Grid displays incorrectly when using custom grid with +towgs84

[dennis15926]

Hello from Taiwan!

I've noticed that the on-screen grid (Show/hide Grid) does not display properly when using a Custom Grid that has Proj4 conversions using +towgs84
My guess is that the grid is created before the Geodetic Conversion happens.

Case in point:
In Taiwan we use the TWD67 Coordinates, but the ESPG listing is incorrect; it is off by ~800 meters. The correct conversion is:

Code Select Expand

+proj=tmerc +lat_0=0 +lon_0=121 +k=0.9999 +x_0=250000 +y_0=0 +ellps=aust_SA +towgs84=-752,-358,-179,-0.0000011698,0.0000018398,0.0000009822,0.00002329 +units=m +no_defs
reference: Academia Sinica Blog

With this conversion, the coordinates shown in the coordinate box are accurate. But, the grid is drawn at the wrong place (misalignment of y:170, x:-805). This can be seen in the screenshot. Supposedly, the grid should be drawn at the coordinates (XXX000, XXXX000), but instead are at (XXX170, XXXX195)

Hopefully, this can be corrected, as it will be of great help to the Taiwan hiking community. If needed, I can help debug the source code.

BTW, Oruxmaps is really popular with the hiking community in Taiwan. Thanks for making such a great app!

[orux]

Thanks;
You are right;
I think I can have a solution in next version:



orux

[dennis15926]

Hi Orux,

Thanks so much for the prompt response and quick fix 

Just wanted to share a few links from the Taiwan hiking / mapping community. It's in Traditional Chinese, but you can see Oruxmaps screenshots everywhere in the posts

http://rudy.basecamp.tw/taiwan_topo.html
https://www.facebook.com/groups/taiwan.topo
https://www.facebook.com/groups/664516810370602/post_tags/?post_tag_id=1500861583402783

Thank you again for making all this possible for us hikers in Taiwan!!

[orux]

Hi Orux,

Thanks so much for the prompt response and quick fix 

Just wanted to share a few links from the Taiwan hiking / mapping community. It's in Traditional Chinese, but you can see Oruxmaps screenshots everywhere in the posts

http://rudy.basecamp.tw/taiwan_topo.html
https://www.facebook.com/groups/taiwan.topo
https://www.facebook.com/groups/664516810370602/post_tags/?post_tag_id=1500861583402783

Thank you again for making all this possible for us hikers in Taiwan!!

Thanks!

I am happy to see how the app is used around the world.

That's the best thing about developing the app!

orux