewer does not think there are any subtypes that can be used with the 001 prefix.

Someone more knowledgeable about this than me will have to give you the real answer though. Again, for my own maps, I just use the safe and standard types no larger than 0x29. You can choose any of them that you aren't already using, define any line style that you like, and then enter "Ski Trail" (or whatever) as the English description.

I also don't understand why anyone would want to use "overhead cable" to specify "ski trail" ;)

vt.flatlander

  • Mapper
  • ***
  • Posts: 79
  • Karma: 2
    • View Profile
Re: Map viewed on PC vs iMac looks different.
« Reply #19 on: April 17, 2016, 06:00:53 AM »
I will go back to QGIS and assign a different code for those lines. I have some other edits to make anyway.
Thank you.